Rainbow Electronics MAX8742 User Manual
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
General Description
The MAX8741/MAX8742 are buck-topology, step-down,
switch-mode, power-supply controllers that generate
logic-supply voltages in battery-powered systems. These
high-performance, dual/triple-output devices include onboard power-up sequencing, power-good signaling with
delay, digital soft-start, secondary winding control, lowdropout circuitry, internal frequency-compensation networks, and automatic bootstrapping.
Up to 97% efficiency is achieved through synchronous
rectification and Maxim’s proprietary Idle Mode™ control
scheme. Efficiency is greater than 80% over a 1000:1
load-current range, which extends battery life in system
suspend or standby mode. Excellent dynamic response
corrects output load transients within five clock cycles.
Strong 1A on-board gate drivers ensure fast external
n-channel MOSFET switching.
These devices feature a logic-controlled and synchronizable, fixed-frequency, pulse-width-modulation (PWM)
operating mode. This reduces noise and RF interference
in sensitive mobile communications and pen-entry applications. Asserting the SKIP pin enables fixed-frequency
mode, for lowest noise under all load conditions.
The MAX8741/MAX8742 include two PWM regulators,
adjustable from 2.5V to 5.5V with fixed 5.0V and 3.3V
modes. All these devices include secondary feedback
regulation, and the MAX8742 contains a 12V/120mA linear regulator. The MAX8741 includes a secondary feedback input (SECFB), plus a control pin (STEER) that
selects which PWM (3.3V or 5V) receives the secondary
feedback signal. SECFB provides a method for adjusting
the secondary winding voltage regulation point with an
external resistor-divider, and is intended to aid in creating
auxiliary voltages other than fixed 12V.
The MAX8741/MAX8742 contain internal output overvoltage- and undervoltage-protection features.
________________________Applications
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
Desktop CPU Local DC-DC Converters
Features
♦ 97% Efficiency
♦ 4.2V to 30V Input Range
♦ 2.5V to 5.5V Dual Adjustable Outputs
♦ Selectable 3.3V and 5V Fixed or Adjustable
Outputs (Dual Mode™)
♦ 12V Linear Regulator
♦ Adjustable Secondary Feedback (MAX8741)
♦ 5V/50mA Linear-Regulator Output
♦ Precision 2.5V Reference Output
♦ Programmable Power-Up Sequencing
♦ Power-Good (RESET) Output
♦ Output Overvoltage Protection
♦ Output Undervoltage Shutdown
♦ 333kHz/500kHz Low-Noise, Fixed-Frequency
Operation
♦ Low-Dropout, 98% Duty-Factor Operation
♦ 2.5mW Typical Quiescent Power (12V Input,
Both SMPSs On)
♦ 4µA Typical Shutdown Current
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
________________________________________________________________ Maxim Integrated Products 1
5V
LINEAR
12V
LINEAR
POWER-UP
SEQUENCE
POWER-
GOOD
3.3V
SMPS
5V
SMPS
RESETON/OFF
5V (RTC)
3.3V
INPUT
5V
12V
Functional Diagram
19-3262; Rev 0; 4/04
Ordering Information
Idle Mode is a trademark of Maxim Integrated Products, Inc.
Dual Mode is a trademark of Maxim Integrated Products, Inc.
Pin Configurations appear at end of data sheet.
PART
TEMP RANGE
PIN-PACKAGE
MAX8741EAI
28 SSOP
MAX8741ETJ
32 Thin QFN 5m m x 5m m
MAX8742EAI
28 SSOP
MAX8742ETJ
32 Thin QFN 5m m x 5m m
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(V+ = 15V, both PWMs on, SYNC = VL, VLload = 0, REF load = 0, SKIP = 0, TA= 0°C to +85°C, unless otherwise noted. Typical
values are at T
A
= +25°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.
V+ to GND..............................................................-0.3V to +36V
PGND to GND.....................................................................±0.3V
V
L
to GND ................................................................-0.3V to +6V
BST3, BST5 to GND ..............................................-0.3V to +36V
CSH3, CSH5 to GND................................................-0.3V to +6V
FB3 to GND..............................................-0.3V to (CSL3 + 0.3V)
FB5 to GND...............................................-0.3V to (CSL5 +0.3V)
LX3 to BST3..............................................................-6V to +0.3V
LX5 to BST5..............................................................-6V to +0.3V
REF, SYNC, SEQ, STEER, SKIP,
TIME/ON5, SECFB, RESET to GND ..........-0.3V to (V
L
+ 0.3V)
V
DD
to GND............................................................-0.3V to +20V
RUN/ON3, SHDN to GND.............................-0.3V to (V+ + 0.3V)
12OUT to GND ..........................................-0.3V to (V
DD
+ 0.3V)
DL3, DL5 to PGND........................................-0.3V to (V
L
+ 0.3V)
DH3 to LX3 ..............................................-0.3V to (BST3 + 0.3V)
DH5 to LX5 ..............................................-0.3V to (BST5 + 0.3V)
V
L
, REF Short to GND ................................................Momentary
12OUT Short to GND..................................................Continuous
REF Current...........................................................+5mA to -1mA
V
L
Current.........................................................................+50mA
12OUT Current . .............................................................+200mA
V
DD
Shunt Current............................................................+15mA
Continuous Power Dissipation (T
A
= +70°C)
28-Pin SSOP (derate 9.52mW/°C above +70°C) ........762mW
32-Pin Thin QFN (derate 21.3mW/°C above +70°C) ....1702mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range ............................-65°C to +160°C
Lead Temperature (soldering, 10s) ................................+300°C
PARAMETER CONDITIONS
UNITS
MAIN SMPS CONTROLLERS
Input Voltage Range 4.2
V
3V Output Voltage in Adjustable Mode
V+ = 4.2V to 30V, CSH3 - CSL3 = 0,
CSL3 connected to FB3
2.5
V
3V Output Voltage in Fixed Mode
V+ = 4.2V to 30V, 0 < CSH3 - CSL3
< 80mV, FB3 = 0
V
5V Output Voltage in Adjustable Mode
V+ = 4.2V to 30V, CSH5 - CSL5 = 0,
CSL5 connected to FB5
2.5
V
5V Output Voltage in Fixed Mode
V+ = 5.3V to 30V, 0 < CSH5 - CSL5
< 80mV, FB5 = 0
V
Output Voltage Adjust Range Either SMPS
5.5 V
Adjustable-Mode Threshold Voltage Dual-mode comparator 0.5 1.1 V
Load Regulation Either SMPS, 0 < CSH_ - CSL_ < 80mV -2 %
Line Regulation Either SMPS, 5.2V < V+ < 30V
%/V
CSH3 - CSL3 or CSH5 - CSL5 80 100
Current-Limit Threshold
SKIP = V
L
or VDD < 13V or SECFB < 2.44V -50
mV
Idle-Mode Threshold SKIP = 0, not tested 10 25 40 mV
Soft-Start Ramp Time
From enable to 95% full current limit with
respect to f
OSC
(Note 1)
512
Clks
SYNC = V
L
500
Oscillator Frequency
SYNC = 0
333
kHz
MIN TYP MAX
2.42
3.20 3.39 3.47
2.42
4.85 5.13 5.25
REF
0.03
450
283
-100 -150
30.0
2.58
2.58
120
550
383
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 15V, both PWMs on, SYNC = VL, VLload = 0, REF load = 0, SKIP = 0, TA= 0°C to +85°C, unless otherwise noted. Typical
values are at T
A
= +25°C.)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
SYNC = V
L
95 97
Maximum Duty Factor
SYNC = 0 (Note 2)
98
%
SYNC Input High Pulse Width Not tested
ns
SYNC Input Low Pulse Width Not tested
ns
SYNC Rise/Fall Time Not tested
ns
SYNC Input-Frequency Range
kHz
Current-Sense Input Leakage Current
V+ = V
L
= 0,
CSL3 = CSH3 = CSL5 = CSH5 = 5.5V
10 µA
FLYBACK CONTROLLER
VDD Regulation Threshold Falling edge (MAX8742) 13 14 V
SECFB Regulation Threshold Falling edge (MAX8741)
V
DL Pulse Width VDD < 13V or SECFB < 2.44V
µs
VDD Shunt Threshold Rising edge, hysteresis = 1% (MAX8742) 18 20 V
VDD Shunt Sink Current V
DD
= 20V (MAX8742) 10 mA
VDD Leakage Current V
DD
= 5V, off mode (Note 3) 30 µA
12V LINEAR REGULATOR (MAX8742)
12OUT Output Voltage 13V < V
DD
< 18V, 0 < I
LOAD
< 120mA
V
12OUT Current Limit 12OUT forced to 11V, V
DD
= 13V 150 mA
Quiescent V
DD
Current V
DD
= 18V, run mode, no 12OUT load 50
µA
INTERNAL REGULATOR AND REFERENCE
VL Output Voltage
SHDN = V+, RUN/ON3 = TIME/ON5 = 0,
5.4V < V+ < 30V, 0mA < I
LOAD
< 50mA
4.7 5.1 V
VL Undervoltage-Lockout Fault Threshold Falling edge, hysteresis = 1% 3.5 3.6 3.7 V
VL Switchover Threshold Rising edge of CSL5, hysteresis = 1% 4.2 4.5 4.7 V
REF Output Voltage No external load (Note 4)
2.5
V
0 < I
LOAD
< 50µA
REF Load Regulation
0 < I
LOAD
< 5mA
mV
REF Sink Current 10 µA
REF Fault-Lockout Voltage Falling edge 1.8 2.4 V
V+ Operating Supply Current VL switched over to CSL5, 5V SMPS on 5 50 µA
V+ Standby Supply Current
V+ = 5.5V to 30V, both SMPSs off, includes
current into SHDN
30 60 µA
V+ Standby Supply Current in Dropout
V+ = 4.2V to 5.5V, both SMPSs off, includes
current into SHDN
50
µA
V+ Shutdown Supply Current V+ = 4.0V to 30V, SHDN = 0 4 10 µA
MAX8742 2.5 4
Quiescent Power Consumption
Both SMPSs enabled,
FB3 = FB5 = 0,
CSL3 = CSH3 = 3.5V,
CSL5 = CSH5 = 5.3V
MAX8741 1.5 4
mW
96.5
200
200
400 583
0.01
2.44 2.60
0.75
11.65 12.10 12.50
2.45
200
100
2.55
12.5
100.0
200
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 15V, both PWMs on, SYNC = VL, VLload = 0, REF load = 0, SKIP = 0, TA= 0°C to +85°C, unless otherwise noted. Typical
values are at T
A
= +25°C.)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
FAULT DETECTION
Overvoltage Trip Threshold With respect to unloaded output voltage 4 7 10 %
Overvoltage Fault Propagation Delay
CSL_ driven 2% above overvoltage trip
threshold
1.5 µs
Output Undervoltage Threshold With respect to unloaded output voltage 60 70 80 %
Output Undervoltage-Lockout Time
From each SMPS enabled, with respect to
f
OSC
Clks
Thermal-Shutdown Threshold Typical hysteresis = 10°C
°C
RESET
RESET Trip Threshold
With respect to unloaded output voltage,
falling edge; typical hysteresis = 1%
-7
-4 %
RESET Propagation Delay
Falling edge, CSL_ driven 2% below RESET
trip threshold
1.5 µs
RESET Delay Time With respect to f
OSC
Clks
INPUTS AND OUTPUTS
Feedback-Input Leakage Current FB3, FB5; SECFB = 2.6V 1 50 nA
Logic Input-Low Voltage
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC
0.6 V
Logic Input-High Voltage
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC
2.4 V
Input Leakage Current
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
±1µA
Logic Output-Low Voltage RESET, I
SINK
= 4mA 0.4 V
Logic Output-High Current RESET = 3.5V 1 mA
TIME/ON5 Input Trip Level SEQ = 0 or V
L
2.4 2.6 V
TIME/ON5 Source Current TIME/ON5 = 0, SEQ = 0 or V
L
2.5 3 3.5 µA
TIME/ON5 On-Resistance TIME/ON5; RUN/ON3 = 0, SEQ = 0 or V
L
15 80 Ω
Gate-Driver Sink/Source Current DL3, DH3, DL5, DH5; forced to 2V 1 A
SSOP package 1.5 7
Gate-Driver On-Resistance
QFN package 1.5 8
Ω
3300 4096 4700
+150
-5.5
27,000 32,000 37,000
SHDN, STEER, SYNC, SEQ; V
High or low (Note 5)
= 0V or 3.3V
PIN
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS
(V+ = 15V, both PWMs on, SYNC = VL, VLload = 0, REF load = 0, SKIP = 0, TA= -40°C to +85°C, unless otherwise noted.) (Note 6)
PARAMETER CONDITIONS
UNITS
MAIN SMPS CONTROLLERS
Input Voltage Range 4.2
V
3V Output Voltage in Adjustable Mode
V+ = 4.2V to 30V, CSH3 - CSL3 = 0,
CSL3 connected to FB3
V
3V Output Voltage in Fixed Mode
V+ = 4.2V to 30V, 0 < CSH3 - CSL3
< 80mV, FB3 = 0
V
5V Output Voltage in Adjustable Mode
V+ = 4.2V to 30V, CSH5 - CSL5 = 0,
CSL5 connected to FB5
V
5V Output Voltage in Fixed Mode
V+ = 5.3V to 30V, 0 < CSH5 - CSL5
< 80mV, FB5 = 0
V
Output Voltage Adjust Range Either SMPS
5.5 V
Adjustable-Mode Threshold Voltage Dual-mode comparator 0.5 1.1 V
CSH3 - CSL3 or CSH5 - CSL5 80
Current-Limit Threshold
SKIP = V
L
or VDD < 13V or SECFB < 2.44V -50
mV
SYNC = V
L
Oscillator Frequency
SYNC = 0
kHz
SYNC = V
L
95
Maximum Duty Factor
SYNC = 0 (Note 2) 97
%
SYNC Input Frequency Range
kHz
FLYBACK CONTROLLER
VDD Regulation Threshold Falling edge (MAX8742) 13 14 V
SECFB Regulation Threshold Falling edge (MAX8741)
V
VDD Shunt Threshold Rising edge, hysteresis = 1% (MAX8742) 18 20 V
VDD Shunt Sink Current V
DD
= 20V (MAX8742) 10 mA
12V LINEAR REGULATOR (MAX8742)
12OUT Output Voltage 13V < V
DD
< 18V, 0mA < I
LOAD
< 100mA
V
Quiescent V
DD
Current V
DD
= 18V, run mode, no 12OUT load
µA
INTERNAL REGULATOR AND REFERENCE
VL Output Voltage
SHDN = V+, RUN/ON3 = TIME/ON5 = 0,
5.4V < V+ < 30V, 0 < I
LOAD
< 50mA
4.7 5.1 V
VL Undervoltage-Lockout Fault Threshold Falling edge, hysteresis = 1% 3.5 3.7 V
VL Switchover Threshold Rising edge of CSL5, hysteresis = 1% 4.2 4.7 V
REF Output Voltage No external load (Note 4)
V
0 < I
LOAD
< 50µA
REF Load Regulation
0 < I
LOAD
< 5mA
mV
REF Sink Current 10 µA
REF Fault-Lockout Voltage Falling edge 1.8 2.4 V
V+ Operating Supply Current VL switched over to CSL5, 5V SMPS on 50 µA
MIN TYP MAX
2.42 2.58
3.20 3.47
2.42 2.58
4.85 5.25
REF
450 550
283 383
400 583
2.44 2.60
11.65 12.50
2.45 2.55
30.0
120
-150
100
12.5
100.0
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
6 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 15V, both PWMs on, SYNC = VL, VLload = 0, REF load = 0, SKIP = 0, TA= -40°C to +85°C, unless otherwise noted.) (Note 6)
PARAMETER CONDITIONS
MIN
TYP
MAX
UNITS
V+ Standby Supply Current
V+ = 5.5V to 30V, both SMPSs off, includes
current into SHDN
60 µA
V+ Standby Supply Current in Dropout
V+ = 4.2V to 5.5V, both SMPSs off, includes
current into SHDN
µA
V+ Shutdown Supply Current V+ = 4.0V to 30V, SHDN = 0 10 µA
MAX8742 4
Quiescent Power Consumption
Both SMPSs enabled,
FB3 = FB5 = 0,
MAX8741 4
mW
FAULT DETECTION
Overvoltage Trip Threshold With respect to unloaded output voltage 4 10 %
Output Undervoltage Threshold With respect to unloaded output voltage 60 80 %
Output Undervoltage-Lockout Time
From each SMPS enabled, with respect to
f
OSC
Clks
RESET
RESET Trip Threshold
With respect to unloaded output voltage,
falling edge; typical hysteresis = 1%
-7 -4 %
RESET Delay Time With respect to f
OSC
Clks
INPUTS AND OUTPUTS
Feedback-Input Leakage Current FB3, FB5; SECFB = 2.6V 50 nA
Logic Input-Low Voltage
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC
0.6 V
Logic Input-High Voltage
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC
2.4 V
Logic Output-Low Voltage RESET, I
SINK
= 4mA 0.4 V
Logic Output-High Current RESET = 3.5V 1 mA
TIME/ON5 Input Trip Level SEQ = 0 or V
L
2.4 2.6 V
TIME/ON5 Source Current TIME/ON5 = 0, SEQ = 0 or V
L
2.5 3.5 µA
TIME/ON5 On-Resistance TIME/ON5; RUN/ON3 = 0, SEQ = 0 or V
L
80 Ω
SSOP package 7
Gate-Driver On-Resistance
QFN package 8
Ω
Note 1: Each of the four digital soft-start levels is tested for functionality; the steps are typically in 20mV increments.
Note 2: High duty-factor operation supports low input-to-output differential voltages, and is achieved at a lowered operating frequency
(see the Dropout Operation section).
Note 3: Off mode for the MAX8742 12V linear regulator occurs when the SMPS that has flyback feedback (V
DD
) steered to it is disabled.
In situations where the main outputs are being held up by external keep-alive supplies, turning off the 12OUT regulator prevents
a leakage path from the output-referred flyback winding, through the rectifier, and into V
DD
.
Note 4: Since the reference uses V
L
as its supply, the reference’s V+ line-regulation error is insignificant.
Note 5: Production testing limitations due to package handling require relaxed maximum on-resistance specifications for the thin
QFN package. The SSOP and thin QFN packages contain the same die, and the thin QFN package imposes no additional
resistance in circuit.
Note 6: Specifications from 0°C to -40°C are guaranteed by design, not production tested.
200
CSL3 = CSH3 = 3.5V,
CSL5 = CSH5 = 5.3V
High or low (Note 5)
3300 4700
27,000 37,000
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
_______________________________________________________________________________________ 7
100
50
0.001 0.01 0.1 1 10
EFFICIENCY vs. 5V OUTPUT CURRENT
60
MAX8741/42 toc01
5V OUTPUT CURRENT (A)
EFFICIENCY (%)
70
80
90
85
75
65
55
95
ON5 = 5V
ON3 = 0V
f = 500kHz
MAX8741
V+ = 15V
V+ = 6V
100
50
0.001 0.01 0.1 1 10
EFFICIENCY vs. 3.3V OUTPUT CURRENT
60
MAX8741/42 toc02
3.3V OUTPUT CURRENT (A)
EFFICIENCY (%)
70
80
90
85
75
65
55
95
ON5 = ON3 = 5V
f = 500kHz
MAX8741
V+ = 15V
V+ = 6V
800
600
400
200
0
01051520
MAXIMUM VDD OUTPUT CURRENT
vs. INPUT VOLTAGE
MAX8741/42 toc03
INPUT VOLTAGE (V)
MAXIMUM V
DD
OUTPUT CURRENT (mA)
5V LOAD = 0
5V LOAD = 3A
100
0.01
01052030
NO-LOAD INPUT CURRENT
vs. INPUT VOLTAGE
0.1
1
10
MAX8741/42 toc04
INPUT VOLTAGE (V)
INPUT CURRENT (mA)
15 25
SKIP = 0V
SKIP = V
L
ON5 = ON3 = 5V
NO LOAD
10,000
1
01052030
V+ STANDBY INPUT CURRENT
vs. INPUT VOLTAGE
10
100
1000
MAX8741/42 toc05
INPUT VOLTAGE (V)
INPUT CURRENT (µA)
15 25
ON5 = ON3 = 0V
NO LOAD
0
2
6
4
8
10
010515202530
SHUTDOWN INPUT CURRENT
vs. INPUT VOLTAGE
MAX8741/42 toc06
INPUT VOLTAGE (V)
INPUT CURRENT (µA)
SHDN = 0V
0.001 0.01 1
MINIMUM VIN TO V
OUT
DIFFERENTIAL
vs. 5V OUTPUT CURRENT
MAX8741/42 toc07
5V OUTPUT CURRENT (A)
MINIMUM V
IN
TO V
OUT
DIFFERENTIAL (mV)
1000
10
100
0.1 10
f = 500kHz
f = 333kHz
V
OUT
> 4.8V
1000
0.1
0.001 0.01 1 10
SWITCHING FREQUENCY
vs. LOAD CURRENT
1
10
100
MAX8741/42 toc08
LOAD CURRENT (A)
SWITCHING FREQUENCY (kHz)
0.1
3.3V, VIN = 15V
5V, VIN = 15V
3.3V, VIN = 6.5V
5V, VIN = 6.5V
4.90
4.92
4.96
4.94
4.98
5.00
02010 30 40 50
VL REGULATOR OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX8741/42 toc09
OUTPUT CURRENT (mA)
V
L
OUTPUT VOLTAGE (V)
VIN = 15V
ON3 = ON5 = 0V
Typical Operating Characteristics
(Circuit of Figure 1, Table 1, 6A/500kHz components, TA = +25°C, unless otherwise noted.)
5V LOAD-TRANSIENT RESPONSE
MAX8741/42 toc11
10V
0
5A
0
I
LX5
5A/div
V
LX5
10V/div
5V OUTPUT
5OmV/div
AC-COUPLED
20µs/div
V
IN
= 8V, I
OUT
= 1A TO 5A
3.3V LOAD-TRANSIENT RESPONSE
MAX8741/42 toc12
10V
0
5A
0
I
LX3
5A/div
V
LX3
10V/div
3.3V OUTPUT
5OmV/div
AC-COUPLED
20µs/div
V
IN
= 8V, I
OUT
= 1A TO 5A
SHUTDOWN WAVEFORMS
MAX8741/42 toc14
5V
3.3V
0
0
0
5V OUTPUT
2V/div
3.3V OUTPUT
2V/div
DL3
5V/div
DL5
5V/div
SHDN
5V/div
500µs/div
R
LOAD3
= 5Ω, R
LOAD5
= 5Ω
STARTUP WAVEFORMS
MAX8741/42 toc13
0
0
0
0
3.3V OUTPUT
2V/div
5V OUTPUT
5V/div
TIME
2V/div
RUN
5V/div
2ms/div
SEQ = V
L
, O.O1µF CAPACITOR ON-TIME
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(Circuit of Figure 1, Table 1, 6A/500kHz components, TA = +25°C, unless otherwise noted.)
2.505
2.500
2.495
2.490
2.485
0312 456
REF OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX8741/42 toc10
OUTPUT CURRENT (mA)
REF OUTPUT VOLTAGE (V)
VIN = 15V
ON3 = ON5 = 0
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
_______________________________________________________________________________________ 9
Pin Description
PIN
SSOP TQFN
NAME FUNCTION
129CSH3 Current-Sense Input for the 3.3V SMPS. Current-limit level is 100mV referred to CSL3.
230CSL3 Current-Sense Input. Also serves as the feedback input in fixed-output mode.
331FB3
Feedback Input for the 3.3V SMPS. Regulates at FB3 = REF (approximately 2.5V) in
adjustable mode. FB3 is a dual-mode input that also selects the 3.3V fixed outputvoltage setting when connected to GND. Connect FB3 to a resistor-divider for
adjustable-output mode.
12OUT
(MAX8742)
12V/120mA Linear-Regulator Output. Input supply comes from VDD. Bypass 12OUT to
GND with 1µF (min).
41
STEER
(MAX8741)
Logic-Control Input for Secondary Feedback. Selects the PWM that uses a transformer
and secondary feedback signal (SECFB):
STEER = GND: 3.3V SMPS uses transformer
STEER = V
L
: 5V SMPS uses transformer
V
DD
(MAX8742)
Supply Voltage Input for the 12OUT Linear Regulator. Also connects to an internal
resistor-divider for secondary winding feedback and to an 18V overvoltage shunt
regulator clamp.
52
SECFB
(MAX8741)
Secondary Winding Feedback Input. Normally connected to a resistor-divider from an
auxiliary output. SECFB regulates at V
SECFB
= 2.5V (see the Secondary Feedback
Regulation Loop section). Connect to V
L
if not used.
63SYNC
Oscillator Synchronization and Frequency Select. Connect to V
L
for 500kHz operation;
connect to GND for 333kHz operation. Can be driven at 400kHz to 583kHz for external
synchronization.
74TIME/ON5
Dual-Purpose Timing Capacitor Pin and ON/OFF Control Input. See the Power-Up
Sequencing and ON/
OFF
Controls section.
85GND Low-Noise Analog Ground and Feedback Reference Point
97 REF 2.5V Reference Voltage Output. Bypass to GND with 1µF (min).
10 8 SKIP Log i c- C ontr ol Inp ut that D i sab l es Id l e M od e w hen H i g h. C onnect to G N D for nor m al use.
11 9 RESET
Active-Low Timed Reset Output. RESET swings GND to V
L
. Goes high after a fixed
32,000 clock-cycle delay following power-up.
12 10 FB5
Feedback Input for the 5V SMPS. Regulates at FB5 = REF (approximately 2.5V) in
adjustable mode. FB5 is a dual-mode input that also selects the 5V fixed outputvoltage setting when connected to GND. Connect FB5 to a resistor-divider for
adjustable-output mode.
13 11 CSL5
C ur r ent- S ense Inp ut for the 5V S M P S . Al so ser ves as the feed b ack i np ut i n fi xed - outp ut
m od e, and as the b ootstr ap sup p l y i np ut w hen the vol tag e on C S L5/V
L
i s > 4.5V .
14 12 CSH5 Current-Sense Input for the 5V SMPS. Current-limit level is 100mV referred to CSL5.
MAX8741/MAX8742
500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
10 ______________________________________________________________________________________
Pin Description (continued)
PIN
SSOP TQFN
NAME FUNCTION
15 13 SEQ
Pin-Strap Input that Selects the SMPS Power-Up Sequence:
SEQ = GND: 5V before 3.3V, RESET output determined by both outputs
SEQ = REF: Separate ON3/ON5 controls, RESET output determined by 3.3V
output
SEQ = V
L
: 3.3V before 5V, RESET output determined by both outputs
16 14 DH5
Gate-Drive Output for the 5V, High-Side N-Channel Switch. DH5 is a floating driver
output that swings from LX5 to BST5, riding on the LX5 switching-node voltage.
17 15 LX5 Switching-Node (Inductor) Connection. Can swing 2V below ground without hazard.
18 17 BST5 Boost Capacitor Connection for High-Side Gate Drive (0.1µF)
19 18 DL5 Gate-Drive Output for the Low-Side Synchronous-Rectifier MOSFET. Swings 0 to VL.
20 19 PGND Power Ground
21 20 V
L
5V Internal Linear-Regulator Output. VL is also the supply-voltage rail for the chip.
After the 5V SMPS output has reached 4.5V (typ), V
L
automatically switches to the
output voltage through CSL5 for bootstrapping. Bypass to GND with 4.7µF. V
L
supplies up to 25mA for external loads.
22 21 V+
Battery Voltage Input, 4.2V to 30V. Bypass V+ to PGND close to the IC with a 0.22µF
capacitor. Connects to a linear regulator that powers V
L
.
23 22 SHDN
Shutdown Control Input, Active Low. Logic threshold is set at approximately 1V. For
automatic startup, connect SHDN to V+ through a 220kΩ resistor and bypass SHDN to
GND with a 0.01µF capacitor.
24 23 DL3 Gate-Drive Output for the Low-Side Synchronous-Rectifier MOSFET. Swings 0 to VL.
25 24 BST3 Boost Capacitor Connection for High-Side Gate Drive (0.1µF)
26 26 LX3 Switching-Node (Inductor) Connection. Can swing 2V below ground without hazard.
27 27 DH3
Gate-Drive Output for the 3.3V, High-Side N-Channel Switch. DH3 is a floating driver
output that swings from LX3 to BST3, riding on the LX3 switching-node voltage.
28 28 RUN/ON3 ON/OFF Control Input. See the Power-Up Sequencing and ON/
OFF
Controls section.
—
N.C. No Connection
6, 16, 25, 32
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