19-1835; Rev 0; 10/00
IT
TION K
VALUA
E
BLE
AVAILA
Small, Dual, High-Efficiency
Buck Controller for Notebooks
General Description
Features
o
Free-Running On-Demand PWM
o
Selectable Light-Load Pulse-Skipping Operation
o
±1% Total DC Error in Forced-PWM Mode
o
5V to 20V Input Range
o
Flexible 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
Adjustable
o
Output Undervoltage Protection
o
Complementary Synchronous Buck
o
No Current-Sense Resistor
o
4.65V at 25mA Linear Regulator Output
o
4µA V+ Shutdown Supply Current
o
5µA VL Shutdown Supply Current
o
950µA Quiescent Supply Current
o
Tiny 16-Pin QSOP Package
MAX1761
The 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.
Ordering Information
PART
MAX1761EEE
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
16 QSOP
________________________Applications
Notebooks and PDAs
Digital Cameras
Handy-Terminals
Smart Phones
1.8V/2.5V Logic and I/O Supplies
TOP VIEW
FB1 1
OUT1 2
REF 3
ON2 4
V+ 5
ON1 6
OUT2 7
Pin Configuration
16 DH1
15 CS1
14 DL1
MAX1761
13 VL
12 GND
11 DL2
10 CS2
9
DH2
Quick-PWM and Dual Mode are trademarks of
Maxim Integrated Products.
FB2 8
QSOP
1
________________________________________________________________
Maxim Integrated Products
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Small, Dual, High-Efficiency
Buck Controller for Notebooks
MAX1761
ABSOLUTE MAXIMUM RATINGS
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
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.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V+ = 15V, C
VL
= 4.7µF, C
REF
= 0.1µF, VL not externally driven unless otherwise noted,
T
A
= 0°C to +85°C,
unless
otherwise noted.) (Note 1)
PARAMETER
PWM CONTROLLERS
Input Voltage Range
DC Output Voltage Accuracy
(Note 3)
Output Voltage Adjust Range
OUT_ Input Resistance
FB_ Input Bias Current
CS_ Input Bias Current
Soft-Start Ramp Time
On-Time (Note 4)
Minimum Off-Time (Note 4)
BIAS AND REFERENCE
IL
Quiescent Supply Current
I+
IL
I+
VL
V
REF
I
REF
FB1 = FB2 = GND, VL = 5V, V
OUT1
and
V
OUT2
forced above regulation point
FB1 = FB2 = GND, V
OUT1
and V
OUT2
forced
above regulation point
VL undriven
VL = 5V
0.60
0.95
0.38
5
4
4.5
1.98
10
1.6
1.94
4.65
2
1.20
1.70
mA
0.65
10
10
4.75
2.02
8
µA
µA
V
V
mV
µA
V
mA
t
ON
t
OFF
V
FB_
= 1V, VL = 5V
V
CS_
= 0, VL = 5V
Zero to full ILIM
V+ = 10V, V
OUT1
= 2.5V,
V
OUT2
= 1.8V
OUT1
OUT2
661
648
V+
V
OUT_
(Note 2)
V+ = 4.5V to 20V,
VL = 4.75V to 5.25V,
ON2 = VL
FB_ = OUT_
FB1 = GND
FB2 = GND
4.5
0.99
2.475
1.782
1
80
-0.1
-1
1700
735
720
400
809
792
500
160
1
2.5
1.8
20
1.01
2.525
1.818
5.5
300
0.1
1
V
kΩ
µA
µA
µs
ns
ns
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Shutdown Supply Current
VL Output Voltage
Reference Voltage
Reference Load Regulation
REF Sink Current
REF Fault Lockout Voltage
VL = 5V, ON1 = ON2 = GND
VL = 0, 5V
I
LOAD
= 0 to 25mA, V+ = 5V to 20V
V+ = 5V to 20V, no load
I
REF
= 0 to 50µA
REF in regulation
Falling edge
Rising edge
2
_______________________________________________________________________________________
Small, Dual, High-Efficiency
Buck Controller for Notebooks
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, C
VL
= 4.7µF, C
REF
= 0.1µF, VL not externally driven unless otherwise noted,
T
A
= 0°C to +85°C,
unless
otherwise noted.) (Note 1)
PARAMETER
FAULT PROTECTION
Output Undervoltage Threshold
(Foldback)
Output Undervoltage Blanking
Time
Current-Limit Threshold
Thermal Shutdown Threshold
VL Undervoltage Lockout
Threshold
GATE DRIVERS
DH_ Gate Driver On-Resistance
(Pullup)
DH_ Gate Driver On-Resistance
(Pulldown)
DL_ Gate Driver On-Resistance
(Pullup)
DL_ Gate Driver On-Resistance
(Pulldown)
DH_ Gate Driver Source/Sink
Current
DL_ Gate Drive Sink Current
DL_ Gate Drive Source Current
LOGIC CONTROLS
ON_ Logic Input High Voltage
ON2 Logic Input Float Voltage
(Forced-PWM Mode)
ON_ Logic Input Low Voltage
ON1 Logic Input Current
ON2 Logic High Input Current
ON2 Logic Low Input Current
FB_ Dual Mode Threshold
V
ON2
> 2.0V
V
ON2
< 0.5V, V
ON1
> 2.0V
-1
0
-2
50
1
-1
100
2.0V < V
ON1
< VL
2.05
1.3
1.7
1.95
0.5
1
3
0
150
V
V
V
µA
µA
µA
mV
V+ = 6V to 20V, DH_, high state
DH_, low state
DL_ , high state
DL_, low state
V
DH_
= 3V, V+ = 6V
V
DL_
= 2.5V
V
DL_
= 2.5V
3.7
6.2
3.4
2.0
0.6
0.9
0.5
8
10
8
5
Ω
Ω
Ω
Ω
A
A
A
V
VL,UVLO
V
FB,UVFB
With respect to the regulation point, no load
60
10
92
-135
100
-120
2.5
160
4.1
4.4
o
MAX1761
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
70
80
32
108
-105
%
ms
V
FB,UVLO(t)
Measured from ON_ signal going high
GND - CS_, positive direction
GND - CS_, negative direction, ON2 = floating
GND - CS_, zero crossing, ON2 = 5V
Hysteresis = 10 C
Rising edge, hysteresis = 20mV, PWM is
disabled below this voltage
o
mV
C
V
_______________________________________________________________________________________
3
Small, Dual, High-Efficiency
Buck Controller for Notebooks
MAX1761
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V+ = 15V, C
VL
= 4.7µF, C
REF
= 0.1µF, VL not externally driven unless otherwise noted,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
PWM CONTROLLERS
Input Voltage Range
DC Output Voltage Accuracy
(Note 3)
Output Voltage Adjust Range
OUT_ Input Resistance
FB_ Input Bias Current
CS_ Input Bias Current
Soft-Start Ramp Time
On-Time (Note 4)
Minimum Off-Time (Note 4)
BIAS AND REFERENCE
IL
Quiescent Supply Current
I+
IL
I+
VL
V
REF
I
REF
FB1 = FB2 = GND, VL = 5V, V
OUT1
and
V
OUT2
forced above regulation point
FB1 = FB2 = GND, V
OUT1
and V
OUT2
forced above
regulation point
VL undriven
VL = 5V
1.2
1.7
0.5
10
10
4.5
1.98
10
4.75
2.02
8
µA
µA
V
V
mV
µA
mA
t
ON
t
OFF
V
FB_
= 1V, VL = 5V
V
CS_
= 0, VL = 5V
Zero to full ILIM
V+ = 10V, V
OUT1
= 2.5V,
V
OUT2
= 1.8V
Above regulation point
OUT1
OUT2
661
648
809
792
500
V+
VL
V
OUT_
(Note 2)
VL externally driven (Note 2)
V+ = 4.5V to 20V,
VL = 4.75V to 5.25V,
ON2 = VL
FB_ = OUT_
FB1 = GND
FB2 = GND
4.5
4.75
0.99
2.475
1.782
1
80
-0.1
-1
20
5.25
1.01
2.525
1.818
5.5
300
0.1
1
V
kΩ
µA
µA
µs
ns
ns
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
mA
Shutdown Supply Current
VL Output Voltage
Reference Voltage
Reference Load Regulation
REF Sink Current
FAULT PROTECTION
Output Undervoltage Threshold
(Foldback)
Output Undervoltage Lockout
Timer
Current-Limit Threshold
VL Undervoltage Lockout
Threshold
VL = 5V, ON1 = ON2 = GND
VL = 0, 5V
I
LOAD
= 0 to 25mA, V+ = 5V to 20V
V+ = 5V to 20V, no load
I
REF
= 0 to 50µA
REF in regulation
V
FB,UVFB
With respect to the regulation point, no load
60
10
92
-135
4.1
80
32
108
-105
4.4
%
ms
mV
V
V
FB,UVLO(t)
Measured from ON_ signal going high
GND – CS_, positive direction
GND – CS_, negative direction, ON2 = floating
V
VL,UVLO
Rising edge, hysteresis = 20mV, PWM is
disabled below this voltage
4
_______________________________________________________________________________________
Small, Dual, High-Efficiency
Buck Controller for Notebooks
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, C
VL
= 4.7µF, C
REF
= 0.1µF, VL not externally driven unless otherwise noted,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 1)
PARAMETER
GATE DRIVERS
DH_ Gate Driver On-Resistance
(Pullup)
DH_ Gate Driver On-Resistance
(Pulldown)
DL_ Gate Driver On-Resistance
(Pullup)
DL_ Gate Driver On-Resistance
(Pulldown)
DH_ Gate Driver Source/Sink
Current
DL_ Gate Drive Sink Current
DL_ Gate Driver Source Current
LOGIC CONTROLS
ON_ Logic Input High Voltage
ON2 Logic Input Float Voltage
(Forced-PWM Mode)
ON_ Logic Input Low Voltage
ON1 Logic Input Current
ON2 Logic High Input Current
ON2 Logic Low Input Current
FB_ Dual Mode Threshold
V
ON2
> 2.0V
V
ON2
< 0.5V, V
ON1
> 2.0V
-1
0
-2
50
V
ON1
> 2.0V
2.05
1.3
1.95
0.5
1
3
0
150
V
V
V
µA
µA
µA
mV
V+ = 6V to 20V, DH_, high state
DH_, low state
DL_, high state
DL_, low state
V
DH_
= 3V, V+ = 6V
V
DL_
= 2.5V
V
DL_
= 2.5V
8
10
8
5
Ω
Ω
Ω
Ω
A
A
A
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1761
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, C
DH
= 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.
_______________________________________________________________________________________
5
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