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MAX8792ETD+-MAX8792ETD+T
Single Quick-PWM Step-Down Controller with Dynamic REFIN
General DescriptionThe MAX8792 pulse-width modulation (PWM) controller
provides high efficiency, excellent transient response,
and high DC-output accuracy needed for stepping
down high-voltage batteries to generate low-voltage
core or chipset/RAM bias supplies in notebook comput-
ers. The output voltage can be dynamically controlled
using the dynamic REFIN, which supports input volt-
ages between 0 to 2V. The REFIN adjustability com-
bined with a resistive voltage-divider on the feedback
input allows the MAX8792 to be configured for any out-
put voltage between 0 to 0.9VIN.
Maxim’s proprietary Quick-PWM™ quick-response, con-
stant-on-time PWM control scheme handles wide
input/output voltage ratios (low-duty-cycle applications)
with ease and provides 100ns “instant-on” response to
load transients while maintaining a relatively constant
switching frequency. Strong drivers allow the MAX8792
to efficiently drive large synchronous-rectifier MOSFETs.
The controller senses the current across the synchro-
nous rectifier to achieve a low-cost and highly efficient
valley current-limit protection. The adjustable current-
limit threshold provides a high degree of flexibility,
allowing thermally compensated protection using an
NTC or foldback current-limit protection using a volt-
age-divider derived from the output.
The MAX8792 includes a voltage-controlled soft-start
and soft-shutdown in order to limit the input surge cur-
rent, provide a monotonic power-up (even into a
precharged output), and provide a predictable power-
up time. The controller also includes output fault protec-
tion—undervoltage and overvoltage protection—as well
as thermal-fault protection.
The MAX8792 is available in a tiny 14-pin, 3mm x 3mm
TDFN package. For space-constrained applications,
refer to the MAX17016 single step-down with 10A, 26V
internal MOSFETs available in a small 40-pin, 6mm x
6mm TQFN package.
ApplicationsNotebook Computers
I/O and Chipset Supplies
GPU Core Supply
DDR Memory—VDDQ or VTT
Point-of-Load Applications
Step-Down Power Supply
FeaturesQuick-PWM with Fast Transient ResponseSupports Any Output Capacitor
No Compensation Required with
Polymers/Tantalum
Stable with Ceramic Output Capacitors Using
External CompensationPrecision 2V ±10mV ReferenceDynamically Adjustable Output Voltage
(0 to 0.9VINRange)
Feedback Input Regulates to 0 to 2V REFIN
Voltage
0.5% VOUTAccuracy Over Line and Load26V Maximum Input Voltage RatingAdjustable Valley Current-Limit Protection
Thermal Compensation with NTC
Supports Foldback Current LimitResistively Programmable Switching FrequencyOvervoltage ProtectionUndervoltage/Thermal ProtectionVoltage Soft-Start and Soft-ShutdownMonotonic Power-Up with Precharged OutputPower-Good Window Comparator
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFINMAX8792
GND
TDFN
(3mm x 3mm)TOP VIEW51110
REFREFIN
PGOOD
ILIM
BST
TON
SKIP
Pin Configuration
Ordering Information19-0739; Rev 1; 2/10
Note:This device is specified over the -40°C to +85°C operating
temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
EVALUATION KIT
AVAILABLE
PARTPIN-PACKAGEPKG
CODE
TOP
MARKMAX8792ETD+T14 TD FN - E P * 3m m x 3m m T1433-1ADC
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(Circuit of Figure 1, VIN= 12V, VDD= VCC= VEN= 5V, REFIN = ILIM = REF, SKIP= GND. TA= 0°C to +85°C, unless otherwise spec-
ified. Typical values are at TA= +25°C.) (Note 1)
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.
TON to GND...........................................................-0.3V to +28V
VDDto GND..............................................................-0.3V to +6V
VCCto GND................................................-0.3V to (VDD+ 0.3V)
EN, SKIP, PGOOD to GND.......................................-0.3V to +6V
REF, REFIN to GND....................................-0.3V to (VCC + 0.3V)
ILIM, FB to GND.........................................-0.3V to (VCC+ 0.3V)
DL to GND..................................................-0.3V to (VDD+ 0.3V)
BST to GND.................................................(VDD- 0.3V) to +34V
BST to LX..................................................................-0.3V to +6V
BST to VDD.............................................................-0.3V to +28V
DH to LX....................................................-0.3V to (VBST+ 0.3V)
REF Short Circuit to GND...........................................Continuous
Continuous Power Dissipation (TA= +70°C)
14-Pin 3mm x 3mm TDFN
(derated 24.4mW/°C above +70°C)....................1951mW
Operating Temperature Range (extended).........-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature.........................................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
Soldering Temperature (reflow).......................................+240°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
PWM CONTROLLERInput Voltage RangeVIN226V
Quiescent Supply Current (VDD)IDD + ICCFB forced above REFIN0.71.2mA
Shutdown Supply Current (VDD)ISHDNEN = GND, TA = +25°C0.12μA
VDD-to-VCC ResistanceRCC20Ω
RTON = 97.5kΩ (600kHz)118139160
RTON = 200kΩ (300kHz)250278306On-TimetON
VIN = 12V,
VFB = 1.0V
(Note 3)RTON = 302.5kΩ (200kHz)354417480
Minimum Off-TimetOFF(MIN)(Note 3)200300ns
TON Shutdown Supply CurrentEN = GND, VTON = 26V,
VCC = 0V or 5V, TA = +25°C0.011μA
REFIN Voltage RangeVREFIN(Note 2)0VREFV
FB Voltage RangeVFB(Note 2)0VREFV
TA = +25°C0.4950.50.505VREFIN = 0.5V,easur ed at FB,I N = 2V to 26V ,
SKIP = VDD
TA = 0°C to +85°C0.4930.507
TA = +25°C0.9951.01.005VREFIN = 1.0VTA = 0°C to +85°C0.9931.007
FB Voltage AccuracyVFB
VREFIN = 2.0VTA = 0°C to +85°C1.9902.02.010
FB Input Bias CurrentIFBVFB = 0.5V to 2.0V, TA = +25°C-0.1+0.1μA
Load-Regulation ErrorILOAD = 0 to 3A, SKIP = VDD0.1%
Line-Regulation ErrorVCC = 4.5V to 5.5V, VIN = 4.5V to 26V0.25%
Soft-Start/-Stop Slew RatetSSRising/falling edge on EN1mV/μs
Dynamic REFIN Slew RatetDYNRising edge on REFIN8mV/μs
REFERENCENo load1.9902.002.010Reference VoltageVREFVCC = 4.5V
to 5.5VIREF = -10μA to +50μA1.982.02V
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
FAULT DETECTIONWith respect to the internal target voltage
(error comparator threshold); rising edge;
hysteresis = 50mV
250300350mV
Dynamic transitionVREF +
Output Overvoltage-Protection
Trip ThresholdOVP
Minimum OVP threshold0.7
Output Overvoltage
Fault-Propagation DelaytOVPFB forced 25mV above trip threshold5μs
Output Undervoltage-Protection
Trip ThresholdUVP
With respect to the internal target voltage
(error comparator threshold); falling edge;
hysteresis = 50mV
-240-200-160mV
Output Undervoltage
Fault-Propagation DelaytUVPFB forced 25mV below trip threshold100200350μs
UVP falling edge, 25mV overdrive5
OVP rising edge, 25mV overdrive5PGOOD Propagation DelaytPGOOD
Startup delay100200350
PGOOD Output-Low VoltageISINK = 3mA0.4V
PGOOD Leakage CurrentIPGOODFB = REFIN (PGOOD high impedance),
PGOOD forced to 5V, TA = +25°C1μA
Dynamic REFIN Transition Fault
Blanking Threshold
Fault blanking initiated; REFIN deviation
from the internal target voltage (error
comparator threshold); hysteresis = 10mV
±50mV
Thermal-Shutdown ThresholdTSHDNHysteresis = 15°C160°C
VCC Undervoltage Lockout
ThresholdV U V LO( V C C ) Rising edge, PWM disabled below this
level; hysteresis = 100mV3.954.24.45V
CURRENT LIMITILIM Input Range0.4VREFV
VILIM = 0.4V182022Current-Limit ThresholdVILIMITILIM = REF (2.0V)92100108mV
Current-Limit Threshold
(Negative)VINEGVILIM = 0.4V-24mV
Current-Limit Threshold
(Zero Crossing)VZXVILIM = 0.4V,
VGND - VLX, SKIP = GND or open1mV
Ultrasonic FrequencySKIP = open (3.3V); VFB = VREFIN + 50mV1830kHzl tr asoni c C ur r ent- Li m i t Thr eshol d SKIP = open (3.3V); VFB = VREFIN + 50mV35mV
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Figure 1, VIN= 12V, VDD= VCC= VEN= 5V, REFIN = ILIM = REF, SKIP= GND. TA= 0°C to +85°C, unless otherwise spec-
ified. Typical values are at TA= +25°C.) (Note 1)
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Figure 1, VIN= 12V, VDD= VCC= VEN= 5V, REFIN = ILIM = REF, SKIP= GND. TA= 0°C to +85°C, unless otherwise spec-
ified. Typical values are at TA= +25°C.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GATE DRIVERSLow state (pulldown)1.23.5DH Gate Driver On-ResistanceRON(DH)BST - LX forced to 5VHigh state (pullup)1.23.5Ω
High state (pullup)1.74DL Gate Driver On-ResistanceRON(DL)Low state (pulldown)0.92Ω
DH Gate Driver Source/
Sink CurrentIDHDH forced to 2.5V, BST - LX forced to 5V1.5A
DL Gate Driver Source CurrentID L(S OU RC E ) DL forced to 2.5V1A
DL Gate Driver Sink CurrentIDL(SINK)DL forced to 2.5V2.4A
DH low to DL high1025Driver Propagation DelayDL low to DH high1535ns
DL falling, CDL = 3nF20DL Transition TimeDL rising, CDL = 3nF20ns
DH falling, CDH = 3nF20DH Transition TimeDH rising, CDH = 3nF20ns
Inter nal BS T S w i tch On- Resi stanceRBSTIBST = 10mA, VDD = 5V47Ω
INPUTS AND OUTPUTSEN Logic-Input ThresholdVENEN rising edge, hysteresis = 450mV (typ)1.201.72.20V
EN Logic-Input CurrentIENEN forced to GND or VDD, TA = +25°C-0.5+0.5μA
High (5V VDD)VCC -
Mid (3.3V)3.03.6
Ref (2.0V)1.72.3
SKIP Quad-Level Input Logic
LevelsVSKIP
Low (GND)0.4
SKIP Logic-Input CurrentISKIPSKIP forced to GND or VDD-2+2μA
ELECTRICAL CHARACTERISTICS(Circuit of Figure 1, VIN= 12V, VDD= VCC= VEN= 5V, REFIN = ILIM = REF, SKIP= GND. TA= -40°C to +85°C, unless otherwise
specified.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
PWM CONTROLLERInput Voltage RangeVIN226V
Quiescent Supply Current (VDD)IDD + ICCFB forced above REFIN1.2mA
RTON = 97.5kΩ (600kHz)115163
RTON = 200kΩ (300kHz)250306On-TimetON
VIN = 12V,
VFB = 1.0V
(Note 3)RTON = 302.5kΩ (200kHz)348486
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Figure 1, VIN= 12V, VDD= VCC= VEN= 5V, REFIN = ILIM = REF, SKIP= GND. TA= -40°C to +85°C, unless otherwise
specified.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINMAXUNITSMinimum Off-TimetOFF(MIN)(Note 3)350ns
REFIN Voltage RangeVREFIN(Note 2)0VREFV
FB Voltage RangeVFB(Note 2)0VREFV
VREFIN = 0.5V0.490.51
VREFIN = 1.0V0.991.01FB Voltage AccuracyVFBeasur ed at FB,I N = 2V to 26V ,
SKIP = VDDVREFIN = 2.0V1.9852.015
REFERENCEReference VoltageVREFVCC = 4.5V to 5.5V1.9852.015V
FAULT DETECTIONOutput Overvoltage-Protection
Trip ThresholdOVP
With respect to the internal target voltage
(error comparator threshold); rising edge;
hysteresis = 50mV
250350mV
Output Undervoltage-Protection
Trip ThresholdUVP
With respect to the internal target voltage
(error comparator threshold);
falling edge; hysteresis = 50mV
-240-160mV
Output Undervoltage
Fault-Propagation DelaytUVPFB forced 25mV below trip threshold80400μs
PGOOD Output Low VoltageISINK = 3mA0.4V
VCC Undervoltage Lockout
ThresholdV U V L O( V C C ) Ri si ng ed g e, P W M d i sab l ed b el ow thi s l evel ;
hysteresis = 100mV3.954.45V
CURRENT LIMITILIM Input Range0.4VREFV
VILIM = 0.4V1723Current-Limit ThresholdVILIMITILIM = REF (2.0V)90110mV
Ultrasonic FrequencySKIP = open (3.3V); VFB = VREFIN + 50mV17kHz
GATE DRIVERSLow state (pulldown)3.5DH Gate Driver On-ResistanceRON(DH)BST - LX forced
to 5VHigh state (pullup)3.5Ω
High state (pullup)4DL Gate Driver On-ResistanceRON(DL)Low state (pulldown)2Ω
Inter nal BS T S w i tch On- Resi stanceRBSTIBST = 10mA, VDD = 5V7Ω
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
Note 1:Limits are 100% production tested at TA = +25°C. Maximum and minimum limits over temperature are guaranteed by
design and characterization.
Note 2:The 0 to 0.5V range is guaranteed by design, not production tested.
Note 3:On-time and off-time specifications are measured from 50% point to 50% point at the DH pin with LX = GND, VBST= 5V,
and a 250pF capacitor connected from DH to LX. Actual in-circuit times can differ due to MOSFET switching speeds.
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Figure 1, VIN= 12V, VDD= VCC= VEN= 5V, REFIN = ILIM = REF, SKIP= GND. TA= -40°C to +85°C, unless otherwise
specified.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
INPUTS AND OUTPUTSEN Logic-Input ThresholdVENEN rising edge; hysteresis = 450mV (typ)1.202.20V
High (5V VDD)VCC -
Mid (3.3V)3.03.6
Ref (2.0V)1.72.3
SKIP Quad-Level Input Logic
LevelsVSKIP
Low (GND)0.4
1.5V OUTPUT EFFICIENCY
vs. LOAD CURRENTMAX8792 toc01
LOAD CURRENT (A)
EFFICIENCY (%)0.1
20V
SKIP MODE
PWM MODE
12V
1.5V OUTPUT EFFICIENCY
vs. LOAD CURRENTMAX8792 toc02
LOAD CURRENT (A)
EFFICIENCY (%)0.1
SKIP MODE
PWM MODE
LOW-NOISE
MODE
1.5V OUTPUT VOLTAGE
vs. LOAD CURRENTMAX8792 toc03
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)82
SKIP MODE
PWM MODE
LOW-NOISE
MODE
Typical Operating Characteristics(MAX8792 Circuit of Figure 1, VIN = 12V, VDD= 5V, SKIP= GND, RTON= 200kΩ, TA = +25°C, unless otherwise noted.)
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
1.05V OUTPUT EFFICIENCY
vs. LOAD CURRENTMAX8792 toc04
LOAD CURRENT (A)
EFFICIENCY (%)0.1
20V
SKIP MODE
PWM MODE
12V
1.05V OUTPUT EFFICIENCY
vs. LOAD CURRENTMAX8792 toc05
LOAD CURRENT (A)
EFFICIENCY (%)0.1
SKIP MODE
PWM MODE
LOW-NOISE
MODE
1.05V OUTPUT VOLTAGE
vs. LOAD CURRENTMAX8792 toc06
LOAD CURRENT (A)
OUTPUT VOLTAGE (V)82
SKIP MODE
PWM MODE
LOW-NOISE
MODE
SWITCHING FREQUENCY
vs. LOAD CURRENTMAX8792 toc07
LOAD CURRENT (A)
SWITCHING FREQUENCY (kHz)0.1
SKIP MODE
LOW-NOISE
MODE
PWM MODE
PWM MODE SWITCHING FREQUENCY
vs. INPUT VOLTAGEMAX8792 toc08
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (kHz)1810
ILOAD = 5A
NO LOAD
SWITCHING FREQUENCY
vs. TEMPERATUREMAX8792 toc09
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)406080-200
ILOAD = 10A
ILOAD = 5A
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGEMAX8792 toc10
INPUT VOLTAGE (V)
MAXIMUM OUTPUT CURRENT (A)1821912
MAXIMUM OUTPUT CURRENT
vs. TEMPERATURE
MAX8792 toc11
TEMPERATURE (°C)
MAXIMUM OUTPUT CURRENT (A)406080100-200
WITHOUT TEMPERATURE
COMPENSATION
R4 = R5 = 49.9kΩ
WITH
TEMPERATURE
COMPENSATION
(FIGURE 1)
NO-LOAD SUPPLY CURRENT IBIAS
vs. INPUT VOLTAGEMAX8792 toc12
INPUT VOLTAGE (V)
IBIAS
(mA)1518219
SKIP MODE
PWM MODE
LOW-NOISE MODE
Typical Operating Characteristics (continued)(MAX8792 Circuit of Figure 1, VIN = 12V, VDD= 5V, SKIP= GND, RTON= 200kΩ, TA = +25°C, unless otherwise noted.)
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
NO-LOAD SUPPLY CURRENT IIN
vs. INPUT VOLTAGEMAX8792 toc13
INPUT VOLTAGE (V)
(mA)1518219
SKIP MODE
PWM MODE
LOW-NOISE MODE
REF OUTPUT VOLTAGE
vs. LOAD CURRENTMAX8792 toc14
LOAD CURRENT (μA)
OUTPUT VOLTAGE (V)50709010010204060800
REFIN-TO-FB OFFSET
VOLTAGE DISTRIBUTION
MAX8792 toc15
OFFSET VOLTAGE (mV)
SAMPLE PERCENTAGE (%)
+85°C
+25°C
SAMPLE SIZE = 100
20V ILIM THRESHOLD
VOLTAGE DISTRIBUTION
MAX8792 toc16
ILIM THRESHOLD VOLTAGE (mV)
SAMPLE PERCENTAGE (%)
+85°C
+25°C
SAMPLE SIZE = 100
SOFT-START WAVEFORM
(HEAVY LOAD)MAX8792 toc17
200μs/div
C. VOUT, 1V/div
B. INDUCTOR CURRENT,
10A/div
1.5VA
A. EN, 5V/div
B. PGOOD, 5V/div
SOFT-START WAVEFORM
(LIGHT LOAD)MAX8792 toc18
200μs/div
C. VOUT, 1V/div
B. INDUCTOR CURRENT,
10A/div
1.5VA
A. EN, 5V/div
B. PGOOD, 5V/div
SHUTDOWN WAVEFORMMAX8792 toc19
200μs/div
D. VOUT, 1V/div
E. INDUCTOR CURRENT,
1.5V
A. EN, 5V/div
B. PGOOD, 5V/div
LOAD-TRANSIENT RESPONSE
(PWM MODE)MAX8792 toc20
20μs/div
C. INDUCTOR CURRENT,
10A/div
1.45V
1.55V
A. IOUT = 1A TO 8A, 10A/div
B. VOUT, 50mV/div
LOAD-TRANSIENT RESPONSE
(SKIP MODE)MAX8792 toc21
20μs/div
C. INDUCTOR CURRENT,
10A/div
1.45V
1.55V
10A
A. IOUT = 1A TO 8A, 10A/div
B. VOUT, 50mV/div
Typical Operating Characteristics (continued)(MAX8792 Circuit of Figure 1, VIN = 12V, VDD= 5V, SKIP= GND, RTON= 200kΩ, TA = +25°C, unless otherwise noted.)
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
OUTPUT OVERLOAD WAVEFORM
(UVP ENABLED)MAX8792 toc22
200μs/div
C. DL, 5V/div
D. PGOOD, 5V/div
14A
1.5V
A. INDUCTOR CURRENT,
10A/div
B. VOUT, 1V/div
OUTPUT OVERVOLTAGE WAVEFORMMAX8792 toc23
100μs/div
C. PGOOD, 5V/div
1.5V
A. VOUT, 1V/div
B. DL, 5V/div
DYNAMIC OUTPUT-VOLTAGE TRANSITION
(PWM MODE)MAX8792 toc24
20μs/div
C. INDUCTOR CURRENT,
10A/div
D. LX, 10V/div
-10A
1.5V
1.5V
1.05V
1.05V
12V
A. REFIN, 500mV/div
B. VOUT, 200mV/div
DYNAMIC OUTPUT-VOLTAGE TRANSITION
(SKIP MODE)MAX8792 toc25
100μs/div
C. INDUCTOR CURRENT,
10A/div
D. LX, 10V/div
10A
1.5V
1.5V
1.05V
1.05V
12V
A. REFIN, 500mV/div
B. VOUT, 200mV/div
Typical Operating Characteristics (continued)(MAX8792 Circuit of Figure 1, VIN = 12V, VDD= 5V, SKIP= GND, RTON= 200kΩ, TA = +25°C, unless otherwise noted.)
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
Pin Description
PINNAMEFUNCTION1EN
Shutdown Control Input. Connect to VDD for normal operation. Pull EN low to place the controller into
its 2μA shutdown state. When disabled, the MAX8792 slowly ramps down the target/output voltage to
ground and after the target voltage reaches 0.1V, the controller forces both DH and DL low and
enters the low-power shutdown state. Toggle EN to clear the fault-protection latch.
2VDDSupply Voltage Input for the DL Gate Driver. Connect to the system supply voltage (+4.5V to +5.5V).
Bypass VDD to power ground with a 1μF or greater ceramic capacitor.
3DL Low-Side Gate Driver. DL swings from GND to VDD. The controller pulls DL high when an output
overvoltage fault is detected, overriding any negative current-limit condition that may be present. The
MAX8792 forces DL low during VCC UVLO and REFOK lockout conditions.LXInductor Connection. Connect LX to the switched side of the inductor as shown in Figure 1.
5DH High-Side Gate Driver. DH swings from LX to BST. The MAX8792 pulls DH low whenever the
controller is disabled.BSTBoost Flying-Capacitor Connection. Connect to an external 0.1μF 6V capacitor as shown in Figure 1.
The MAX8792 contains an internal boost switch/diode (see Figure 2).
7TON
Switching Frequency-Setting Input. An external resistor between the input power source and TON
sets the switching period (TSW = 1/fSW) according to the following equation:
where CTON = 16.26pF and VFB = VREFIN under normal operating conditions. If the TON current
drops below 10μA, the MAX8792 shuts down, and enters a high-impedance state.
TON is high impedance in shutdown.
8FB
Feed b ack V ol tag e- S ense C onnecti on. C onnect d i r ectl y to the p osi ti ve ter m i nal of the outp ut cap aci tor s
for outp ut vol tag es l ess than 2V as show n i n Fi g ur e 1. For fi xed - outp ut vol tag es g r eater than 2V ,
connect RE FIN to RE F and use a r esi sti ve d i vi d er to set the outp ut vol tag e ( Fi g ur e 4) . FB senses the
outp ut vol tag e to d eter m i ne the on- ti m e for the hi g h- si d e sw i tchi ng M OS FE T.ILIM
Current-Limit Threshold Adjustment. The current-limit threshold is 0.05 times (1/20) the voltage at
ILIM. Connect ILIM to a resistive divider (from REF) to set the current-limit threshold between 20mV
and 100mV (with 0.4V to 2V at ILIM).REFIN
External Reference Input. REFIN sets the feedback regulation voltage (VFB = VREFIN) of the MAX8792
using the resistor-divider connected between REF and GND. The MAX8792 includes an internal
window comparator to detect REFIN voltage transitions, allowing the controller to blank PGOOD and
the fault protection.REF2V Reference Voltage. Bypass to analog ground using a 470pF to 10nF ceramic capacitor. The
reference can source up to 50μA for external loads.SKIP
Pulse-Skipping Control Input. This four-level input determines the mode of operation under normal
steady-state conditions and dynamic output-voltage transitions:
VDD (5V) = forced-PWM operation.
REF (2V) = pulse-skipping mode with forced-PWM during transitions.
Open (3.3V)= ultrasonic mode (without forced-PWM during transitions).
GND = pulse-skipping mode (without forced-PWM during transitions).VCC5V Analog Supply Voltage. Internally connected to VDD through an internal 20Ω resistor. Bypass VCC
to analog ground using a 1μF ceramic capacitor.RkVSWTONTONFB
OUT=+()⎛⎜⎞⎟65.Ω
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
Standard Application CircuitsThe MAX8792 standard application circuit (Figure 1) gen-
erates a 1.5V or 1.05V output rail for general-purpose use
in a notebook computer. See Table 1 for component
selections. Table 2 lists the component manufacturers.
Pin Description (continued)
PINNAMEFUNCTIONPGOOD
Open-Drain Power-Good Output. PGOOD is low when the output voltage is more than 200mV (typ)
below or 300mV (typ) above the target voltage (VREFIN), during soft-start and soft-shutdown. After the
soft-start circuit has terminated, PGOOD becomes high impedance if the output is in regulation.
PGOOD is blanked—forced high-impedance state—when a dynamic REFIN transition is detected.
(15)GNDGround/Exposed Pad. Internally connected to the controller’s ground plane and substrate.
Connect directly to ground.1μFOFFON
VDD
VCC
1μF
PGOOD
R10
100kΩ
REFIN
54.9kΩ
BST
CBST
0.1μF
COUT
TON
97.6kΩ
GND/OPEN/REF/VDDLO
REF
ILIM
NTC
100kΩ
B = 4250
REF
RTON
200kΩ
82kΩ
68kΩ
AGND
AGND
PWR
PWR
PWR
AGND
AGNDPWR
AGND
AGND
GND (EP)
SKIP
OUTPUT
1.05V/1.50V
10A (MAX)
INPUT
7V TO 24V
5V BIAS
SUPPLY
MAX8792
CIN
PWR
1000pF
49.9kΩ
Figure 1. MAX8792 Standard Application Circuit
SEE TABLE 1 FOR COMPONENT SELECTION.
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
Detailed DescriptionThe MAX8792 step-down controller is ideal for the low-
duty-cycle (high-input voltage to low-output voltage)
applications required by notebook computers. Maxim’s
proprietary Quick-PWM pulse-width modulator in the
MAX8792 is specifically designed for handling fast load
steps while maintaining a relatively constant operating
frequency and inductor operating point over a wide
range of input voltages. The Quick-PWM architecture
circumvents the poor load-transient timing problems of
fixed-frequency, current-mode PWMs while also avoid-
ing the problems caused by widely varying switching
frequencies in conventional constant-on-time (regard-
less of input voltage) PFM control schemes.
+5V Bias Supply (VCC/VDD)The MAX8792 requires an external 5V bias supply in
addition to the battery. Typically, this 5V bias supply is
the notebook’s main 95% efficient 5V system supply.
Keeping the bias supply external to the IC improves
efficiency and eliminates the cost associated with the
5V linear regulator that would otherwise be needed to
supply the PWM circuit and gate drivers. If stand-alone
capability is needed, the 5V supply can be generated
with an external linear regulator such as the MAX1615.
The 5V bias supply powers both the PWM controller
and internal gate-drive power, so the maximum current
drawn is determined by:
IBIAS= IQ+ fSWQG= 2mA to 20mA (typ)
Table 1. Component Selection for Standard Applications
VOUT = 1.5V/1.05V AT 10A
(Figure 1)
VOUT = 3.3V AT 5A
(Figure 4)
VOUT = 1.5V AT 10A/1.05V AT
7A (Figure 7)COMPONENTVIN = 7V to 20V
RTON = 200kΩ (300kHz)
VIN = 7V to 20V
RTON = 332kΩ (300kHz)
VIN = 4V to 12V
RTON = 100kΩ (600kHz)
Input Capacitor(2x) 10μF, 25V
Taiyo Yuden TMK432BJ106KM
(2x) 10μF, 25V
Taiyo Yuden TMK432BJ106KM
(2x) 10μF, 25V
Taiyo Yuden TMK432BJ106KM
Output Capacitor(2x) 330μF, 6mΩ
Panasonic EEFSX0D331XR
(1x) 330μF, 18mΩ
SANYO 4TPE330MI
(2x) 330μF, 7mΩ
NEC-TOKIN PSGD0E337M7
Inductor1.0μH, 3.25mΩ
Würth 744 3552 100
3.3μH, 14mΩ
NEC-TOKIN MPLC1040L3R3
0.68μH, 4.6mΩ
Coiltronics FP3-R68
High-Side MOSFETFairchild (1x) FDS8690
8.6mΩ/11.4mΩ (typ/max)
Fairchild (1x) FDS8690
8.6mΩ/11.4mΩ (typ/max)
Low-Side MOSFETFairchild (1x) FDS8670
4.2mΩ/5.0mΩ (typ/max)
Siliconix (1x) Si4916DY
NH = 18mΩ/22mΩ (typ/max)
NL = 15mΩ/18mΩ (typ/max)Fairchild (1x) FDS8670
4.2mΩ/5.0mΩ (typ/max)
Table 2. Component Suppliers
MANUFACTURERWEBSITEAVX Corp.www.avxcorp.com
BI Technologieswww.bitechnologies.com
Central
Semiconductor Corp.www.centralsemi.com
Coiltronicswww.cooperet.com
Fairchild
Semiconductorwww.fairchildsemi.com
International Rectifierwww.irf.com
KEMET Corp.www.kemet.com
NEC TOKIN America,
Inc.www.nec-tokin.com
Panasonic Corp.www.panasonic.com
MANUFACTURERWEBSITEPulse Engineeringwww.pulseeng.com
Renesas Technology
Corp.www.renesas.com
SANYO Electric Co.,
Ltd.www.sanyo.com
Siliconix (Vishay)www.vishay.com
Sumida Corp.www.sumida.com
Taiyo Yudenwww.t-yuden.com
TDK Corp.www.component.tdk.com
TOKO America, Inc.www.tokoam.com
Würth Electronik
GmbH & Co. KGwww.we-online.com
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
Free-Running Constant-On-Time PWM
Controller with Input Feed-ForwardThe Quick-PWM control architecture is a pseudo-fixed-
frequency, constant on-time, current-mode regulator
with voltage feed-forward (Figure 2). This architecture
relies on the output filter capacitor’s ESR to act as a cur-
rent-sense resistor, so the output ripple voltage provides
the PWM ramp signal. The control algorithm is simple:
the high-side switch on-time is determined solely by a
one-shot whose pulse width is inversely proportionalto
DYNAMIC OUTPUT
TRANSITION DETECTION
BST
ONE-SHOT
TRIGQ
tOFF(MIN)ON-TIME
COMPUTE
TON
ERROR
AMPLIFIER
EA + 0.3V
ONE-SHOT
TRIGQ
tON
ZERO CROSSINGPGOOD
PGOOD
AND FAULT
PROTECTION
SKIP
EA - 0.2V
BLANK
REFIN
VALLEY CURRENT LIMIT
GNDDH
SOFT-
START/STOP
QUAD-
LEVEL
DECODEBLANK
VCC
VDD
REF
AUL
INTEGRATOR
(CCV)
REF
ILIM
MAX8792
MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFINinput voltage and directly proportional to output volt-
age. Another one-shot sets a minimum off-time (200ns
typ). The on-time one-shot is triggered if the error com-
parator is low, the low-side switch current is below the
valley current-limit threshold, and the minimum off-time
one-shot has timed out.
On-Time One-ShotThe heart of the PWM core is the one-shot that sets the
high-side switch on-time. This fast, low-jitter, adjustable
one-shot includes circuitry that varies the on-time in
response to input and output voltage. The high-side
switch on-time is inversely proportional to the input volt-
age as sensed by the TON input, and proportional to
the feedback voltage as sensed by the FB input:
On-Time (tON) = TSW(VFB/VIN)
where TSW(switching period) is set by the resistance
(RTON) between TON and VIN. This algorithm results in
a nearly constant switching frequency despite the lack
of a fixed-frequency clock generator. Connect a resis-
tor (RTON) between TON and VINto set the switching
period TSW= 1/fSW:
where CTON= 16.26pF. When used with unity-gain feed-
back (VOUT= VFB), a 96.75kΩto 303.25kΩcorresponds
to switching periods of 167ns (600kHz) to 500ns
(200kHz), respectively. High-frequency (600kHz) opera-
tion optimizes the application for the smallest compo-
nent size, trading off efficiency due to higher switching
losses. This may be acceptable in ultra-portable devices
where the load currents are lower and the controller is
powered from a lower voltage supply. Low-frequency
(200kHz) operation offers the best overall efficiency at
the expense of component size and board space.
For continuous conduction operation, the actual switching
frequency can be estimated by:
where VDISis the sum of the parasitic voltage drops in
the inductor discharge path, including synchronous recti-
fier, inductor, and PCB resistances; VCHGis the sum of
the parasitic voltage drops in the charging path, includ-
ing the high-side switch, inductor, and PCB resistances;
and tONis the on-time calculated by the MAX8792.
Power-Up Sequence (POR, UVLO)The MAX8792 is enabled when EN is driven high and
the 5V bias supply (VDD) is present. The reference
powers up first. Once the reference exceeds its UVLO
threshold, the internal analog blocks are turned on and
masked by a 50μs one-shot delay in order to allow the
bias circuitry and analog blocks enough time to settle
to their proper states. With the control circuitry reliably
powered up, the PWM controller may begin switching.
Power-on reset (POR) occurs when VCCrises above
approximately 3V, resetting the fault latch and prepar-
ing the controller for operation. The VCCUVLO circuitry
inhibits switching until VCCrises above 4.25V. The con-
troller powers up the reference once the system
enables the controller, VCCexceeds 4.25V, and EN is
driven high. With the reference in regulation, the con-
troller ramps the output voltage to the target REFIN volt-
age with a 1mV/μs slew rate:
The soft-start circuitry does not use a variable current
limit, so full output current is available immediately.
PGOOD becomes high impedance approximately
200μs after the target REFIN voltage has been reached.
The MAX8792 automatically uses pulse-skipping mode
during soft-start and uses forced-PWM mode during
soft-shutdown, regardless of the SKIPconfiguration.
For automatic startup, the battery voltage should be
present before VCC. If the controller attempts to bring
the output into regulation without the battery voltage
present, the fault latch trips. The controller remains shut
down until the fault latch is cleared by toggling EN or
cycling the VCCpower supply below 0.5V.
If the VCCvoltage drops below 4.25V, the controller
assumes that there is not enough supply voltage to
make valid decisions. To protect the output from over-
voltage faults, the controller shuts down immediately
and forces a high-impedance output (DL and DH
pulled low).
ShutdownWhen the system pulls EN low, the MAX8792 enters
low-power shutdown mode. PGOOD is pulled low
immediately, and the output voltage ramps down with a
1mV/μs slew rate:Vs
VmsSHDNFBFB==11μVs
VmsSTARTFBFB==11μVVVVSW
OUTDISINDISCHG=+()−()RkVSWTONTONFB
OUT=+⎛⎜⎞⎟(.)65Ω
