MAX1761EEE+ ,Small, Dual, High-Efficiency Buck Controller for Notebooksapplications, such as♦ Flexible Output Voltagesnotebook computers and smart phones. OUT1: Dual Mode ..
MAX1762EUB ,High-Efficiency, 10-Pin レMAX, Step-Down Controllers for NotebooksApplications PART TEMP. RANGE PIN-PACKAGE Notebooks Handy-TerminalsMAX1762EUB -40°C to +85°C 10 µMA ..
MAX1762EUB ,High-Efficiency, 10-Pin レMAX, Step-Down Controllers for NotebooksMAX1762/MAX179119-1923; Rev 0; 1/01High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks
MAX1762EUB ,High-Efficiency, 10-Pin レMAX, Step-Down Controllers for Notebooksapplications such as subnotebook 0.5V to 5.5V Output Adjust Rangecomputers and smart phones. PWM o ..
MAX1762EUB+ ,High-Efficiency, 10-Pin µMAX, Step-Down Controllers for NotebooksELECTRICAL CHARACTERISTICS(V = 15V, VL enabled, C = 1µF, C = 0.1µF, T = 0 to +85°C, unless otherwis ..
MAX1763EEE ,1.5A, Low-Noise, 1MHz, Step-Up DC-DC ConverterELECTRICAL CHARACTERISTICS(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, V = V = V = 3.6 ..
MAX4586EUB+T ,Serially Controlled, 4-Channel Audio/Video MultiplexersELECTRICAL CHARACTERISTICS—Single +5V Supply(V+ = +5V ±5%, T = T to T , unless otherwise noted. Typ ..
MAX4588 ,Low-Voltage, High-Isolation, Dual 4-Channel RF Video MultiplexerApplicationsInterfaceRF Switching Automatic Test Equipment♦ >±2kV ESD Protection per Method 3015.7V ..
MAX4588CAI ,Low-Voltage, High-Isolation, Dual 4-Channel RF/Video MultiplexerELECTRICAL CHARACTERISTICS—Dual Supplies(V+ = V = +4.5V to +5.5V, V- = -4.5V to -5.5V, V = +2.4V, V ..
MAX4588CWI+ ,Low-Voltage, High-Isolation, Dual 4-Channel RF Video MultiplexerApplicationsInterfaceRF Switching Automatic Test Equipment♦ >±2kV ESD Protection per Method 3015.7V ..
MAX4588EAI ,Low-Voltage, High-Isolation, Dual 4-Channel RF/Video MultiplexerFeaturesThe MAX4588 low-voltage, dual 4-channel multiplexer' Low Insertion Loss: -2.5dB up to 100MH ..
MAX458CPL ,8x4 Video Crosspoint Switches with BuffersFeatures' 100MHz Unity-Gain BandwidthThe MAX458/MAX459 are crosspoint switches with eight' 300V/µs ..
MAX1761EEE+
Small, Dual, High-Efficiency Buck Controller for Notebooks
General DescriptionThe MAX1761 dual pulse-width-modulation (PWM),
step-down controller provides high efficiency, excellent
transient response, and high DC output accuracy in an
extremely compact circuit topology. These features are
essential for stepping down high-voltage batteries to
generate low-voltage CPU core, I/O, and chipset RAM
supplies in PC board area critical applications, such as
notebook computers and smart phones.
Maxim’s proprietary Quick-PWM™ quick-response,
constant-on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides
“instant-on” response to load transients while maintain-
ing a relatively constant switching frequency.
The MAX1761 achieves high efficiency at reduced cost
by eliminating the current-sense resistor found in tradi-
tional current-mode PWMs. Efficiency is further
enhanced by its ability to drive large synchronous-recti-
fier MOSFETs. The MAX1761 employs a complemen-
tary MOSFET output stage, which reduces component
count by eliminating external bootstrap capacitors and
diodes.
Single-stage buck conversion allows this device to
directly step down high-voltage batteries for the highest
possible efficiency. Alternatively, two-stage conversion
(stepping down the +5V system supply instead of the
battery) at a higher switching frequency allows the mini-
mum possible physical size.
The MAX1761 is intended for CPU core, chipset,
DRAM, or other low-voltage supplies. The MAX1761 is
available in a 16-pin QSOP package. For applications
requiring greater output power, refer to the MAX1715
data sheet. For a single-output version, refer to the
MAX1762/MAX1791 data sheet.
________________________ApplicationsNotebooks and PDAs
Digital Cameras
Handy-Terminals
Smart Phones
1.8V/2.5V Logic and I/O Supplies
FeaturesFree-Running On-Demand PWMSelectable Light-Load Pulse-Skipping Operation ±1% Total DC Error in Forced-PWM Mode5V to 20V Input RangeFlexible Output Voltages
OUT1: Dual Mode™Fixed 2.5V or 1V to 5.5V
Adjustable
OUT2: Dual Mode Fixed 1.8V or 1V to 5.5V
AdjustableOutput Undervoltage Protection Complementary Synchronous BuckNo Current-Sense Resistor4.65V at 25mA Linear Regulator Output 4µA V+ Shutdown Supply Current5µA VL Shutdown Supply Current950µA Quiescent Supply CurrentTiny 16-Pin QSOP Package
MAX1761
Small, Dual, High-Efficiency
Buck Controller for NotebooksFB1DH1
CS1
DL1
GND
DL2
CS2
DH2
TOP VIEW
MAX1761
QSOPOUT1
REF
ON1
ON2
OUT2
FB2
Pin Configuration19-1835; Rev 0; 10/00
EVALUATION KIT
AVAILABLE
Ordering Information16 QSOP
PIN-PACKAGETEMP. RANGE-40°C to +85°CMAX1761EEE
PARTQuick-PWM and Dual Mode are trademarks of
Maxim Integrated Products.
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(Circuit of Figure 1, V+ = 15V, CVL= 4.7µF, CREF= 0.1µF, VL not externally driven unless otherwise noted, TA
= 0°C to +85°C, unlessotherwise noted.) (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.
V+ to GND..............................................................-0.3V to +22V
VL to GND................................................................-0.3V to +6V
VL to V+ .............................................................................+0.3V
OUT_, ON2 to GND..................................................-0.3V to +6V
ON1, DH_ to GND........................................-0.3V to (V+ + 0.3V)
FB_, REF, DL_ to GND.................................-0.3V to (VL + 0.3V)
CS_ to GND.....................................................-2V to (V+ + 0.3V)
REF Short Circuit to GND...........................................Continuous
Continuous Power Dissipation
16-Pin QSOP (derate 8.3mW/°C above +70°C)......….667mW
Operating Temperature Range...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature.........................................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
PWM CONTROLLERSInput Voltage RangeV+(Note 2)4.520V
FB_ = OUT_0.9911.01
FB1 = GND2.4752.52.525VDC Output Voltage Accuracy
(Note 3)VOUT_
V+ = 4.5V to 20V,
VL = 4.75V to 5.25V,
ON2 = VLFB2 = GND1.7821.81.818
Output Voltage Adjust Range15.5V
OUT_ Input Resistance80160300kΩ
FB_ Input Bias CurrentVFB_ = 1V, VL = 5V-0.10.1µA
CS_ Input Bias CurrentVCS_ = 0, VL = 5V-11µA
Soft-Start Ramp TimeZero to full ILIM1700µs
OUT1661735809On-Time (Note 4)tONV+ = 10V, VOUT1 = 2.5V,
VOUT2 = 1.8VOUT2648720792ns
Minimum Off-Time (Note 4)tOFF400500ns
BIAS AND REFERENCEFB1 = FB2 = GND, VL = 5V, VOUT1 and
VOUT2 forced above regulation point0.601.20mA
VL undriven0.951.70Quiescent Supply Current
FB1 = FB2 = GND, VOUT1
and VOUT2 forced
above regulation pointVL = 5V0.380.65VL = 5V, ON1 = ON2 = GND510µAShutdown Supply CurrentI+VL = 0, 5V410µA
VL Output VoltageVLILOAD = 0 to 25mA, V+ = 5V to 20V4.54.654.75V
Reference VoltageVREFV+ = 5V to 20V, no load1.9822.02V
Reference Load RegulationIREFIREF = 0 to 50µA8mV
REF Sink CurrentREF in regulation10µA
Falling edge1.6REF Fault Lockout VoltageRising edge1.94V
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
FAULT PROTECTIONOutput Undervoltage Threshold
(Foldback)VFB,UVFBWith respect to the regulation point, no load607080%
Output Undervoltage Blanking
TimeVFB,UVLO(t)Measured from ON_ signal going high1032ms
GND - CS_, positive direction92100108
GND - CS_, negative direction, ON2 = floating-135-120-105Current-Limit Threshold
GND - CS_, zero crossing, ON2 = 5V2.5
Thermal Shutdown ThresholdHysteresis = 10oC160oC
VL Undervoltage Lockout
ThresholdVVL,UVLORising edge, hysteresis = 20mV, PWM is
disabled below this voltage4.14.4V
GATE DRIVERSDH_ Gate Driver On-Resistance
(Pullup)V+ = 6V to 20V, DH_, high state3.78Ω
DH_ Gate Driver On-Resistance
(Pulldown)DH_, low state6.210Ω
DL_ Gate Driver On-Resistance
(Pullup)DL_ , high state3.48Ω
DL_ Gate Driver On-Resistance
(Pulldown)DL_, low state2.05Ω
DH_ Gate Driver Source/Sink
CurrentVDH_ = 3V, V+ = 6V0.6A
DL_ Gate Drive Sink CurrentVDL_ = 2.5V0.9A
DL_ Gate Drive Source CurrentVDL_ = 2.5V0.5A
LOGIC CONTROLSON_ Logic Input High Voltage2.05V
ON2 Logic Input Float Voltage
(Forced-PWM Mode)2.0V < VON1 < VL1.31.71.95V
ON_ Logic Input Low Voltage0.5V
ON1 Logic Input Current-11µA
ON2 Logic High Input CurrentVON2 > 2.0V013µA
ON2 Logic Low Input CurrentVON2 < 0.5V, VON1 > 2.0V-2-10µA
FB_ Dual Mode Threshold50100150mV
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Figure 1, V+ = 15V, CVL= 4.7µF, CREF= 0.1µF, VL not externally driven unless otherwise noted, TA
= 0°C to +85°C, unlessotherwise noted.) (Note 1)
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
PWM CONTROLLERS(Note 2)4.520VInput Voltage RangeVLVL externally driven (Note 2)4.755.25
FB_ = OUT_0.991.01
FB1 = GND2.4752.525VDC Output Voltage Accuracy
(Note 3)VOUT_
V+ = 4.5V to 20V,
VL = 4.75V to 5.25V,
ON2 = VLFB2 = GND1.7821.818
Output Voltage Adjust Range15.5V
OUT_ Input Resistance80300kΩ
FB_ Input Bias CurrentVFB_ = 1V, VL = 5V-0.10.1µA
CS_ Input Bias CurrentVCS_ = 0, VL = 5V-11µA
Soft-Start Ramp TimeZero to full ILIMµs
OUT1661809On-Time (Note 4)tONV+ = 10V, VOUT1 = 2.5V,
VOUT2 = 1.8VOUT2648792ns
Minimum Off-Time (Note 4)tOFFAbove regulation point500ns
BIAS AND REFERENCEFB1 = FB2 = GND, VL = 5V, VOUT1 and
VOUT2 forced above regulation point1.2mA
VL undriven1.7Quiescent Supply Current
FB1 = FB2 = GND, VOUT1
and VOUT2 forced above
regulation pointVL = 5V0.5VL = 5V, ON1 = ON2 = GND10µAShutdown Supply CurrentI+VL = 0, 5V10µA
VL Output VoltageVLILOAD = 0 to 25mA, V+ = 5V to 20V4.54.75V
Reference VoltageVREFV+ = 5V to 20V, no load1.982.02V
Reference Load RegulationIREFIREF = 0 to 50µA8mV
REF Sink CurrentREF in regulation10µA
FAULT PROTECTIONOutput Undervoltage Threshold
(Foldback)VFB,UVFBWith respect to the regulation point, no load6080%
Output Undervoltage Lockout
TimerVFB,UVLO(t)Measured from ON_ signal going high1032ms
GND – CS_, positive direction92108Current-Limit ThresholdGND – CS_, negative direction, ON2 = floating-135-105mV
VL Undervoltage Lockout
ThresholdVVL,UVLORising edge, hysteresis = 20mV, PWM is
disabled below this voltage4.14.4V
ELECTRICAL CHARACTERISTICS(Circuit of Figure 1, V+ = 15V, CVL= 4.7µF, CREF= 0.1µF, VL not externally driven unless otherwise noted, TA
= -40°C to +85°C,unless otherwise noted.) (Note 1)
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GATE DRIVERSDH_ Gate Driver On-Resistance
(Pullup)V+ = 6V to 20V, DH_, high state8Ω
DH_ Gate Driver On-Resistance
(Pulldown)DH_, low state10Ω
DL_ Gate Driver On-Resistance
(Pullup)DL_, high state8Ω
DL_ Gate Driver On-Resistance
(Pulldown)DL_, low state5Ω
DH_ Gate Driver Source/Sink
CurrentVDH_ = 3V, V+ = 6VA
DL_ Gate Drive Sink CurrentVDL_ = 2.5VA
DL_ Gate Driver Source CurrentVDL_ = 2.5VA
LOGIC CONTROLSON_ Logic Input High Voltage2.05V
ON2 Logic Input Float Voltage
(Forced-PWM Mode)VON1 > 2.0V1.31.95V
ON_ Logic Input Low Voltage0.5V
ON1 Logic Input Current-11µA
ON2 Logic High Input CurrentVON2 > 2.0V03µA
ON2 Logic Low Input CurrentVON2 < 0.5V, VON1 > 2.0V-20µA
FB_ Dual Mode Threshold50150mV
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Figure 1, V+ = 15V, CVL= 4.7µF, CREF= 0.1µF, VL not externally driven unless otherwise noted, TA
= -40°C to +85°C,unless otherwise noted.) (Note 1)
Note 1:Specifications to -40°C are guaranteed by design, not production tested.
Note 2:If V+ is less than 5V, V+ must be connected to VL. If VL is connected to V+, V+ must be between 4.5V and 5.5V.
Note 3:DC output accuracy specifications refer to the trip-level error of the error amplifier. The output voltage will have a DC regula-
tion higher than the trip level by 50% of the ripple. In PFM mode, the output will rise by approximately 1.5% when transition-
ing from continuous conduction to no load.
Note 4:One-shot times are measured at the DH pin (V+ = 15V, CDH= 400pF, 90% point to 90% point). Actual in-circuit times may
be different due to MOSFET switching speeds.This effect can also cause the switching frequency to vary.
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
10010100100010,000
EFFICIENCY vs. LOAD CURRENT
(VOUT = 2.5V, SKIP MODE)MAX1761 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)40V+ = +5V = VL
V+ = +18V
V+ = +7V
V+ = +12V
10010100100010,000
EFFICIENCY vs. LOAD CURRENT
(3.3V, SKIP MODE)MAX1761 toc05
LOAD CURRENT (mA)
EFFICIENCY (%)40
V+ = +5V = VL
V+ = +7V
V+ = +12V
V+ = +18V
10010100100010,000
EFFICIENCY vs. LOAD CURRENT
(3.3V, PWM MODE)MAX1761 toc06
LOAD CURRENT (mA)
EFFICIENCY (%)40V+ = +5V = VL
V+ = +7V
V+ = +12V
V+ = +18V
FREQUENCY vs. LOAD CURRENT
MAX1761 toc08
LOAD CURRENT (mA)
FREQUENCY (kHz)
SKIP MODE
PWN MODE
VOUT = + 2.5V
VOUT = + 1.8V
VOUT = + 2.5V
VOUT = + 1.8V
VL VOLTAGE vs. OUTPUT CURRENT
MAX1761 toc09
VL CURRENT (mA)
VL ERROR (%)
VOUT1 = 2.5V, IOUT1 = 2A,
VOUT2 = 1.8V, IOUT2 = 2A
10010100100010,000
EFFICIENCY vs. LOAD CURRENT
(1.8V, PWM MODE)MAX1761 toc04
LOAD CURRENT (mA)
EFFICIENCY (%)40
V+ = +5V = VL
V+ = +7V
V+ = +12V
V+ = +18V
10010100100010,000
EFFICIENCY vs. LOAD CURRENT
(2.5V, SKIP MODE, 3.5A COMPONENTS)MAX1761 toc07
LOAD CURRENT (mA)
EFFICIENCY (%)40V+ = +5V
V+ = +7V
V+ = +12V
V+ = +18V
10010100100010,000
EFFICIENCY vs. LOAD CURRENT
(2.5V, PWM MODE)MAX1761 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)40
V+ = +12V
V+ = +5V = VL
V+ = +7V
V+ = +18V
10010100100010,000
EFFICIENCY vs. LOAD CURRENT
(1.8V, SKIP MODE)MAX1761 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)40
V+ = +18VV+ = +12V
V+ = +7V
V+ = +5V = VL
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. INPUT VOLTAGE
(SKIP MODE)
MAX1761 toc10
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)
ON1 = VL, ON2 = VL
NO LOAD
20 μs/div
LOAD-TRANSIENT RESPONSE
(2.5A COMPONENTS, VOUT = 1.8V)MAX1761 toc14
A: VOUT, AC-COUPLED, 5mV/div
B: INDUCTOR CURRENT, 1A/div
C: DL1, 5V/div
OUTPUT OVERLOAD WAVEFORMS
(IOUT = 4V, VOUT = 2.5V)MAX1761 toc15
A: VOUT, 1V/div
B: INDUCTOR CURRENT, 2A/div
C: DL1, 2V/div
100 μs/div
STARTUP AND SHUTDOWN WAVEFORMS
(VOUT = 2.5V)MAX1761 toc17
A: VOUT, 2V/div
B: INDUCTOR CURRENT, 2A/div
C: DL1, 5V/div
500 μs/div
20 μs/div
LOAD-TRANSIENT RESPONSE
(2.5A COMPONENTS, VOUT = 2.5V)MAX1761 toc13
A: VOUT, AC-COUPLED, 10mV/div
B: INDUCTOR CURRENT, 1A/div
C: DL1, 5V/div
STARTUP AND SHUTDOWN WAVEFORMS
(VOUT = 1.8V)MAX1761 toc16
A: VOUT, 2V/div
B: INDUCTOR CURRENT, 2A/div
C: DL1, 5V/div
500 μs/div
SUPPLY CURRENT vs. INPUT VOLTAGE
(PWM MODE)
MAX1761 toc11
INPUT VOLTAGE (V)
SUPPLY CURRENT (mA)ON1 = VL, ON2 = FLOAT
NO LOAD
NO-LOAD SUPPLY CURRENT vs.
INPUT VOLTAGE (SHUTDOWN)
MAX1761 toc12
INPUT VOLTAGE (V)
SUPPLY CURRENT (
ON1 = GND, 0N2 = VL
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
PINNAMEFUNCTIONFB1Feed b ack Inp ut for the 2.5V P WM . C onnect FB1 to GN D for a fi xed 2.5V outp ut. C onnect a r esi sti ve
vol tag e- d i vi d er to FB1 to ad j ust OU T1 fr om 1V to 5.5V . FB1 r eg ul ates to 1V ( see Ad j usti ng V OUT secti on) .OUT1Output Voltage Connection for PWM1. OUT1 senses the output voltage to set the regulator on-time
and is connected internally to a 160kΩ feedback input in fixed-output mode.REF2V Reference Voltage Output. Bypass REF to GND with 0.1μF (min) capacitor. Can supply 50μA for
external loads.
When ON1 = High, Normal/Forced PWM Mode Selection and OUT2 On/Off Control Input
ON2 CONDITIONMODE SELECTEDLOW (ON2 < 0.5V)OUT1 is enabled in normal mode; OUT2 is shut down.
HIGH (2V < ON2 < VL)Both outputs are enabled in normal mode.ON2
FloatingBoth outputs are enabled in forced-PWM mode.
5V+Battery Voltage. V+ is the input for the VL regulator and DH gate drivers and is also used for PWM
one-shot timing.ON1On/Off Control Input. Drive ON1 high to enable the device. Drive ON1 low to enter micropower
shutdown mode. Both REF and VL are disabled in shutdown. ON1 may be pinstrapped to V+.OUT2Output Voltage Connection for PWM2. OUT2 senses the output voltage to set the regulator on-time
and is connected internally to a 160kΩ feedback input in fixed-output mode.FB2Feed b ack Inp ut for the 1.8V P WM . C onnect FB2 to GN D for a fi xed 1.8V outp ut. C onnect a r esi sti ve
vol tag e- d i vi d er to FB2 to ad j ust OU T2 fr om 1V to 5.5V . FB2 r eg ul ates to 1V ( see Ad j usti ng V OU T secti on) .DH2High-Side Gate Driver Output for PWM2. Swings between GND and V+.CS2Current-Sense Connection for PWM2. Connect CS2 to the drain of the low-side driver. Alternatively,
connect CS2 to the junction of the source of the low-side FET and a current-sense resistor to GND.DL2Low-Side Gate Driver Output for PWM2. DL2 swings between GND and VL.GNDCombined Power and Analog GroundVL
Linear Regulator Output. VL is the output of the 4.65V internal linear regulator, capable of supplying
25mA for external loads. The VL pin also serves as the supply input for the DL gate driver and the
analog/logic blocks. VL can be overdriven by an external 5V supply to improve efficiency. Bypass
VL to GND with a 4.7μF ceramic capacitor.DL1Low-Side Gate Driver Output for PWM1. DL1 swings between GND and VL.CS1Current-Sense Connection for PWM1. Connect CS1 to the drain of the low-side driver. Alternatively,
connect CS1 to the junction of the source of the low-side FET and a current-sense resistor to GND.DH1High-Side Gate Driver Output for PWM1. DH1 swings between GND and V+.
Pin Description
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
Typical Application CircuitThe typical application circuit in Figure 1 generates two
low-voltage rails for general-purpose use in notebook
and subnotebook computers (I/O supply, fixed CPU
core supply, DRAM supply). This DC-DC converter
steps down a battery or AC adapter voltage to voltages
from 1.0V to 5.5V with high efficiency and accuracy.
See Table 1 for a list of components for common appli-
cations. Table 2 lists component manufacturers.
Detailed DescriptionThe MAX1761 dual buck controller is designed for low-
voltage power supplies in notebook and subnotebook
computers. Maxim’s proprietary Quick-PWM pulse-
width modulation circuit (Figure 2) is specifically
designed for handling fast load steps while maintaining
a relatively constant operating frequency 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 preventing
problems caused by widely varying switching frequen-
cies in conventional constant-on-time and constant-off-
time PWM schemes.
This MAX1761 controls two synchronously rectified out-
puts with complementary N- and P-channel MOSFETs.
Using the P-channel for the high-side MOSFET elimi-
nates external boost capacitors and diodes, reducing
PC board area and cost. The MAX1761 can step down
input voltages from 5V to 20V, to outputs ranging from
1V to 5.5V on either output. Dual Mode feedback inputs
allow fixed output voltages of 2.5V and 1.8V for OUT1
and OUT2, respectively; or, a resistive voltage-divider
can be used to adjust the output voltages from 1V to
5.5V. Other appropriate applications for this device are
digital cameras, large PDAs, and handy-terminals.
V+ Input and VL +5V Logic SuppliesThe MAX1761 has a 5V to 20V input voltage supply
range. A linear regulator powers the control logic and
other internal circuitry from the input supply pin (V+).
The linear regulator’s 4.65V output is available at VL
and can supply 25mA to external circuitry. When used
as an external supply, bypass VL to GND with a 4.7µF
capacitor. VL is turned off when the device is in shut-
down, and drops to approximately 4V when the device
experiences an output voltage fault.
The MAX1761 includes an input undervoltage lockout
(UVLO) circuit that prevents the device from switching
until VL > 4.25V (max). UVLO ensures there is sufficient
drive for the external MOSFETs, prevents the high-side
MOSFET from being turned on for near 100% duty
cycle, and keeps the output in regulation. The UVLO
DL1
CS1
OUT1
DH1
FB1GND
ON2REF
DL2
OUT2
CS2
DH2
FB2ON1
2.5V+1.8V
220μF
10μF
7μH
4.7μF
0.1μF
7μH
LX2LX1
220μF
VOUT1
5V < VBATT < 20V
VOUT2
0.1μF
MAX1761
10Ω
Figure 1. Typical Application Circuit
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebookscomparator has 40mV hysteresis to prevent startup
oscillations on slowly rising input voltages.
If VL is not driven externally, then V+ should be at least
5V to ensure proper operation. If V+ is running from a
5V (±10%) supply, V+ should be externally connected
to VL. Overdriving the VL regulator with an external 5V
supply also increases the MAX1761’s efficiency.
Voltage Reference (REF)The internal 2V reference is accurate to ±1% (max)
over temperature and can supply a 50µA load current.
Bypass REF to GND with a 0.1µF capacitor when REF
is unloaded. Use a 0.22µF capacitor when applying an
external load.
Free-Running Constant-On-Time PWM
Controller with Input Feed-ForwardThe Quick-PWM control architecture is a constant-on-
time, current-mode type with voltage feed-forward
(Figure 3). This architecture relies on the output ripple
voltage to provide the PWM ramp signal. Thus, the out-
put filter capacitor’s ESR acts as a feedback resistor.
The control algorithm is simple: the high-side switch on-
time is determined solely by a one-shot whose period is
inversely proportional to input voltage and directly pro-
portional to output voltage (see the On-Time One-Shot
section). Another one-shot sets a minimum off-time
(400ns typical). The on-time one-shot is triggered if the
error comparator is low, the low-side switch current is
below the current-limit threshold, and the minimum off-
time one-shot has timed out.
Table 1. Component Selection for Standard Applications
COMPONENT2.5V AT 2.0A2.5V AT 3.5A1.8V AT 2.0A3.3V AT 2AInput Range5V to 18V5V to 18V5V to 18V5V to 18V
Frequency350kHz350kHz250kHz350kHz
Complementary
P- and N-Channel
MOSFETs
Fairchild FDS8958ASiliconix IRF7319Fairchild FDS8958AFairchild FDS8958A
Inductor
7μH
Sumida CDRH104-
7R0NC
3.5μH
Sumida CDRH127-
3R5NC
7μH
Sumida CDRH104-
7R0NC
10μH
Sumida CDRH104-
100NC
Input Capacitor
10μF, 25V
Taiyo Yuden
TMK432BJ106KM
2 x 10μF, 25V
Taiyo Yuden
TMK432BJ106KM
10μF, 25V
Taiyo Yuden
TMK432BJ106KM
10μF, 25V
Taiyo Yuden
TMK432BJ106KM
Output Capacitor
330μF, 10V
Kemet
T510X 337K101
2 x 330μF, 10V
Kemet
T510X 337K010
330μF, 10V
Kemet
T510X 337K010
330μF, 10V
Kemet
T510X 337K010
R1 = ShortR1 = 1kR3 = ShortR1 = ShortC urr ent- S ense
Feed b ack Resi stor sR2 = OpenR2 = 1kR4 = OpenR2 = Open
Table 2. Component Suppliers
SUPPLIERPHONEWEBFairchild
Semiconductor408-822-2181www.fairchildsemi.com
Kemet408-986-0424www.kemet.com
Panasonic847-468-5624ww w.p anasonic. com
Rohm760-929-2100www.rohmelectronics.
com
Sanyo619-661-6835www.secc.co.jp
Siliconix408-988-8000www.vishay.com
Sumida847-956-0666www.sumida.com
Taiyo Yuden408-573-4150www.t-yuden.com
MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
On-Time One-ShotThe heart of the PWM core is the one-shot that sets the
high-side switch on-time for both controllers. This fast,
low-jitter, adjustable one-shot includes circuitry that
varies the on-time in response to battery and output
voltage. The high-side switch on-time is inversely pro-
portional to the battery voltage as measured by the V+
input, and proportional to the output voltage. This algo-
rithm results in a nearly constant switching frequency
despite the absence of a fixed-frequency clock genera-
tor. The benefits of a constant switching frequency are
twofold: first, the switching noise occurs at a known fre-
quency and is easily filtered; second, the inductor rip-
ple current remains relatively constant, resulting in
predictable output voltage ripple and a relatively sim-
ple design procedure. The difference in frequencies
between OUT1 and OUT2 prevents audio-frequency
“beating” and minimizes crosstalk between the two
SMPS. The on-times can be calculated by using the
equation below that references the K values listed in
Table 3.
The 0.1V offset term accounts for the expected drop
across the low-side MOSFET switch.
On-Time = K V+ 0.1V
OUT_
OUT1OUT2
ON1ON2
CIN1CIN2
DL1DL2
DL1DL2
ZCC1ZCC2
ILIM1ILIM2VOSQ4Q3D2L2
COUT1COUT2
-0.1V-0.1V
PWM
CONTROL
BLOCK
PWM
CONTROL
BLOCK
LINEAR
REG
VREF
MAX1761
OUT1VL
DH1DH2DHDHDL
OUTOUT
GND
SHDNREF
CS1CS2
ILIMILIM
ZERO
CROSSING
ZERO
CROSSING
DL1DH2
ON1
DRIVERDRIVER
DRIVERDRIVER
OUT1VINVINCREF
VIN
ON1SHDN
VIN
REF
OUT2
ON2
Figure 2. Functional Diagram
Table 3. On-Time One-Shot
DEVICEK
(μs)
MIN
(kHz)
TYP
(kHz)
MAX
(kHz)OUT12.857318350428
OUT24.000227250278
MAX1761
Small, Dual, High-Efficiency
Buck Controller for NotebooksThe maximum on-time and minimum off-time, tOFF(MIN),
one-shots restrict the continuous-conduction output
voltage. The worst-case dropout performance occurs
with the minimum on-time and the maximum off-time, so
the worst-case duty cycle for VIN= 6V, VOUT1= 5V is
given by:
The duty cycle is ideally determined by the ratio of
input-to-output voltage (Duty Cycle = VOUT/VIN).
Voltage losses in the loop cause the actual duty cycle
to deviate from this relationship. See the Dropout
Performancesection for more information. Equate the
off-time duty cycle restriction to the nonideal input/out-
put voltage duty cycle ratio. Typical units will exhibit
better performance. Operation of any power supply in
dropout will greatly reduce the circuit’s transient
response, and some additional bulk capacitance may
be required to support fast load changes.
Resistive voltage drops in the inductor loop and the
dead-time effect cause switching-frequency variations.
Parasitic voltage losses decrease the effective voltage
applied to the inductor. The MAX1761 compensates by
shifting the duty cycle to maintain the regulated output
voltage. The resulting change in frequency is:
VDROP1is the sum of the parasitic voltage drops in the
inductor discharge path, including synchronous rectifi-
er, inductor, and PC board resistances; VDROP2is the
sum of the resistances in the charging path; and tONis
the on-time calculated by the MAX1761.
In forced PWM mode, the dead-time effect increases
the effective on-time, reducing the switching frequency
as one or both dead times. This occurs only at light or
negative loads when the inductor current reverses.
Under these conditions, the inductor’s EMF causes the
switching node of the inductor to go high during the
dead time, extending the effective on-time. V+V+V)
OUTDROP1INDROP2tDuty Cyclet t
ON(MIN)
ON(MIN) OFF(MAX)===2054054500804..%μ
sns
OUT
REF
UVP
FROM ZERO-CROSSING DETECTOR
FROM CURRENT-LIMIT COMPARATOR
ERROR
AMP
TOFF
TON
REF
-30%
FEEDBACK
MUX
(SEE FIGURE 12)
TO DL DRIVER INPUT
FROM OUT
FROM FEEDBACK
TO DH DRIVER INPUTON-TIME
COMPUTE
TON
1-SHOT
1-SHOT
1-SHOT
TRIG
TRIG
OUT
GAIN
DRIVER
TIMERSHDNSHDNON/OFF
CONTROL
VIN
UVP
LATCH
MAX1761
Figure 3. PWM Controller (One Side Only)
