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SI9176
New Product
Vishay Siliconix
High Performance Step-Down DC-DC Converter With Adjustable Output Voltage
FEATURES
D D D D D D D D D D D D D 2-MHz PWM Operation Integrated MOSFET Switches 2.6-V to 6.0-V Input Voltage Range Minimal Number of External Components Up to 96% conversion efficiency 600-mA Load Capability 100% Duty Cycle Allows Low Dropout Integrated Compensation Circuit Over-Current Protection Shutdown Current < 2 mA Thermal Shutdown Integrated UVLO 10-Pin MSOP and Space Saving MLP33 Packaging D User Selectable PWM, PSM, or AUTO Mode D PSM Frequency 20 kHz for Inaudible Harmonics
APPLICATIONS
D D D D D D D D D W-CDMA Cell Phone PDAs/Palmtop PCs LCD Modules Portable Image Scanners GPS Receivers Smart Phones MP3 Players 3G Cell Phone Digital Cameras
DESCRIPTION
The SI9176 is a high efficiency 600-mA step down converter with internal low on resistance power MOSFET switch and synchronous rectifier transistors. It is designed to convert one cell LiIon battery or three cell alkaline battery voltages to a dynamically adjustable dc output. The integrated high frequency error amplifier with internal compensation minimizes external components. 2-MHz switching permits use of small external inductor and capacitor sizes allowing one of the smallest solutions. PSM mode provides increased efficiency at light loads. In PSM mode the oscillator frequency is kept above 20 kHz to avoid audio band interference. When operating in Auto mode, the converter automatically selects operating in either PWM or PSM mode according to load current demand. The SI9176 is available in 10-pin MSOP and even smaller MLP33 packages and is specified to operate over the industrial temperature range of -40_C to 85_C.
In order to insure efficient conversion throughout the entire load range, PWM (pulse width modulation), PSM (pulse skipping mode) or Auto mode can be selected. In PWM mode,
TYPICAL APPLICATIONS CIRCUIT
BATTERY CIN 10 mF
VIN VDD LX
2.2 mH
VOUT
SI9176
PGND
COUT 4.7 mF
R1
FB ENABLE PWM/PSM/AUTO SD MODE REF AGND REF R2
Document Number: 71753 S-21825--Rev. A, 07-Oct-02
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SI9176
Vishay Siliconix
ABSOLUTE MAXIMUM RATINGS
Voltages Referenced to AGND = 0 V VIN, VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 V Lx, SD, MODE, FB, CREF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . --0.3 to 6.2 V (or to VDD +0.3 V whichever is less) GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . --0.3 to +0.3 V ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 kV Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . --65 to 125_C Operating Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150_C Power Dissipation (Package)a 10-pin MSOPb . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481 mW 10-pin MLP33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 915 mW Thermal Impedance (JA) 10-Pin MSOP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135_C/W 10-Pin MLP33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71_C/W Peak Inductor Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8 A Notes a. Device mounted with all leads soldered or welded to PC board. b. Derate 7.4 mW/_C above 85_C. c. Derate 14 mW/_C above 85_C.
New Product
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING RANGE
VIN Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 V to 5.5 V CIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 mF Ceramic COUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 mF Ceramic Inductor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 mH Operating Load Current PWM Mode . . . . . . . . . . . . . . . . . . . . . . 0 to 600 mA Operating Load Current PSM Mode . . . . . . . . . . . . . . . . . . . . . . . 0 to 150 mA
SPECIFICATIONS
Parameter Modef Symbol Test Conditions Unless Specified
--40_C to 85_C, VIN = VDD,, CIN = 10 mF, COUT = 4.7 mF L = 2.2 mH, 2.6 V VIN 5.5 V, R1 = 11.3 k, R2 = 20 k
Limits Mina Typb Maxa Unit
Under Voltage Lockout (UVLO)
Under Voltage Lockout (turn-on) Hysteresis VIN rising 2.3 0.1 2.5 V
Shutdown (SD)
Logic HIGH Logic LOW Delay to Outputc Pull Down VSDH VSDL ten ISD Settle Within 2% accuracy SD rising tr < 1 ms Input at VIN RL = 3.3 RL = 51 100 1.6 0.4 100 V ms mA
Mode Selection Tri-Level Logic (MODE)
MODE Pin HIGH MODE Pin LOW Mode Pin Input Current PWM Auto MODE = GND MODE = VIN --5 5 VIN --0.4 VIN 0.4 V mA
Oscillator
Frequency fOSC 1.6 2 2.4 MHz
Error Amplifier (FB Pin)
FB Voltage Accuracy Power Supply Rejection Input Bias Current VFB PSRR IFB VIN = 2.6 V to 5.5 VDC VFB = 1.25 V --1 TA = 25_C TA = --40 to 85_C 1.190 1.173 60 0.01 1 1.215 1.240 1.257 V db mA
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Document Number: 71753 S-21825--Rev. A, 07-Oct-02
SI9176
New Product
SPECIFICATIONS
Parameter Modef Converter Operation
Maximum Output Current Maximum Output Current Dropout Voltagee Closed Loop Bandwidth Load Regulationc Line Regulation PWM PSM PWM PSM IAUpk ILpk rDS( ) DS(on) VIN = 3 6 V 3.6 0.05 0 05 COUT(ESR) VIN = 3 6 V VOUT = 3 3 V 3.6 V, 3.3 IOUT 30 mA IOUT = 600 mA IOUT = 30 mA IOUT = 600 mA IOUT = 30 mA 20 PWM PSM ILOAD ILOAD VDD BW VIN = 3.6 V VOUT = 1.9 V @ 25_C IOUT = 30 mA to 600 mA IOUT = 30 mA to 75 mA VIN = 3.6 V VIN = 3.6 V VIN = 2.6 V, IOUT = 600 mA 190 300 0.5 0.25 0.1 0.1 200 1500 250 250 60 80 90 80 600 150 300 mA mA mV kHz % %/V mA m mVp-p % kHz
Vishay Siliconix
Test Conditions Unless Specified Symbol
--40_C to 85_C, VIN = VDD,, CIN = 10 mF, COUT = 4.7 mF L = 2.2 mH, 2.6 V VIN 5.5 V, R1 = 11.3 k, R2 = 20 k
Limits Mina Typb Maxa Unit
VOUT = 3 0 V VIN = 3 5 V to 5.5 V 3.0 V, 3.5 55
PWM/PSM Switch Threshold Current Maximum Inductor Peak Current Limit On Resistance Output Ripple Voltage Efficiency Frequency P-Channel N-Channel PWM PSM PWM PSM PSM
Supply Current
Input Supply Current Shutdown Supply Current PWM PSM ISUPPLY (VDD & VIN) ISD IOUT = 0 mA, VIN = 3 6 V (not switching, FB = GND) mA 3.6 switching SD = Low 450 400 2 750 mA
Thermal Shutdown
Thermal Shutdown Temperaturec Thermal Hysteresisc TJ(S/D) 165 20 _C
Notes a. The algebraic convention whereby the most negative value is a minimum and the most positive a maximum, is used in this data sheet. b. Typical values are for DESIGN AID ONLY, not guaranteed or subject to production testing. c. Guaranteed by design. d. Settling times, ts, apply after ten. e. Bypass is a device mode of operation, in which, the device is in 100% duty cycle. Bypass operation is possible in either PWM or PSM. f. Operating modes are controlled with the MODE pin where Auto mode = MODE = LOW, PWM Mode = MODE = HIGH, and PSM mode = MODE = OPEN.
Document Number: 71753 S-21825--Rev. A, 07-Oct-02
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SI9176
Vishay Siliconix
PIN CONFIGURATION
MSOP-10
LX AGND FB VDD REF
1 2 3 4 5 10 9 8 7 6
New Product
MLP33
PGND VIN AGND SD MODE LX AGND FB VDD REF 10 9 8 7 6 PGND VIN AGND SD MODE
2 3 4 5
Top View
Top View
PIN DESCRIPTION
Pin Number
1 2 3 4 5
Name
LX AGND FB VDD REF Inductor connection Low power analog ground Output voltage feedback Input supply voltage for the analog circuit.
Function
Internal reference, no connection should be made to this pin. Used to select switching mode of the buck converter PWM/PSM Pin Logic:
6
MODE
MODE Pin VIN Open GND
Operating Mode PWM PSM AUTO
7 8 9 10
SD AGND VIN PGND
Logic low disables IC and reduces quiescent current to below 2 mA Must be connected to AGND. Input supply voltage Low impedance power ground
ORDERING INFORMATION
MSOP-10 Part Number
SI9176DH-T1
MLP33 Temperature
--40 to 85_C
Marking
9176
Part Number
SI9176DM-T1
Marking
9176
Temperature
--40 to 85_C
Additional voltage options are available.
Eval Kit
SI9176DB
Temperature Range
--40 to 85_C
Board
Surface Mount
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Document Number: 71753 S-21825--Rev. A, 07-Oct-02
SI9176
New Product
FUNCTIONAL BLOCK DIAGRAM
Vishay Siliconix
VDD
SI9176
VIN
PMOS Current Sense Error Amplifier -+ Clamp -+
FB REF
PWM Comparator
PWM and Pulse Skipping Logic
LX
To IC Bias Voltage Reference, UVLO
2 MHz Oscillator
AGND
AGND
MODE
SD
PGND
DETAIL DESCRIPTION
General The SI9176 is a high efficiency synchronous dc-dc converter that is ideally suited for lithium ion battery or three cell alkaline applications, as well as step-down of 3.3-V or 5.0-V supplies. The major blocks of the SI9176 are shown in the Functional Block Diagram. The 0.25- internal MOSFETs switching at a frequency of 2-MHz minimize PC board space while providing high conversion efficiency and performance. The high frequency error-amplifier with built-in loop compensation minimizes external components and provides rapid output settling times of <30 ms. Sensing of the inductor current for control is accomplished internally without power wasting resistors. Start-Up When voltage is applied to VIN and VDD, the under-voltage lockout (UVLO) circuit prevents the oscillator and control circuitry from turning on until the voltage on the exceeds 2.4 V. With a typical UVLO hysteresis of 0.1 V, the converter operates continuously until the voltage on VIN drops below 2.3 V, whereupon the converter shuts down. This hysteresis prevents false start-stop cycling as the input voltage approaches the UVLO switching threshold. Start-up is always accomplished in PWM mode to ensure start-up under all load
Document Number: 71753 S-21825--Rev. A, 07-Oct-02
conditions. Switching to other modes of operation occurs according to the state of the MODE pin and the load current. The start-up sequence occurs after SD switches from LOW to HIGH with VIN applied, or after VIN rises above the UVLO threshold and SD is a logic HIGH. Mode Control (MODE) The MODE pin allows the user to control the mode of operation or to enable the SI9176 to automatically optimize the mode of operation according to load current. There are three different modes of operation as controlled by the MODE pin. Switching waveforms are shown in the Typical Switching Waveform sections, page 9. PWM Mode (MODE pin = HIGH) With the MODE pin in the logic HIGH condition, the SI9176 operates as a 2-MHz fixed frequency voltage mode converter. A NMOS synchronous rectification MOSFET transistor provides very high conversion efficiency for large load currents by minimizing the conduction losses. PWM mode provides low output ripple, fast transient response, and switching frequency synchronization. Output load currents can range from 0 to 600 mA.
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SI9176
Vishay Siliconix
New Product
currents, the converter operates in PSM mode to conserve power. The switchover threshold between the two modes is determined by the peak inductor current, which is 300 mA nominal. There is hysteresis in the switchover threshold to provide smooth operation. Thus, the mode PSM-to-PWM mode switchover current for increasing load currents is higher than that of PWM-to-PSM mode switchover for decreasing load currents. Oscillator The internal oscillator provides for a fixed 2-MHz switching frequency. Dynamic Output Voltage Control (REF) The SI9176 is designed with an adjustable output voltage which has a change of VFB to VIN -- VDROP. VOUT is defined according to the following relationship:
The error amplifier and comparator control the duty cycle of the PMOS MOSFET to continuously force the REF pin and FB pin voltages to be equal. As the input-to-output voltage difference drops, the duty cycle of the PMOS MOSFET can reach 100% to allow system designers to extract the maximum stored energy from the battery. The dropout voltage is 190 mV at 600 mA. During each cycle, the PMOS switch current is limited to a maximum of 1.5 A (typical) thereby protecting the IC while continuing to force maximum current into the load. Pulse Skipping Mode (MODE pin = OPEN) By leaving the MODE pin open-circuit, the converter runs in pulse skipping mode (PSM). In PSM mode the oscillator continues to operate, but switching only occurs if the FB pin voltage is below the REF voltage at the start of each clock cycle. Clock cycles are skipped thereby reducing the switching frequency to well below 100 kHz and minimizing switching losses for improved efficiency at loads under 150 mA. Although PSM mode switching frequency varies with line and load conditions, the minimum PSM frequency will be kept above 20 kHz for load currents of 30 mA or more to prevent switching noise from reaching the audio frequency range. Each time the PMOS switch is turned on, the inductor current is allowed to reach 300 mA. Once achieved, the PMOS switch is turned off and the NMOS switch is turned on in the normal manner. However, unlike PWM mode, the NMOS switch, turns off as the switch current approaches zero current to maximize efficiency. The PMOS switch remains on continuously (100% duty cycle) when the input-voltage-to-output-voltage difference is low enabling maximum possible energy extraction from the battery. PSM mode is recommend for load currents of 150 mA or less. Auto Mode When the MODE pin grounded, the converter is set to Auto mode. Switching between PWM mode and PSM modes takes place automatically without an external control signal. For heavy load operation, the converter will operate in PWM mode to achieve maximum efficiency. When delivering light load
VOUT =
1+ xV
R1 R2
FB
Converter Shutdown (SD pin) With logic LOW level on the SD pin, the SI9176 is shutdown. Shutdown reduces current consumption to less than 2-mA by shutting off all of the internal circuits. Both the PMOS and NMOS transistors are turned off. A logic HIGH enables the IC to start up as described in "Start-up" section. Thermal Shutdown The SI9176 includes thermal shutdown circuitry, which turns off the regulator when the junction temperature exceeds 165_C. Once the junction temperature drops below 145_C, the regulator is enabled. If the condition causing the over temperature, the SI9176 begins thermal cycling, turning the regulator on and off in response to junction temperature. Restart from a thermal shutdown condition is the same as described in the "Start-up" section.
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Document Number: 71753 S-21825--Rev. A, 07-Oct-02
SI9176
New Product
APPLICATIONS CIRCUIT
Vishay Siliconix
BATT
VIN C1 C2 VDD LX
2.2 mH
VOUT
CIN 10 mF
SI9176
PGND FB
COUT 4.7 mF
R1
ENABLE PWM/PSM/AUTO
SD MODE
REF AGND AGND
REF R2 CIN = 10 mF, Ceramic, Murata GRM42-2X5R106K16 C1, C2 = 0.01 mF, Vishay VJ0603Y 104KXXAT COUT = 4.7 mF, Ceramic, Murata GRM42-6X5R475K16 R1 = 8.2 k, Vishay CRCW06031132F R2 = 20 k, Vishay CRCW06032002F L = 2.2 mH, Toko A914BYW-2R2M
TYPICAL CHARACTERISTICS
VSDH SD tr VSDL tf
ten VOUT
Undefined (Load Dependent)
Time
d Indicates VOUT settles to 2% of the final value. Figure 1.
Document Number: 71753 S-21825--Rev. A, 07-Oct-02
PWM Mode VOUT Settling
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SI9176
Vishay Siliconix
TYPICAL CHARACTERISTICS
New Product
Auto Mode Efficiency vs. Load
100 VIN = 3.6 V 95 90 85 80 75 70 0 100 200 300 400 500 600 Load Current (mA) 0 0 VOUT = 1.9 V Dropout Voltage (mV) VOUT = 3.0 V 160 200
Dropout Voltage vs. ILOAD
VIN = 2.6 V VIN = 3.6 V
Efficiency (%)
120
80 VIN = 5.5 V 40
100
200
300
400
500
600
Load Current (mA)
PSM vs. PWM Efficiency
100 Efficiency (%) 95 90 85 80 75 0 100 200 300 400 500 600 Load Current (mA) VOUT Ripple (mVp-p) 80 PSM PSM 100 PWM
VOUT Ripple
VIN = 3.6 V VOUT = 1.9 V COUT = 4.7 mF
60
Auto Mode Efficiency vs. Load Direction
100 Efficiency (%) 95 90 85 80 75 0 100 200 300 400 500 600 Load Decreasing Load Increasing
40
20 PWM 0 0 30 60 90 120 150 Load Current (mA)
Load Current (mA)
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Document Number: 71753 S-21825--Rev. A, 07-Oct-02
SI9176
New Product
TYPICAL SWITCHING WAVEFORMS (VIN = 3.6 V, VOUT = 3.0 V)
PWM mode Heavy-Load Switching Waveforms, IOUT = 600 mA, MODE = HIGH PWM Mode Medium-Load Switching Waveforms, IOUT = 300 mA, MODE = HIGH
Vishay Siliconix
VLX, 5 V/div
VLX, 2 V/div
Inductor Current 500 mA/div
Inductor Current 500 mA/div
VOUT (AC-Coupled) 10 mV/div
VOUT (AC-Coupled) 10 mV/div
200 nS/div
200 nS/div
PWM Mode Light-Load Switching Waveforms, IOUT = 0 mA, MODE = HIGH
PSM Mode Light-Load Switching Waveforms, IOUT = 150 mA, MODE = OPEN
VLX, 5 V/div
VLX, 5 V/div
Inductor Current 200 mA/div
Inductor Current 200 mA/div
VOUT (AC-Coupled) 10 mV/div
VOUT (AC-Coupled) 10 mV/div
200 nS/div
1.0 mS/div
PSM Mode Light-Load Switching Waveforms, IOUT = 30 mA, MODE = OPEN
VLX, 5 V/div
Inductor Current 200 mA/div
VOUT (AC-Coupled) 100 mV/div
2.0 mS/div Document Number: 71753 S-21825--Rev. A, 07-Oct-02
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SI9176
Vishay Siliconix
New Product
TYPICAL WAVEFORMS (VIN = 3.6 V, VOUT = 1.9 V)
PWM Mode Heavy-Load Switching Waveforms, IOUT = 600 mA, MODE = HIGH PWM Mode Medium-Load Switching Waveforms, IOUT = 300 mA, MODE = HIGH
VLX, 5 V/div Inductor Current 500 mA/div
VLX, 5 V/div
Inductor Current 500 mA/div
VOUT (AC-Coupled) 10 mV/div
VOUT (AC-Coupled) 10 mV/div
200 nS/div
200 nS/div
PWM Mode Light-Load Switching Waveforms, IOUT = 0 mA, MODE = HIGH
PSM Mode Light-Load Switching Waveforms, IOUT = 150 mA, MODE = OPEN
VLX, 5 V/div
VLX, 5 V/div
Inductor Current 200 mA/div
Inductor Current 200 mA/div
VOUT (AC-Coupled) 10 mV/div
VOUT (AC-Coupled) 100 mV/div
200 nS/div
1.0 mS/div
PSM Mode Light-Load Switching Waveforms, IOUT = 30 mA, MODE = OPEN
VLX, 5 V/div
Inductor Current 200 mA/div VOUT (AC-Coupled) 100 mV/div
2.0 mS/div
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Document Number: 71753 S-21825--Rev. A, 07-Oct-02
SI9176
New Product
Vishay Siliconix
TYPICAL START-UP AND SHUTDOWN TRANSIENT WAVEFORMS (VIN = 3.6 V, VOUT = 1.9 V)
Start-Up, RLOAD = 4 Start-Up, VIN = VSD = 3.6 V, RLOAD = 4
VIN, VSD, 1 V/div VSD, 1 V/div
VOUT, 500 mV/div VOUT, 500 mV/div
20 mS/div
20 mS/div
Shutdown, RLOAD = 4
Enable Switching, RLOAD = 4
VSD, 1 V/div
VSD 1 V/div
VOUT, 500 mV/div
VOUT, 500 mV/div
200 mS/div
20 mS/div
TYPICAL MODE SWITCH TRANSIENT WAVEFORM
Output Transient At Mode Switch, ILOAD = 30 mA
VOUT (AC-Coupled) 200 mV/div
Mode Pin 1 V/div
100 mS/div Document Number: 71753 S-21825--Rev. A, 07-Oct-02 www.vishay.com
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SI9176
Vishay Siliconix
New Product
TYPICAL LOAD TRANSIENT WAVEFORMS (VIN = 3.6 V, VOUT = 1.9 V)
Load Transient, Auto Mode, ILOAD = 30 to 500 mA, MODE = LOW Load Transient, PWM Mode, ILOAD = 30 to 500 mA, L = 2.2 mH, MODE= HIGH
ILOAD, 200 mA /div
ILOAD, 200 mA /div
VOUT (AC-Coupled) 50 V/div 10 mS/div 10 mS/div
VOUT (AC-Coupled) 50 mV/div
Load Transient (PSM Mode), ILOAD = 30 to 150 mA, L = 2.2 mH
ILOAD, 200 mA /div
VOUT (AC-Coupled) 50 mV/div
100 mS/div
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Document Number: 71753 S-21825--Rev. A, 07-Oct-02

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