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Freescale Semiconductor Advance Information
Document number: MC34712 Rev. 4.0, 5/2007
3.0 A 1.0 MHz Fully Integrated DDR Switch-Mode Power Supply
The 34712 is a highly integrated, space efficient, low cost, single synchronous buck switching regulator with integrated N-channel power MOSFETs. It is a high performance point-of-load (PoL) power supply with the ability to track an external reference voltage. Its high efficient 3.0 A sink and source capability combined with its voltage tracking/sequencing ability and tight output regulation, makes it ideal to provide the termination voltage (VTT) for modern data buses such as Double-Data-Rate (DDR) memory buses. It also provides a buffered output reference voltage (VREF) to the memory chipset The 34712 offers the designer the flexibility of many control, supervisory, and protection functions to allow for easy implementation of complex designs. It is housed in a Pb-Free, thermally enhanced, and space efficient 24-Pin Exposed Pad QFN. Features * 45 m Integrated N-Channel Power MOSFETs * Input Voltage Operating Range from 3.0 V to 6.0 V * 1 % Accurate Output Voltage, Ranging from 0.7 V to 1.35 V * 1 % Accurate Buffered Reference Output Voltage * Programmable Switching Frequency Range from 200 kHz to 1.0 MHz with a default of 1.0 MHz * Over Current Limit and Short Circuit Protection * Thermal Shutdown * Output Overvoltage and Undervoltage Detection * Active Low Power Good Output Signal * Active Low Standby and Shutdown Inputs * Pb-Free Packaging Designated by Suffix Code EP.
VIN (3.0V TO 6.0V)
34712
SWITCH-MODE POWER SUPPLY
EP SUFFIX 98ARL10577D 24-PIN QFN
ORDERING INFORMATION
Device MC34712EP/R2 Temperature Range (TA) -40 to 85C Package 24 QFN
34712
PVIN VDDQ VREFIN SW VIN VDDI FREQ GND SD VOUT VDDQ MEMORY BUS BOOT VTT TERMINATING RESISTORS
INV
COMP VREFOUT PGND PG VIN
DDR MEMORY CHIPSET VREF DDR MEMORY CONTROLER VDDQ
MCU
STBY
Figure 1. 34712 Simplified Application Diagram
* This document contains certain information on a new product. Specifications and information herein are subject to change without notice.
(c) Freescale Semiconductor, Inc., 2007. All rights reserved.
INTERNAL BLOCK DIAGRAM
INTERNAL BLOCK DIAGRAM
STBY Thermal Monitoring PG M1 Ise nse System Reset Current Monitoring Discharge I li mit
SD Internal Voltage Regulator
VIN
System Control
VDDI
M2
BOOT
VIN
VBOOT
PVIN M3 SW
Oscillator FREQ Prog. Frequency
Buck Cntl. Logic
FSW
Gate Driver Isense
M4 V DDI VDDI Bandgap Regulator VREFIN RREF1 RREF2 Buffer M6 Discharge M5 Discharge VOUT V BG PWM Comparator Error Amplifier INV PGND COMP
Ramp Generator
GND
VREFOUT
Figure 2. 34712 Simplified Internal Block Diagram
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Analog Integrated Circuit Device Data Freescale Semiconductor
PIN CONNECTIONS
PIN CONNECTIONS
BOOT
VDDI
PVIN
24
GND FREQ NC PG STBY SD
23
22
21
20
19 18 PVIN 17
SW SW SW
1 2 3 4 5 6 7
VREFIN Transparent Top View
PVIN
VIN
VIN
16 15
14 PGND 13 8
VREFOUT PGND
9
COMP
10
INV
11
VOUT
12
PGND
Figure 3. 34712 Pin Connections Table 1. 34712 Pin Definitions A functional description of each pin can be found in the Functional Pin Description section beginning on page 10.
Pin Number 1 2 3 4 5 6 7 8 9 10 11 12,13,14 15,16,17 18,19,20 21 Pin Name GND FREQ NC PG
STBY SD
Pin Function Ground Passive None Output Input Input Input Output Passive Input Output Ground Power Supply Passive
Formal Name Signal Ground Analog signal ground of IC
Definition
Frequency Adjustment Buck converter switching frequency adjustment pin No Connect Power Good Standby Shutdown Voltage-TrackingReference Input Reference Voltage Output Compensation Error Amplifier Inverting Input Output Voltage Discharge FET Power Ground Switching Node Power-Circuit Supply Input Bootstrap No internal connections to this pin Active-low (open drain) power-good status reporting pin Standby mode input control pin Shutdown mode input control pin Voltage-Tracking-Reference voltage input Buffered output equal to 1/2 of voltage-tracking reference Buck converter external compensation network pin Buck converter error amplifier inverting input pin Discharge FET drain connection (connect to buck converter output capacitors) Ground return for buck converter and discharge FET Buck converter power switching node Buck converter main supply voltage input Bootstrap switching node (connect to bootstrap capacitor)
VREFIN VREFOUT
COMP
INV VOUT PGND SW PVIN BOOT
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PIN CONNECTIONS
Table 1. 34712 Pin Definitions (continued) A functional description of each pin can be found in the Functional Pin Description section beginning on page 10.
Pin Number 22,23 24 Pin Name
VIN
Pin Function Supply Passive
Formal Name Logic-Circuit Supply Input Internal Voltage Regulator
Definition Logic circuits supply voltage input Internal Vdd Regulator (connect filter capacitor to this pin)
VDDI
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ELECTRICAL CHARACTERISTICS MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
MAXIMUM RATINGS
Table 2. Maximum Ratings All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent damage to the device.
Ratings ELECTRICAL RATINGS Input Supply Voltage (VIN) Pin High-Side MOSFET Drain Voltage (PVIN) Pin Switching Node (SW) Pin BOOT Pin (Referenced to SW Pin) PG, VOUT, SD, and STBY Pins VDDI, FREQ, INV, COMP, VREFIN, and VREFOUT Pins Continuous Output Current (1) ESD Voltage (2) Human Body Model Device Charge Model (CDM) THERMAL RATINGS Operating Ambient Temperature (3) Storage Temperature Peak Package Reflow Temperature During Reflow Maximum Junction Temperature Power Dissipation (TA = 85 C)
(6) (4), (5)
Symbol
Value
Unit
VIN PVIN VSW VBOOT - VSW IOUT VESD1 VESD3
-0.3 to 7.0 -0.3 to 7.0 -0.3 to 7.5 -0.3 to 7.5 -0.3 to 7.0 -0.3 to 3.0 3.0
V V V V V V A
2000 750
V
TA TSTG TPPRT TJ(MAX) PD
-40 to 85 -65 to +150 Note 5 +150 2.9
C C C C W
Notes 1. Continuous output current capability so long as TJ is TJ(MAX). 2. 3. 4. 5. ESD1 testing is performed in accordance with the Human Body Model (CZAP = 100 pF, RZAP = 1500 ), ESD3 testing is performed in accordance with the Charge Device Model (CDM). The limiting factor is junction temperature, taking into account power dissipation, thermal resistance, and heatsinking. Pin soldering temperature limit is for 10 seconds maximum duration. Not designed for immersion soldering. Exceeding these limits may cause malfunction or permanent damage to the device. Freescale's Package Reflow capability meets Pb-free requirements for JEDEC standard J-STD-020C. For Peak Package Reflow Temperature and Moisture Sensitivity Levels (MSL), Go to www.freescale.com, search by part number [e.g. remove prefixes/suffixes and enter the core ID to view all orderable parts. (i.e. MC33xxxD enter 33xxx), and review parametrics. Maximum power dissipation at indicated ambient temperature.
6.
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ELECTRICAL CHARACTERISTICS MAXIMUM RATINGS
Table 2. Maximum Ratings (continued) All voltages are with respect to ground unless otherwise noted. Exceeding these ratings may cause a malfunction or permanent damage to the device.
Ratings THERMAL RESISTANCE (7) Thermal Resistance, Junction to Ambient, Single-Layer Board (1s) (8) Thermal Resistance, Junction to Ambient, Four-Layer Board (2s2p) Thermal Resistance, Junction to Board
(10) (9)
Symbol
Value
Unit
RJA RJMA RJB
139 43 22
C/W C/W C/W
Notes 7. The PVIN, SW, and GND pins comprise the main heat conduction paths. 8. Per SEMI G38-87 and JEDEC JESD51-2 with the single-layer board (JESD51-3) horizontal. 9. Per JEDEC JESD51-6 with the board (JESD51-7) horizontal. There are no thermal vias connecting the package to the two planes in the board. 10. Thermal resistance between the device and the printed circuit board per JEDEC JESD51-8. Board temperature is measured on the top surface of the board near the package.
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ELECTRICAL CHARACTERISTICS STATIC ELECTRICAL CHARACTERISTICS
STATIC ELECTRICAL CHARACTERISTICS
Table 3. Static Electrical Characteristics Characteristics noted under conditions 3.0 V VIN 6.0 V, - 40C TA 85C, GND = 0 V unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions unless otherwise noted.
Characteristic IC INPUT SUPPLY VOLTAGE (VIN) Input Supply Voltage Operating Range Input DC Supply Current (11) Normal Mode: SD = 1 & STBY = 1, Unloaded Outputs Input DC Supply Current (11) Standby Mode, SD = 1 & STBY = 0 Input DC Supply Current (11) Shutdown Mode, SD = 0 & STBY = X INTERNAL SUPPLY VOLTAGE OUTPUT (VDDI) Internal Supply Voltage Range BUCK CONVERTER (PVIN, SW, GND, BOOT, INV, COMP) High-side MOSFET Drain Voltage Range Output Voltage Adjustment Range Output Voltage Accuracy Line Regulation
(12) (12)
Symbol
Min
Typ
Max
Unit
VIN IIN IINQ IINOFF
3.0 -
-
6.0 25
V
mA
-
-
15
mA
-
-
100
A
VDDI
2.35
2.5
2.65
V
PVIN VOUT REGLN REGLD
2.5 0.7 -1.0 -1.0
-
6.0 1.35 1.0 1.0
V V % %
(12), (13), (14)
Normal Operation, VIN = 3.0 V to 6.0 V, IOUT = 3.0 A Load Regulation (12) Normal Operation, IOUT = -3.0 A to 3.0 A Error Amplifier Common Mode Voltage Range (12), (15) Output Undervoltage Threshold Output Overvoltage Threshold Continuous Output Current Over Current Limit, Sinking and Sourcing Short Circuit Current Limit (Sourcing and Sinking) High-Side N-CH Power MOSFET (M3) RDS(ON) (12) IOUT = 1.0 A, VBOOT - VSW = 3.3 V Low-Side N-CH Power MOSFET (M4) RDS(ON) (12) IOUT = 1.0 A, VIN = 3.3 V Notes 11. 12. 13. 14. 15.
-1.0 0.0 -1.5 1.5 -3.0 -
4.0 6.5
1.0 1.35 -8.0 8.0 3.0 -
% V % % A A A
VREF
VUVR VOVR IOUT ILIM ISHORT RDS(ON)HS RDS(ON)LS
10
-
45
m
10
-
45
m
See section "MODES OF OPERATION", page 14 has a detailed description of the different operating modes of the 34712 Design information only, this parameter is not production tested. 1% is assured at room temperature. Overall output accuracy is directly affected by the accuracy of the external feedback network, 1% feedback resistors are recommended. The 1% output voltage regulation is only guaranteed for a common mode voltage range greater than or equal to 0.7V at room temperature.
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ELECTRICAL CHARACTERISTICS STATIC ELECTRICAL CHARACTERISTICS
Table 3. Static Electrical Characteristics Characteristics noted under conditions 3.0 V VIN 6.0 V, - 40C TA 85C, GND = 0 V unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions unless otherwise noted.
Characteristic M2 RDS(ON) (VIN = 3.3 V, M2 is on) PVIN Pin Leakage Current (Standby and Shutdown Modes) INV Pin Leakage Current Thermal Shutdown Threshold Thermal Shutdown Hysteresis OSCILLATOR (FREQ) Oscillator Frequency Adjusting Reference Voltage Range TRACKING (VREFIN, VREFOUT, VOUT) VREFIN External Reference Voltage Range (16) VREFOUT Buffered Reference Voltage Range VREFOUT Buffered Reference Voltage Accuracy
(17) (16) (16)
Symbol RDS(ON)M2 IPVIN IINV TSDFET TSDHYFET
Min 1.5
Typ -
Max 4.0
Unit
-10 -1.0 -
170 25
10 1.0 -
A A C C
VFREQ
0.0
-
VDDI
V
VREFIN VREFOUT IREFOUT IREFOUTLIM RTDR(M6) RTDR(M5) IVOUTLKG
0.0 0.0 -1.0 0.0 -1.0
11 50 50 -
2.7 1.35 1.0 8.0 1.0
V V % mA mA A
VREFOUT Buffered Reference Voltage Current Capability VREFOUT Buffered Reference Voltage Over Current Limit VREFOUT Total Discharge Resistance VOUT Total Discharge Resistance (16)
(16)
VOUT Pin Leakage Current (Standby Mode, VOUT = 3.6 V) CONTROL AND SUPERVISORY (STBY, SD, PG) STBY High Level Input Voltage STBY Low Level Input Voltage STBY Pin Internal Pull Up Resistor SD High Level Input Voltage SD Low Level Input Voltage SD Pin Internal Pull Up Resistor PG Low Level Output Voltage (IPG = 3.0 mA) PG Pin Leakage Current (M1 is off, Pulled up to VIN) IPGLKG -1.0 1.0 A VPGLO 0.4 V VSTBYHI VSTBYLO RSTBYUP VSDHI VSDLO RSDUP 2.0 1.0 2.0 1.0 0.4 2.0 0.4 2.0 V V M V V M
Notes 16. Design information only, this parameter is not production tested. 17. The 1 % accuracy is only guaranteed for VREFOUT greater than or equal to 0.7 V at room temperature.
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ELECTRICAL CHARACTERISTICS DYNAMIC ELECTRICAL CHARACTERISTICS
DYNAMIC ELECTRICAL CHARACTERISTICS
Table 4. Dynamic Electrical Characteristics Characteristics noted under conditions 3.0 V VIN 6.0 V, - 40C TA 85C, GND = 0 V unless otherwise noted. Typical values noted reflect the approximate parameter means at TA = 25C under nominal conditions unless otherwise noted.
Characteristic BUCK CONVERTER (PVIN, SW, GND, BOOT) Switching Node (SW) Rise Time (19) (PVIN = 3.3 V, IOUT = 3.0 A) Switching Node (SW) Fall Time (19) (PVIN = 3.3 V, IOUT = 3.0 A) Soft Start Duration (Normal Mode) Over Current Limit Timer Over Current Limit Retry Time-out Period Output Undervoltage/Overvoltage Filter Delay Timer OSCILLATOR (FREQ) Oscillator Default Switching Frequency (18) (FREQ = GND) Oscillator Switching Frequency Range CONTROL AND SUPERVISORY (STBY, SD, PG) PG Reset Delay Thermal Shutdown Retry Time-out Period (19) Notes 18. Oscillator Frequency tolerance is 10%. 19. Design information only, this parameter is not production tested. tPGRESET tTIMEOUT 8.0 80 12 120 ms ms FSW FSW 200 1.0 1000 MHz kHz tSS tLIM tTIMEOUT tFILTER 1.3 80 5.0 10 2.6 120 25 ms ms ms s tFALL 20 ns tRISE 14 ns Symbol Min Typ Max Unit
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FUNCTIONAL DESCRIPTION INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
In modern microprocessor/memory applications, address commands and control lines require system level termination to a voltage (VTT) equal to 1/2 the memory supply voltage (VDDQ). Having the termination voltage at midpoint, the power supply insures symmetry for switching times. Also, a reference voltage (VREF) that is free of any noise or voltage variations is needed for the DDR SDRAM input receiver, VREF is also equal to 1/2 VDDQ. Varying the VREF voltage will effect the setup and hold time of the memory. To comply with DDR requirements and to obtain best performance, VTT and VREF need to be tightly regulated to track 1/2 VDDQ across voltage, temperature, and noise margins. VTT should track any variations in the DC VREF value (VTT = VREF +/- 40 mV), (See Figure 4) for a DDR system level diagram. The 34712 supplies the VTT and a buffered VREF output. To ensure compliance with DDR specifications, the VDDQ line is applied to the VREFIN pin and divided by 2 internally through a precision resistor divider. This internal voltage is then used as the reference voltage for the VTT output. The same internal voltage is also buffered to give the VREF voltage at the VREFOUT pin for the application to use without the need for an external resistor divider. The 34712 provides the tight voltage regulation and power sequencing/tracking required along with handling the DDR peak transient current requirements. Buffering the VREF output helps its immunity against noise and load changes. The 34712 utilizes a voltage mode synchronous buck switching converter topology with integrated low RDS(ON) (45 m) N-channel power MOSFETs to provide a VTT voltage with an accuracy of less than 2.0 %. It has a programmable switching frequency that allows for flexibility and optimization over the operating conditions and can operate at up to 1.0 MHz to significantly reduce the external components size and cost. The 34712 can sink and source up to 3.0 A of continuous current. It provides protection against output over current, overvoltage, undervoltage, and overtemperature conditions. It also protects the system from short circuit events. It incorporates a power-good output signal to alert the host when a fault occurs. For boards that support the Suspend-To-RAM (S3) and the Suspend-To-Disk (S5) states, the 34712 offers the STBY and the SD pins respectively. Pulling any of these pins low, puts the IC in the corresponding state. By integrating the control/supervisory circuitry along with the Power MOSFET switches for the buck converter into a space-efficient package, the 34712 offers a complete, smallsize, cost-effective, and simple solution to satisfy the needs of DDR memory applications. Besides DDR memory termination, the 34712 can be used to supply termination for other active buses and graphics card memory. It can be used in Netcom/Telecom applications like servers. It can also be used in desktop motherboards, game consoles, set top boxes, and high end high definition TVs.
VDDQ
VTT
VDDQ
RS
BUS
RT VREF
DDR Memory Controller
DDR Memory Input Receiver
Figure 4. DDR System Level Diagram
FUNCTIONAL PIN DESCRIPTION REFERENCE VOLTAGE INPUT (VREFIN)
The 34712 will track 1/2 the voltage applied at this pin.
FREQUENCY ADJUSTMENT INPUT (FREQ)
The buck converter switching frequency can be adjusted by connecting this pin to an external resistor divider between VDDI and GND pins. The default switching frequency (FREQ pin connected to ground, GND) is set at 1.0 MHz.
REFERENCE VOLTAGE OUTPUT (VREFOUT)
This is a buffered reference voltage output that is equal to 1/2 VREFIN. It has a 10.0 mA current drive capability. This output is used as the VREF voltage rail and should be filtered against any noise. Connect a 0.1 F, 6 V low ESR ceramic filter capacitor between this pin and the GND pin and between this pin and VDDQ rail. VREFOUT is also used as the reference voltage for the buck converter error amplifier.
SIGNAL GROUND (GND)
Analog ground of the IC. Internal analog signals are referenced to this pin voltage.
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FUNCTIONAL DESCRIPTION FUNCTIONAL PIN DESCRIPTION
INTERNAL SUPPLY VOLTAGE OUTPUT (VDDI)
This is the output of the internal bias voltage regulator. Connect a 1.0 F, 6 V low ESR ceramic filter capacitor between this pin and the GND pin. Filtering any spikes on this output is essential to the internal circuitry stable operation.
POWER INPUT VOLTAGE (PVIN)
Buck converter power input voltage. This is the drain of the buck converter high-side power MOSFET.
BOOTSTRAP INPUT (BOOT)
Bootstrap capacitor input pin. Connect a capacitor (as discussed on page 19) between this pin and the SW pin to enhance the gate of the high-side Power MOSFET during switching.
OUTPUT VOLTAGE DISCHARGE PATH (VOUT)
Output voltage of the Buck Converter is connected to this pin. it only serves as the output discharge path once the SD signal is asserted.
SHUTDOWN INPUT (SD) ERROR AMPLIFIER INVERTING INPUT (INV)
Buck converter error amplifier inverting input. Connect the VTT voltage directly to this pin. If this pin is tied to the GND pin, the device will be in Shutdown Mode. If left unconnected or tied to the VIN pin, the device will be in Normal Mode. The pin has an internal pull up of 1.5 M. This input accepts the S5 (Suspend-To-Disk) control signal.
COMPENSATION INPUT (COMP)
Buck converter external compensation network connects to this pin. Use a type III compensation network.
STANDBY INPUT (STBY)
If this pin is tied to the GND pin, the device will be in Standby Mode. If left unconnected or tied to the VIN pin, the device will be in Normal Mode. The pin has an internal pull up of 1.5 M. This input accepts the S3 (Suspend-To-RAM) control signal.
INPUT SUPPLY VOLTAGE (VIN)
IC power supply input voltage. Input filtering is required for the device to operate properly.
POWER GROUND (PGND)
Buck converter and discharge MOSFETs power ground. It is the source of the buck converter low-side power MOSFET.
POWER GOOD OUTPUT SIGNAL (PG)
This is an active low open drain output that is used to report the status of the device to a host. This output activates after a successful power up sequence and stays active as long as the device is in normal operation and is not experiencing any faults. This output activates after a 10 ms delay and must be pulled up by an external resistor to a supply voltage (e.g.,VIN.).
SWITCHING NODE (SW)
Buck converter switching node. This pin is connected to the output inductor.
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FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
Internal Bias Circuits
System Control & Logic
Oscillator
Protection Functions
Control & Supervisory Functions
Tracking & Sequencing
Buck Converter
Figure 5. 34712 Internal Block Diagram
INTERNAL BIAS CIRCUITS
This block contains all circuits that provide the necessary supply voltages and bias currents for the internal circuitry. It consists of: * Internal Voltage Supply Regulator: This regulator supplies the VDDI voltage that is used to drive the digital/ analog internal circuits. It is equipped with a Power-OnReset (POR) circuit that watches for the right regulation levels. External filtering is needed on the VDDI pin. This block will turn off during the shutdown mode. * Internal Bandgap Reference Voltage: This supplies the reference voltage to some of the internal circuitry. * Bias Circuit: This block generates the bias currents necessary to run all of the blocks in the IC.
resistor divider to the FREQ pin, between VDDI and GND pins (See Figure 1).
PROTECTION FUNCTIONS
This block contains the following circuits: * Over Current Limit and Short Circuit Detection: This block monitors the output of the buck converter for over current conditions and short circuit events and alerts the system control for further command. * Thermal Limit Detection: This block monitors the temperature of the device for overheating events. If the temperature rises above the thermal shutdown threshold, this block will alert the system control for further commands. * Output Overvoltage and Undervoltage Monitoring: This block monitors the buck converter output voltage to ensure it is within regulation boundaries. If not, this block alerts the system control for further commands.
SYSTEM CONTROL AND LOGIC
This block is the brain of the IC where the device processes data and reacts to it. Based on the status of the STBY and SD pins, the system control reacts accordingly and orders the device into the right status. It also takes inputs from all of the monitoring/protection circuits and initiates power up or power down commands. It communicates with the buck converter to manage the switching operation and protects it against any faults.
CONTROL AND SUPERVISORY FUNCTIONS
This block is used to interface with an outside host. It contains the following circuits: * Standby Control Input: An outside host can put the 34712 device into standby mode (S3 or Suspend-ToRAM mode) by sending a logic "0" to the STBY pin. * Shutdown Control Input: An outside host can put the 34712 device into shutdown mode (S5 or Suspend-ToDisk mode) by sending a logic "0" to the SD pin. * Power Good Output Signal PG: The 34712 can communicate to an external host that a fault has
OSCILLATOR
This block generates the clock cycles necessary to run the IC digital blocks. It also generates the buck converter switching frequency. The switching frequency has a default value of 1.0 MHz and can be programmed by connecting a
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FUNCTIONAL DESCRIPTION FUNCTIONAL INTERNAL BLOCK DESCRIPTION
occurred by releasing the drive on the PG pin high, allowing the signal/pin to be pulled high by the external pull-up resistor.
TRACKING AND SEQUENCING
This block allows the output of the 34712 to track 1/2 the voltage applied at the VREFIN pin. This allows the VREF and VTT voltages to track 1/2 VDDQ and assures that none of them will be higher than VDDQ at any point during normal operating conditions. For power down during a shutdown (S5) mode, the 34712 uses internal discharge MOSFETs (M5 and M6 on Figure 2) to discharge VTT and VREF respectively. These discharge MOSFETs are only active during shutdown mode. Using this block along with controlling the SD and STBY pins can offer the user power sequencing capabilities by controlling when to turn the 34712 outputs on or off.
BUCK CONVERTER
This block provides the main function of the 34712: DC to DC conversion from an un-regulated input voltage to a
regulated output voltage used by the loads for reliable operation. The buck converter is a high performance, fixed frequency (externally adjustable), synchronous buck PWM voltage-mode control. It drives integrated 45 m N-channel power MOSFETs saving board space and enhancing efficiency. The switching regulator output voltage is adjustable with an accuracy of less than 2.0 % to meet DDR requirements. Its output has the ability to track 1/2 the voltage applied at the VREFIN pin. The regulator's voltage control loop is compensated using a type III compensation network, with external components to allow for optimizing the loop compensation, for a wide range of operating conditions. A typical Bootstrap circuit with an internal PMOS switch is used to provide the voltage necessary to properly enhance the high-side MOSFET gate. The 34712 is designed to address DDR memory power supplies. The integrated converter has the ability to both sink and source up to 3.0 A of continuous current, making it suitable for bus termination power supplies.
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FUNCTIONAL DEVICE OPERATION OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
VIN < 3.0V SD = 0 & STBY = x SD = 1 & STBY = 0
Shutdown VTT = Discharge VREF = Discharge
PG = 1 SD = 1 & STBY = 1
Power Off VTT = OFF VREF = OFF
PG = 1 3.0V < = VIN < = 6.0V SD = 1 & STBY = 1
Standby VTT = OFF VREF = ON
PG = 1
VTT > VOV
Overvoltage VTT = ON VREF = ON
PG = 1
VTT < VOV
Normal VTT = ON VREF = ON
PG = 0
tTIMEOUT Expired
Short Circuit VTT = OFF VREF = OFF
PG = 1
IOUT > = ISHORT
VTT > VUV
tTIMEOUT Expired TJ < = 145C & tTIMEOUT Expired
VTT < VUV
Undervoltage VTT = ON VREF = ON
PG = 1
Thermal Shutdown VTT = OFF VREF = OFF
PG = 1
Over Current VTT = OFF VREF = ON
PG = 1
IOUT > = ILIM For > = 10ms
TJ > = 170C
Figure 6. Operation Modes Diagram
MODES OF OPERATION
The 34712 has three primary modes of operation: Normal Mode In normal mode, all functions and outputs are fully operational. To be in this mode, the VIN needs to be within its operating range, both Shutdown and Standby inputs are high, and no faults are present. This mode consumes the most amount of power. Standby Mode This mode is predominantly used in Desktop memory solutions where the DDR supply is desired to be ACPI compliant (Advanced Configuration and Power Interface). When this mode is activated by pulling the STBY pin low, VTT is put in High Z state, IOUT = 0 A, and VREF stays active. This is the S3 state Suspend-To-Ram or Self Refresh mode and it is the lowest DRAM power state. In this mode, the DRAM will preserve the data. While in this mode, the 34712 consumes less power than in the normal mode, because the buck converter and most of the internal blocks are disabled.
Shutdown Mode In this mode, activated by pulling the SD pin low, the chip is in a shutdown state and the outputs are all disabled and discharged. This is the S4/S5 power state or Suspend-ToDisk state, where the DRAM will loose all of its data content (no power supplied to the DRAM). The reason to discharge the VTT and VREF lines is to ensure upon exiting, the Shutdown Mode that VTT and VREF are lower than VDDQ, otherwise VTT can remain floating high, and be higher than VDDQ upon powering up. In this mode, the 34712 consumes the least amount of power since almost all of the internal blocks are disabled.
START-UP SEQUENCE
When power is first applied, the 34712 checks the status of the SD and STBY pins. If the device is in a shutdown mode, no block will power up and the output will not attempt to ramp. If the device is in a standby mode, only the VDDI internal supply voltage and the bias currents are established and no further activities will occur. Once the SD and STBY pins are released to enable the device, the internal VDDI POR signal is also released. The rest of the internal blocks will be enabled
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FUNCTIONAL DEVICE OPERATION PROTECTION AND DIAGNOSTIC FEATURES
and the buck converter switching frequency value is determined by reading the FREQ pin. A soft start cycle is then initiated to ramp up the output of the buck converter (VTT). The buck converter error amplifier uses the voltage on the VREFOUT pin (VREF) as its reference voltage. VREF is equal to 1/2 VDDQ, where VDDQ is applied to the VREFIN pin. This way, the 34712 assures that VREF and VTT voltages track 1/2 VDDQ to meet DDR requirements. Soft start is used to prevent the output voltage from overshooting during startup. At initial startup, the output capacitor is at zero volts; VOUT = 0 V. Therefore, the voltage across the inductor will be PVIN during the capacitor charge phase which will create a very sharp di/dt ramp. Allowing the inductor current to rise too high can result in a large difference between the charging current and the actual load current that can result in an undesired voltage spike once the capacitor is fully charged. The soft start is active each time
the IC goes out of standby or shutdown mode, power is recycled, or after a fault retry. To fully take advantage of soft starting, it is recommended not to enable the 34712 output before introducing VDDQ on the VREFIN pin. If this happens after a soft start cycle expires and the VREFIN voltage has a high dv/dt, the output will naturally track it immediately and ramp up with a fast dv/dt itself and that will defeat the purpose of soft starting. For reliable operation, it is best to have the VDDQ voltage available before enabling the output of the 34712. After a successful start-up cycle where the device is enabled, no faults have occurred, and the output voltage has reached its regulation point, the 34712 pulls the power good output signal low after a 10 ms reset delay, to indicate to the host that the device is in normal operation.
PROTECTION AND DIAGNOSTIC FEATURES
The 34712 monitors the application for several fault conditions to protect the load from overstress. The reaction of the IC to these faults ranges from turning off the outputs to just alerting the host that something is wrong. In the following paragraphs, each fault condition is explained: Output Overvoltage An overvoltage condition occurs once the output voltage goes higher than the rising overvoltage threshold (VOVR). In this case, the power good output signal is pulled high, alerting the host that a fault is present, but the VTT and VREF outputs will stay active. To avoid erroneous overvoltage conditions, a 20 s filter is implemented. The buck converter will use its feedback loop to attempt to correct the fault. Once the output voltage falls below the falling overvoltage threshold (VOVF), the fault is cleared and the power good output signal is pulled low, the device is back in normal operation. Output Undervoltage An undervoltage condition occurs once the output voltage falls below the falling undervoltage threshold (VUVF). In this case, the power good output signal is pulled high, alerting the host that a fault is present, but the VTT and VREF outputs will stay active. To avoid erroneous undervoltage conditions, a 20 s filter is implemented. The buck converter will use its feedback loop to attempt to correct the fault. Once the output voltage rises above the rising undervoltage threshold (VUVR), the fault is cleared and the power good output signal is pulled low, the device is back in normal operation. Output Over Current This block detects over current in the Power MOSFETs of the buck converter. It is comprised of a sense MOSFET and a comparator. The sense MOSFET acts as a current detecting device by sampling a ratio of the load current. That sample is compared via the comparator with an internal reference to determine if the output is in over current or not. If the peak current in the output inductor reaches the over current limit (ILIM), the converter will start a cycle-by-cycle operation to limit the current, and a 10 ms over current limit timer (tLIM) starts. The converter will stay in this mode of operation until one of the following occurs: * The current is reduced back to the normal level before tLIM expires, and in this case normal operation is regained. * tLIM expires without regaining normal operation, at which point the device turns off the output and the power good output signal is pulled high. At the end of a time-out period of 100 ms (tTIMEOUT), the device will attempt another soft start cycle. * The device reaches the thermal shutdown limit (TSDFET) and turns off the output. The power good output signal is pulled high. Short Circuit Current Limit This block uses the same current detection mechanism as the over current limit detection block. If the load current reaches the ISHORT value, the device reacts by shutting down the output immediately. This is necessary to prevent damage in case of a permanent short circuit. Then, at the end of a time-out period of 100 ms (tTIMEOUT), the device will attempt another soft start cycle. Thermal Shutdown Thermal limit detection block monitors the temperature of the device and protects against excessive heating. If the temperature reaches the thermal shutdown threshold (TSDFET), the converter output switches off and the power good output signal indicates a fault by pulling high. The device will stay in this state until the temperature has decreased by the hysteresis value and then After a time-out period (TTIMEOUT) of 100 ms, the device will retry automatically and the output will go through a soft start cycle. If successful normal operation is regained, the power good output signal is asserted low to indicate that.
34712
Analog Integrated Circuit Device Data Freescale Semiconductor
15
TYPICAL APPLICATIONS PROTECTION AND DIAGNOSTIC FEATURES
TYPICAL APPLICATIONS
VIN
BOOT BOOT C15 SW
I/O SIGNALS
4.7_nopop J2 R16 VIN GND PVIN 3 2 1
VIN VDDI VDDI
0.1uF
PVIN PVIN
C14 0.1uF
U1
23
22
20 PVIN
VDDI
J3 GND VMASTER VOUT
3 2 1
1
R11 10k FREQ
BOOT
PVIN
R12 10k_nopop FREQ
24
VIN
VIN
21
19
SGND FREQ N/C
MC34712
PVIN SW SW SW GND VREFOUT GND COMP VOUT GND INV
18
SW
2 3
17 16 15 14 13
GND SW
PG
PG STBY
4 5 6
VMASTER
VMASTER
PGOOD LED
SD VIN R7 1k
PG STBY SD
STBY
SD
R8 10k_nopop VREFIN R9 10k_nopop
7
VREFIN
8
9
10
11
VREFIN D1 LED VREFIN C11 C13 0.1uF LED VOUT VREFOUT VREFOUT C12 0.1uF INV COMP INV COMP VOUT 0.1uF
BUCK CONVERTER
VOUT1 L1 SW VOUT2 VOUT STBY
JUMPERS
J1 PVIN VMASTER LED
1
1.5uH D2 R3 4.7_nopop C9 1nF_nopop
2
1
C6 100uF C7 100uF C8 100uF
2
1 3 5 7 9
CON10A
2 4 6 8 10
VREFIN PG STBY SD
PMEG2010EA_nopop
1
SD
2
COMPENSATION NETWORK
VOUT
PVIN CAPACITORS
PVIN
OPTIONAL nopop
VDDI
12
C20 1nF INV C18 COMP 0.02nF R14 300 R1 20k
C1 0.1uF
C2 1uF
C3 100uF
C4 100uF
C5 100uF
FREQ R6 POT_50K_nopop
VIN CAPACITORS
VIN R2 12.7k_nopop C17 10uF C16 0.1uF
R15
C19 1.9nF
15k
34712
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Analog Integrated Circuit Device Data Freescale Semiconductor
TYPICAL APPLICATIONS PROTECTION AND DIAGNOSTIC FEATURES
COMPONENT SELECTION
SWITCHING FREQUENCY SELECTION The switching frequency defaults to a value of 1.0 MHz when the FREQ pin is grounded, and 200 KHz when the FREQ pin is connected to VDDI. Intermediate switching frequencies can be obtained by connecting an external resistor divider to the FREQ pin. The table below shows the resulting switching frequency versus FREQ pin voltage. Table 5. Switching Frequency Adjustment
FREQUENCY 200 253 307 360 413 466 520 573 627 680 733 787 840 893 947 1000 VOLTAGE APPLIED TO PIN FREQ 2.341 - 2.500 2.185 - 2.340 2.029 - 2.184 1.873 - 2.028 1.717 - 1.872 1.561 - 1.716 1.405 - 1.560 1.249 - 1.404 1.093 - 1.248 0.936 - 1.092
Inductor calculation is straight forward, being
where,
Maximum OFF time percentage
Switching period.
Drain - to - source resistance of FET
Winding resistance of Inductor
Output current ripple.
OUTPUT FILTER CAPACITOR
0.781 - 0.936 0.625 - 0.780 0.469 - 0.624 0.313 - 0.468 0.157 - 0.312 0.000 - 0.156
For the output capacitor, the following considerations are more important than the actual capacitance value, the physical size, the ESR and the voltage rating: Transient Response percentage, TR_% Maximum Transient Voltage, TR_v_dip = Vo*TR_% Maximum current step,
Inductor Current rise time,
where, D_max = Maximum ON time percentage. Figure 7. Resistor Divider for Frequency Adjustment IO = Rated output current. Vin_min = Minimum input voltage at PVIN As a result, it is possible to calculate
SELECTION OF THE INDUCTOR
34712
Analog Integrated Circuit Device Data Freescale Semiconductor
17
TYPICAL APPLICATIONS PROTECTION AND DIAGNOSTIC FEATURES
FSW
Gate Driver
In order to find the maximum allowed ESR,
PWM Comparitor SW L VOUT Error Amplifier
+ -
Ramp Generator
RS
INV
RO CO
VREFOUT
CS RF CX CF
+ -
The effects of the ESR is often neglected by the designers and may present a hidden danger to the ultimate supply stability. Poor quality capacitors have widely disparate ESR value, which can make the closed loop response inconsistent.
COMP
34712
Figure 9. Type III Compensation Network Consider the crossover frequency, FCROSS, of the open loop gain at one-sixth of the switching frequency, FSW. Then,
Io
Io_step
Current response
dt_I_rise
Worst case assumption
Figure 8. Transient Parameters
where RO is a user selected resistor. Knowing the LC frequency, it can be obtained the values of RF and CS:
TYPE III COMPENSATION NETWORK
Power supplies are desired to offer accurate and tight regulation output voltages. To accomplish this requires a high DC gain. But with high gain comes the possibility of instability. The purpose of adding compensation to the internal error amplifier is to counteract some of the gains and phases contained in the control-to-output transfer function that could jeopardized the stability of the power supply. The Type III compensation network used for 34712 comprises two poles (one integrator and one high frequency pole to cancel the zero generated from the ESR of the output capacitor) and two zeros to cancel the two poles generated from the LC filter as shown in Figure 9.
This gives as a result,
&
34712
18
Analog Integrated Circuit Device Data Freescale Semiconductor
TYPICAL APPLICATIONS PROTECTION AND DIAGNOSTIC FEATURES
Calculate Rs by placing the Pole 1 at the ESR zero frequency:
BOOTSTRAP CAPACITOR
The bootstrap capacitor is needed to supply the gate voltage for the high side MOSFET. This N-Channel MOSFET needs a voltage difference between its gate and source to be able to turn on. The high side MOSFET source is the SW node, so it is not ground and it is floating and moving in voltage, so we cannot just apply a voltage directly to the gate of the high side that is referenced to ground, we need a voltage referenced to the SW node. That is why the bootstrap capacitor is needed for. This capacitor charges during the high side off time, since the low side will be on during that time, so the SW node and the bottom of the bootstrap capacitor will be connected to ground and the top of the capacitor will be connected to a voltage source, so the capacitor will charge up to that voltage source (say 5V). Now when the low side MOSFET switches off and the high side MOSFET switches on, the SW nodes rises up to Vin, and the voltage on the boot pin will be Vcap + Vin. So the gate of the high side will have Vcap across it and it will be able to stay enhanced. A 0.1F capacitor is a good value for this bootstrap element.
Equating the Pole 2 at Crossover Frequency to achieve a faster response and a proper phase margin,
34712
Analog Integrated Circuit Device Data Freescale Semiconductor
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PACKAGING PACKAGING DIMENSIONS
PACKAGING
PACKAGING DIMENSIONS
EP SUFFIX 24 -PIN PLASTIC PACKAGE 98ARL10577D ISSUE B
34712
20
Analog Integrated Circuit Device Data Freescale Semiconductor
PACKAGING PACKAGING DIMENSIONS
EP SUFFIX 24 -PIN PLASTIC PACKAGE 98ARL10577D ISSUE B
34712
Analog Integrated Circuit Device Data Freescale Semiconductor
21
REVISION HISTORY
REVISION HISTORY
REVISION 1.0 2.0
DATE 2/2006 11/2006
DESCRIPTION OF CHANGES * * * * * * * * * * * * * * * * * * * * * * * * * * * Pre-release version Implemented Revision History page Initial release Converted format from Market Assessment to Product Preview Major updates to the data, form, and style Replaced all electrolytic capacitors with ceramic ones in Figure 1 Deleted Deadtime in Dynamic Electrical Characteristics Moved Figures 8 ahead of TYPE III COMPENSATION NETWORK Changed Features fom 2% to 1% Changed 34712 Simplified Application Diagram Removed Machine Model in Maximum Ratings Added minimum limits to Input DC Supply Current (11) Normal mode, Input DC Supply Current (11) Standby mode, and Input DC Supply Current (11) Shutdown mode Added High-side MOSFET Drain Voltage Range Changed Output Voltage Accuracy (12), (13), (14) Changed Short Circuit Current Limit Changed High-Side N-CH Power MOSFET (M3) RDS(ON) (12) and Low-Side N-CH Power MOSFET (M4) RDS(ON) (12) Changed M2 RDS(ON) Changed PVIN Pin Leakage Current Changed VREFOUT Buffered Reference Voltage Accuracy (17), VREFOUT Buffered Reference Voltage Current Capability, and VREFOUT Buffered Reference Voltage Over Current Limit Changed STBY Pin Internal Pull Up Resistor and SD Pin Internal Pull Up Resistor Changed Soft Start Duration, Over Current Limit Retry Time-out Period, and Output Undervoltage/ Overvoltage Filter Delay Timer Changed Oscillator Default Switching Frequency (18) Changed PG Reset Delay and Thermal Shutdown Retry Time-out Period (19) Changed drawings in Typical Applications Changed drawing in Type III Compensation Network Removed PC34712EP/R2 from the ordering information and added MC34712EP/R2 Changed the data sheet status to Advance Information
3.0
2/2007
4.0
5/2007
34712
22
Analog Integrated Circuit Device Data Freescale Semiconductor
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MC34712 Rev. 4.0 5/2007

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