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F72820
F72820
Synchronous Buck PWM DC-DC Controller
Release Date: July, 2007 Version: V0.24P
Jul 2007 V0.24P
F72820
F72820 Datasheet Revision History
Version 0.21P 0.22P 0.23P 0.24P Date Mar/2005 Jun/2005 Mar/2006 Jul 2007 14 15 13 Page Revision History Preliminary version Update application circuit Correct application circuit Update company address
Please note that all data and specifications are subject to change without notice. All the trade marks of products and companies mentioned in this data sheet belong to their respective owners.
LIFE SUPPORT APPLICATIONS These products are not designed for use in life support appliances, devices, or systems where malfunction of these products can reasonably be expected to result in personal injury. Customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Fintek for any damages resulting from such improper use or sales.
Jul 2007 V0.24P
F72820 Table of Content
1. 2. 3. 4. 5. 6. General Description ..................................................................................................................... 1 Feature List .................................................................................................................................. 1 Pin Configuration ......................................................................................................................... 2 Block Diagram.............................................................................................................................. 2 Pin Description ............................................................................................................................. 3 Function Description .................................................................................................................... 4 6.1 Bootstrap Operation ................................................................................................................. 4 6.2 Dual Power Operation.............................................................................................................. 4 6.3 Soft-Start .................................................................................................................................. 5 6.4 Over-current Protection............................................................................................................ 5 6.5 Under-voltage Protection ......................................................................................................... 6 6.6 Output Voltage Selection.......................................................................................................... 7 6.7 Converter Shut Down............................................................................................................... 7 6.8 PWM Controller Feedback Compensation............................................................................... 7 6.9 Typical Characteristic ............................................................................................................... 9 7. 8. 9. 10. Electrical Characteristic.............................................................................................................. 11 Ordering Information .................................................................................................................. 12 Package Dimensions (8-SOP/150 mil)....................................................................................... 13 Application Circuit ...................................................................................................................... 14
Jul 2007 V0.24P
F72820 1. General Description
The F72820 is a single PWM DC-DC converter controller for application requiring high current such as motherboard, graphic card etc. The F72820 uses voltage mode PWM controller with fast transient response (driving two external N-channel MOSFETs in a synchronous rectified buck converter topology) and integrates some functions such as soft-start, over current and short circuit protections etc. Over current protection is achieved by monitoring the voltage drops across the high side MOSFET without the need for a current sensing resistor and short circuit condition is detected through FB pin. If fault conditions occur, the F72820 will initiate the soft start cycle. After three cycles and the fault conditions persist, the controller will go into shut down status. In shut down status, both gate drive signals will be low. To restart the controller, either recycling the Vcc supply or momentarily pulling OCSET pin below 1.25V. The F72820 is available in 8-SOP package.
2. Feature List
Provides one synchronous rectified buck DC-DC PWM controller Fast transient response (high bandwidth error amplifier; full 0~100% duty cycle) Fixed operation frequency : 300KHz Single loop voltage-mode control Few external components Output range adjustable down to 0.8V Operation is under 5V input Drives external N-channel MOSFETs Over current monitor is used by MOSFET RDS(ON) 0.8V internal reference voltage 2% accuracy over line, load and temperature Internal soft-start (typically 3 ms) Internal loop compensation Under voltage fault monitoring and protection Over voltage protection 8-SOP package (150 mil)
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Jul 2007 V0.24P
F72820 3. Pin Configuration
BOOT UGATE GND LGATE 1 2 3 4 8 7 6 5 PHASE OCSET FB VCC
F72820
4. Block Diagram
VCC
Regulator
BOOT
Reference Voltage
Bias & SS
Power On Reset 40uA
1.1V OVP
OCSET
OCP UVP
Control Logic PHASE UGATE
Comp VCC
0.5V 0.8V
Error Amp
FB
GND
300KHz Tri-OSC
LGATE
Figure 1: Block Diagram
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F72820
VIN BOOT 5V Q1 PWM CONTROLLER Q2 VOUT
Figure 2: Simplified power system diagram
5. Pin Description
AIN AOUT P - Input pin(Analog) - Output pin(Analog) - Power
Pin No 1
Pin Name BOOT
TYPE P
PWR
Description Provide ground reference voltage for high side MOSFET by bootstrap circuit or ATX 12V.
2
UGATE
AOUT
BOOT
Higher gate drive output. Connect this pin to gate of the high side MOSFET
3 4
GND LGATE
P AOUT VCC
Power ground pin for the chip Lower gate drive output. Connect this pin to gate of the low side MOSFET
5 6
VCC FB
P AIN VCC
IC supply voltage. This voltage is monitored for power-on-reset purpose. Inverting input of the error amplifier used to compensate the feedback loop of the PWM controller.
7
OCSET/SD
AOUT/AIN
VCC
This is multi-function pin. Connecting a resistor from this pin to drain of high side MOSFET and an internal 40uA current source to ground. OCSET voltage is reference for over current detect. When OCSET voltage is under 1.25V, shut down function will be enabled.
8
PHASE
AIN
VCC
Connect to high side MOSFET source and monitor its voltage drop for over current protection.
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Jul 2007 V0.24P
F72820 6. Function Description
The F72820 is a single PWM DC-DC converter controller for application requiring high current such as motherboard, graphic card etc. The F72820 uses voltage mode PWM controller with fast transient response (driving two external N-channel MOSFETs in a synchronous rectified buck converter topology) and integrates some functions such as soft-start, over current and short circuit protections etc. Over current protection is achieved by monitoring the voltage drop across the high side MOSFET, eliminating the need for a current sensing resistor and short circuit condition is detected through the FB pin. If fault conditions occur, the F72820 would initiate the soft start cycle. After three cycles and the fault condition persist, the controller will go into shut down status. In shut down, both gate drive signals will be low. To restart the controller, either recycle the Vcc supply or momentarily pull the OCSET pin below 1.25V.
6.1 Bootstrap Operation
In single power supply system, the UGATE is powered by an external bootstrap circuit as Fig 3. The Boot capacitor, CBOOT is charged and generated a floating reference voltage at phase pin. Typically a 0.1uF CBOOT is enough for the most of applications. The CBOOT capacitor is refreshed and charged to a voltage of "VCC - Diode Drop" while low side power MOS turning on.
5V
VCC
BOOT UGATE
Q1 VOUT
PHASE LGATE
Q2
Fig 3. Single 5V Power Supply Operation.
6.2 Dual Power Operation
The F72820 Power-on-reset monitors VCC supply voltage and input voltage at the OCSET pin. POR level is 3.8V with 0.5V hysteresis at VCC voltage and 1.25V at OCSET voltage, The POR function initiates soft-start operation and reset control logic after these supply voltages exceed their POR threshold voltages.
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Jul 2007 V0.24P
F72820
VCC Regulator BOOT 12V 5V UGATE Q1 VOUT
PHASE LGATE
Q2
Figure 4
6.3 Soft-Start
The POR function initiates the digital soft-start sequence; the soft start function is used to prevent surge current from power supply input during power on. When soft start event, PWM error amplifier reference inputs are forced to track a voltage level proportional to the soft-start voltage. As the soft-start voltage slews up, the PWM comparator regulates the output relative to the tracked soft-start voltage, slowly charging the output capacitor(s), the soft start duration is 3mS in typical case.
6V
VCC
3V VOUT 0V
3mS
TIME
Figure 5
6.4 Over-current Protection
The over current protection function of the F72820 is trigger when the voltage across the RDS (ON) of upper side MOSFET the developed by drain current exceeds over-current tripping level. An external resistor (ROCSET) programs the over-current tripping level of the PWM converter. As show on Figure 6, the internal 40uA current sink develops a voltage across ROCSET that is reference to VIN. The over current comparator detect over current event when UGATE is high and PHASE voltage is under OCSET voltage. When OC be detected, over current protect function will soft start three times and check over current again. If over current event is true, the F72820 will be shut down.
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Jul 2007 V0.24P
F72820
OVER-CURRENT TRIP: VDS > VSET I D x R DS(ON) > I OCSET x R OCSET V PHASE = VIN V OCSET = VIN
-
VDS VSET OCSET
I OCSET
R OCSET
VSET iD
VIN = 5V
BOOT
40uA
UGATE OC Q1 PHASE LGATE Q2
VDS
VOUT
Figure 6
6.5 Under-voltage Protection
Pins FB are monitored during converter operation by under-voltage (UV) comparators. If the FB voltage drops below 0.5V, a fault signal is generated. The internal fault logic shut down regulator simultaneously when the fault signal triggers a restart. At time t0, VOUT has dropped below 0.5V of the nominal output voltage. Output is quickly shut down and the internal soft-start function begins producing soft-start ramps. The delay interval, t0 to 3*tss, seen by the output is equivalent to three soft-start cycles. After a short delay interval of 10.5ms, the fourth internal soft-start cycle initiates a normal soft-start ramp of the output, at time 3*tss. Both outputs are brought back into regulation by time 4*tss, as long as the UV event has cleared. When the cause of the UV still been present after the delay interval. A fault signal could then be generated and the outputs once again shutdown.
3V
1.5V
VOUT
0V
t0
tss
2tss
3tss
4tss
TIME
Delay interval
Figure 7
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Jul 2007 V0.24P
F72820
6.6 Output Voltage Selection
The output voltage of the PWM converter can be programmed to any level between VIN (i.e. 5+V) and the internal reference, 0.8V. An external resistor divider is used to scale the output voltage relative to the reference voltage and feed it back to the inverting input of the error amplifier, see Figure 8. Depending on the value chosen for R1 (the resistor connected between VOUT1 and FB), R4 (the resistor connected from FB to GND) can be calculated based on the following equation:
R4 =
R1x 0.8V VOUT - 0.8V
(EQ1)
If the desired output voltage is 0.8V, simply route VOUT back to FB through R1, but do not populate R4.
5V
VCC
BOOT UGATE PHASE LGATE
Q1 VOUT
Q2 R1 R4
FB
Figure 8: Output voltage selection
6.7 Converter Shut Down
Pulling low the OCSET pin by a small signal transistor can shutdown the F72820 PWM controller as show is typical application circuit.
6.8 PWM Controller Feedback Compensation
The F72820 is a voltage mode step down PWM controller. The gain of error amp is fixed at 34dB for simplified design and saving external components. The amplitude of internal Tri-wave OSC is 1.75V. The loop gain and loop Zero/Pole are calculated as follow equations.
F72820
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Jul 2007 V0.24P
F72820
DC_Loop_Ga in = 34dB x Pole_of_LC _Filter = 5 0.8 x 1.8 Vout 1 2 LC Pole_of_EA = 130kHz Zero_of_Ou tput_Cap_E SR = 1 2 x ESR x C
VIN UGATE Error Amp L comp LGATE
1.75V
VREF
VOUT ESR C
The F72820 Bode plot as shown Figure 9
Gain ( dB ) Cout=1000u ( ESR=30m ) Lout=4.7u Vout=1.6V Pole of LC Filter Zero of Cout ESR
40 30 20 10
Pole of EA 0.1k 1k 10k 100k 1M
f ( Hz )
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Jul 2007 V0.24P
F72820
6.9 Typical Characteristic
Dead time Dead time
UGATE
UGATE
LGATE
LGATE
Power up
Power off
UGATE
UGATE
OCSET OCSET FB VOUT VOUT
FB
Load transient response
UGATE
Load transient response
UGATE LGATE UGATE VOUT
VOUT
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Jul 2007 V0.24P
F72820
Bootstrap Wave Form Over-Current Protect
UGATE UGATE LGATE LGATE BOOT OCSET PHASE VOUT
Reference VS Temperature 794.8 Reference (mV) 794.6 794.4 794.2 794 793.8 25 35 45 55 65 75 85 Temperature ()
Iocset (uA) 42.5 42 41.5 41 40.5 40
Iocset VS. Temperature
25 35 45 55 65 75 85 Temperature ()
Oscillator Frequency VS. Temperature 316 314 312 310 308 306 304 302 25 35 45 55 65 75 85 Temperature ()
F72820
Frequency (kHz)
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Jul 2007 V0.24P
F72820 7. Electrical Characteristic
Absolute Maximum Ratings
PARAMETER
IC supply voltage Gate drivers supply voltage PWM controller outputs Feedback voltages of both regulators ESD classification Maximum junction temperature (plastic package) Maximum storage temperature Maximum lead temperature (soldering 10s)
SYMBOL
VCC 12VCC UGATE, LGATE FB, FB2, COMP HBM Tj TSTO
RATINGS
7 15
UNIT
V V V
GND - 0.3-17 2 150 -65 ~ 150 260
V kV C C C
Note: If ICs are stressed beyond the limits listed in the "absolute maximum ratings", they may be permanently destroyed. These are stress ratings only and functional operation of the device at these or any other condition beyond those indicated under "recommended operating conditions" is not implied. Exposure to absolute maximum rated conditions for extended periods may affect device reliability.
Package thermal information
PARAMETER
Thermal resistance junction-ambient
SYMBOL
Rth_ja
SOIC
133
UNIT
C/W
DC and AC electrical characteristics
PARAMETER SYMBOL TEST CONDITIONS MIN. TYP. MAX. UNIT
VCC SUPPLY CURRENT/Regulated Voltage Nominal supply current 5VCC Regulated Voltage from BOOT POWER-ON RESET Rising VCC threshold Falling VCC threshold Rising VOCSET Threshold OSCILLATOR AND Protection Free running frequency Ramp Amplitude FB Over Voltage Trip FOSC VOSC FB Rising 1.0 VCC=5V 250 300 1.75 1.1
*
ICC VCC
UGATE, LGATE and DRIVE2 open VBOOT = 12V 5.0
2 5.5
4 6
mA V
VOCSET = 4.5V VOCSET1 = 4.5V 3.1 0.8
3.8 3.3 1.25
4.0
V V
2.0
V
350
kHz VP-P
1.2
V
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Jul 2007 V0.24P
F72820
PARAMETER
FB Under Voltage Trip OCSET Current Source Soft-start interval REFERENCE VOLTAGE Reference voltage PWM CONTROLLER GATE DRIVERS Upper Drive Source Upper Drive Sink Lower Drive Source Lower Drive Sink Error Amplifier DC Gain Note: Design Guarantee 34
*
SYMBOL
TEST CONDITIONS
FB Falling
MIN.
0.4 35 1
TYP.
0.5 40 3
MAX.
0.6 45 6
UNIT
V uA ms
IOCSET TSS
VOCSET = 4.5V
VREF
0.784
0.8
0.816
V
RUGATE RUGATE RLGATE RLGATE
BOOT = 12V ; BOOT - VUGATE = 1V VUGATE = 1V VCC - VLGATE = 1V VLGATE = 1V
8 4 3 2
12 6 4.5 3

dB
8. Ordering Information
Part Number F72820 SG Package Type 8-SOP (Green Package) Production Flow Commercial, 0C to +70C
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Jul 2007 V0.24P
F72820 9. Package Dimensions (8-SOP/150 mil)
8 5
c
E
HE
L
1
D
4
0.25 O
A Y SEATING PLANE b e A1 GAUGE PLANE
Control demensions are in milmeters .
SYMBOL A A1 b c E D e HE Y L DIMENSION IN MM MIN. MAX. 1.35 1.75 0.10 0.25 0.33 0.51 0.19 0.25 3.80 4.00 4.80 5.00 1.27 BSC 6.20 5.80 0.10 0.40 1.27 0 10 DIMENSION IN INCH MIN. MAX. 0.053 0.069 0.010 0.004 0.013 0.020 0.008 0.010 0.150 0.157 0.188 0.196 0.050 BSC 0.228 0.016 0 0.244 0.004 0.050 10
Feature Integration Technology Inc.
Headquarters 3F-7, No 36, Tai Yuan St., Chupei City, Hsinchu, Taiwan 302, R.O.C. TEL : 886-3-5600168 FAX : 886-3-5600166 www: http://www.fintek.com.tw Taipei Office Bldg. K4, 7F, No.700, Chung Cheng Rd., Chungho City, Taipei, Taiwan 235, R.O.C. TEL : 866-2-8227-8027 FAX : 866-2-8227-8037
Please note that all datasheet and specifications are subject to change without notice. All the trade marks of products and companies mentioned in this datasheet belong to their respective
F72820
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Jul 2007 V0.24P
F72820 10. Application Circuit
14
F72820
15

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