19-0480; Rev 4; 8/05
KIT
ATION
EVALU
LE
B
A
IL
A
AV
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
____________________________Features
The MAX1630–MAX1635 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 96% 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 systemsuspend or standby mode. Excellent dynamic response
corrects output load transients caused by the latest
dynamic-clock CPUs within five 300kHz 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 MAX1630–MAX1635 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 MAX1630/MAX1632/MAX1633/
MAX1635 each contain 12V/120mA linear regulators. The
MAX1631/MAX1634 include 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 MAX1630/MAX1631/MAX1632 contain internal output overvoltage and undervoltage protection features.
♦
♦
♦
♦
________________________Applications
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
♦
96% 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
(MAX1631/MAX1634)
5V/50mA Linear Regulator Output
Precision 2.5V Reference Output
Programmable Power-Up Sequencing
Power-Good (RESET) Output
Output Overvoltage Protection
(MAX1630/MAX1631/MAX1632)
Output Undervoltage Shutdown
(MAX1630/MAX1631/MAX1632)
200kHz/300kHz Low-Noise, Fixed-Frequency
Operation
Low-Dropout, 99% Duty-Factor Operation
2.5mW Typical Quiescent Power (+12V input, both
SMPSs on)
4μA Typical Shutdown Current
28-Pin SSOP Package
_______________Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX1630CAI
PART
0°C to +70°C
28 SSOP
MAX1630CAI+
0°C to +70°C
28 SSOP
MAX1630EAI+
-40°C to +85°C
28 SSOP
Ordering Information continued at end of data sheet.
+ Denotes lead-free package.
________________Functional Diagram
INPUT
+12V
+5V (RTC)
Notebook and Subnotebook Computers
5V
LINEAR
12V
LINEAR
3.3V
SMPS
5V
SMPS
POWER-UP
SEQUENCE
POWERGOOD
PDAs and Mobile Communicators
Desktop CPU Local DC-DC Converters
+3.3V
+5V
Pin Configurations and Selector Guide appear at end of data
sheet.
ON/OFF
Idle Mode and Dual Mode are trademarks of Maxim Integrated
Products.
RESET
________________________________________________________________ Maxim Integrated Products
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.
1
MAX1630–MAX1635
________________General Description
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
ABSOLUTE MAXIMUM RATINGS
V+ to GND ..............................................................-0.3V to +36V
PGND to GND.....................................................................±0.3V
VL to GND ................................................................-0.3V to +6V
BST3, BST5 to GND ...............................................-0.3V to +36V
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 +6V
VDD to GND ............................................................-0.3V to +20V
RUN/ON3, SHDN to GND.............................-0.3V to (V+ + 0.3V)
12OUT to GND ...........................................-0.3V to (VDD + 0.3V)
DL3, DL5 to PGND........................................-0.3V to (VL + 0.3V)
DH3 to LX3 ...............................................-0.3V to (BST3 + 0.3V)
DH5 to LX5 ...............................................-0.3V to (BST5 + 0.3V)
VL, REF Short to GND ................................................Momentary
12OUT Short to GND..................................................Continuous
REF Current...........................................................+5mA to -1mA
VL Current.........................................................................+50mA
12OUT Current ...............................................................+200mA
VDD Shunt Current ............................................................+15mA
Operating Temperature Ranges
MAX163_CAI.......................................................0°C to +70°C
MAX163_EAI ....................................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +160°C
Continuous Power Dissipation (TA = +70°C)
SSOP (derate 9.52mW/°C above +70°C) ....................762mW
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
(V+ = 15V, both PWMs on, SYNC = VL, VL load = 0mA, REF load = 0mA, SKIP = 0V, TA = TMIN to TMAX, unless otherwise noted.
Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
30.0
V
MAIN SMPS CONTROLLERS
Input Voltage Range
4.2
3V Output Voltage in
Adjustable Mode
V+ = 4.2V to 30V, CSH3–CSL3 = 0V,
CSL3 tied to FB3
2.42
2.5
2.58
V
3V Output Voltage in Fixed Mode
V+ = 4.2V to 30V, 0mV < CSH3–CSL3 < 80mV,
FB3 = 0V
3.20
3.39
3.47
V
5V Output Voltage in
Adjustable Mode
V+ = 4.2V to 30V, CSH5–CSL5 = 0V,
CSL5 tied to FB5
2.42
2.5
2.58
V
5V Output Voltage in Fixed Mode
V+ = 5.2V to 30V, 0mV < CSH–CSL5 < 80mV,
FB5 = 0V
4.85
5.13
5.25
V
Output Voltage Adjust Range
Either SMPS
REF
5.5
V
Adjustable-Mode Threshold Voltage
Dual Mode comparator
0.5
1.1
Load Regulation
Either SMPS, 0V < CSH_–CSL_ < 80mV
Line Regulation
Either SMPS, 5.2V < V+ < 30V
-2
0.03
%/V
CSH3–CSL3 or CSH5–CSL5
80
100
120
SKIP = VL or VDD < 13V or SECFB < 2.44V
-50
-100
-150
Idle Mode Threshold
SKIP = 0V, not tested
10
25
40
Soft-Start Ramp Time
From enable to 95% full current limit with respect to
fOSC (Note 1)
Current-Limit Threshold
Oscillator Frequency
Maximum Duty Factor
2
512
mV
mV
Clk
SYNC = VL
270
300
330
SYNC = 0V
170
200
230
SYNC = VL
97
98
SYNC = 0V (Note 2)
98
99
_______________________________________________________________________________________
V
%
kHz
%
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
(V+ = 15V, both PWMs on, SYNC = VL, VL load = 0mA, REF load = 0mA, SKIP = 0V, TA = TMIN to TMAX, unless otherwise noted.
Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SYNC Input High Pulse Width
Not tested
200
ns
SYNC Input Low Pulse Width
Not tested
200
ns
SYNC Rise/Fall Time
Not tested
SYNC Input Frequency Range
Current-Sense Input Leakage Current
200
ns
350
kHz
10
µA
13
14
V
2.44
2.60
240
V+ = VL = 0V,
CSL3 = CSH3 = CSL5 = CSH5 = 5.5V
0.01
FLYBACK CONTROLLER
VDD Regulation Threshold
Falling edge (Note 3)
SECFB Regulation Threshold
Falling edge (MAX1631/MAX1634)
DL Pulse Width
VDD < 13V or SECFB < 2.44V
VDD Shunt Threshold
Rising edge, hysteresis = 1% (Note 3)
18
VDD Shunt Sink Current
VDD = 20V (Note 3)
10
VDD Leakage Current
VDD = 5V, off mode (Notes 3, 4)
1
V
µs
20
V
mA
30
µA
12V LINEAR REGULATOR (Note 3)
12OUT Output Voltage
13V < VDD < 18V, 0mA < ILOAD < 120mA
12OUT Current Limit
12OUT forced to 11V, VDD = 13V
11.65
12.1
150
Quiescent VDD Current
VDD = 18V, run mode, no 12OUT load
50
12.50
V
mA
100
µA
5.1
V
INTERNAL REGULATOR AND REFERENCE
VL Output Voltage
SHDN = V+, RUN/ON3 = TIME/ON5 = 0V,
5.3V < V+ < 30V, 0mA < ILOAD < 50mA
4.7
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
No external load (Note 5)
2.45
2.5
2.55
V
REF Output Voltage
REF Load Regulation
0µA < ILOAD < 50µA
12.5
0mA < ILOAD < 5mA
100.0
REF Sink Current
10
mV
µA
REF Fault Lockout Voltage
Falling edge
2.4
V
V+ Operating Supply Current
VL switched over to CSL5, 5V SMPS on
1.8
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
200
µA
V+ Shutdown Supply Current
V+ = 4V to 24V, SHDN = 0V
4
10
µA
Both SMPSs enabled, FB3 = FB5 = 0V, (Note 3)
CSL3 = CSH3 = 3.5V,
MAX1631/
CSL5 = CSH5 = 5.3V
MAX1634
2.5
4
Quiescent Power Consumption
1.5
4
mW
_______________________________________________________________________________________
3
MAX1630–MAX1635
ELECTRICAL CHARACTERISTICS (continued)
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(V+ = 15V, both PWMs on, SYNC = VL, VL load = 0mA, REF load = 0mA, SKIP = 0V, TA = TMIN to TMAX, unless otherwise noted.
Typical values are at TA = +25°C.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
7
10
UNITS
FAULT DETECTION (MAX1630/MAX1631/MAX1632)
Overvoltage Trip Threshold
With respect to unloaded output voltage
Overvoltage-Fault Propagation Delay
CSL_ driven 2% above overvoltage trip threshold
Output Undervoltage Threshold
With respect to unloaded output voltage
Output Undervoltage Lockout Time
From each SMPS enabled, with respect to fOSC
Thermal Shutdown Threshold
Typical hysteresis = +10°C
4
1.5
%
µs
60
70
80
%
5000
6144
7000
Clk
150
°C
RESET
RESET Trip Threshold
With respect to unloaded output voltage,
falling edge; typical hysteresis = 1%
RESET Propagation Delay
Falling edge, CSL_ driven 2%
below RESET trip threshold
RESET Delay Time
With respect to fOSC
-7
-5.5
-4
1.5
27,000
%
µs
32,000
37,000
Clk
1
50
nA
0.6
V
INPUTS AND OUTPUTS
Feedback Input Leakage Current
FB3, FB5; SECFB = 2.6V
Logic Input Low Voltage
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC
Logic Input High Voltage
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC
Input Leakage Current
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC, SEQ; VPIN = 0V or 3.3V
±1
µA
Logic Output Low Voltage
RESET, ISINK = 4mA
0.4
V
Logic Output High Current
RESET = 3.5V
TIME/ON5 Input Trip Level
SEQ = 0V or VL
2.4
TIME/ON5 Source Current
TIME/ON5 = 0V, SEQ = 0V or VL
2.5
TIME/ON5 On-Resistance
Gate Driver Sink/Source Current
Gate Driver On-Resistance
High or low
2.4
V
1
mA
2.6
V
3
3.5
µA
TIME/ON5; RUN/ON3 = 0V, SEQ = 0V or VL
15
80
Ω
DL3, DH3, DL5, DH5; forced to 2V
1
7
Ω
1.5
A
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 Overload and Dropout Operation section).
Note 3: MAX1630/MAX1632/MAX1633/MAX1635 only.
Note 4: Off mode for the 12V linear regulator occurs when the SMPS that has flyback feedback (VDD) 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 VDD.
Note 5: Since the reference uses VL as its supply, the reference’s V+ line-regulation error is insignificant.
4
_______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
EFFICIENCY vs. 3.3V OUTPUT CURRENT
90
V+ = 15V
EFFICIENCY (%)
80
70
ON5 = 5V
ON3 = 0V
f = 300kHz
MAX1631/MAX1634
60
70
ON3 = ON5 = 5V
f = 300kHz
MAX1631/MAX1634
0.01
0.1
1
0.001
10
600
5V LOAD = 0A
400
5V LOAD = 3A
200
0.01
0.1
1
0
10
5
15
10
20
5V OUTPUT CURRENT (A)
3.3V OUTPUT CURRENT (A)
SUPPLY VOLTAGE (V)
MAX1630/MAX1633
MAXIMUM 15V VDD OUTPUT
CURRENT vs. SUPPLY VOLTAGE
PWM MODE INPUT CURRENT
vs. INPUT VOLTAGE
IDLE MODE INPUT CURRENT
vs. INPUT VOLTAGE
25
INPUT CURRENT (mA)
400
3.3V LOAD = 0A
300
200
3.3V LOAD = 3A
100
ON3 = ON5 = 5V
SKIP = VL
NO LOAD
10
ON3 = ON5 = 5V
SKIP = 0V
NO LOAD
INPUT CURRENT (mA)
VDD > 13V
3.3V REGULATING
MAX1630/35-05
30
MAX 1630/35-04
500
20
15
10
0
0
5
15
10
1
0.1
5
0
0.01
0
20
5
10
15
20
25
30
0
5
10
15
20
25
30
SUPPLY VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
STANDBY INPUT CURRENT
vs. INPUT VOLTAGE
SHUTDOWN INPUT CURRENT
vs. INPUT VOLTAGE
MINIMUM VIN TO VOUT DIFFERENTIAL
vs. 5V OUTPUT CURRENT
8
INPUT CURRENT (μA)
1000
SHDN = 0V
100
10
6
4
2
0
1
5
10
15
20
INPUT VOLTAGE (V)
25
30
1000
MAX1630/35-09
10
MIN VIN TO VOUT DIFFERENTIAL (mV)
ON3 = ON5 = 0V
NO LOAD
MAX1630/35-07
10,000
0
VDD > 13V
5V REGULATING
0
50
0.001
MAXIMUM OUTPUT CURRENT (mA)
V+ = 15V
60
50
INPUT CURRENT (μA)
80
MAX1630/35-08
EFFICIENCY (%)
90
800
MAX 1630/35-03
V+ = 6V
MAX1630/35-06
V+ = 6V
MAX1630/35-02
MAX1630/35-01
100
MAXIMUM OUTPUT CURRENT (mA)
EFFICIENCY vs. 5V OUTPUT CURRENT
100
MAX1632/MAX1635
MAXIMUM 15V VDD OUTPUT
CURRENT vs. SUPPLY VOLTAGE
100
10
5V, 3A CIRCUIT
VOUT > 4.8V
f = 300kHz
1
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
0.001
0.01
0.1
1
10
5V OUTPUT CURRENT (A)
_______________________________________________________________________________________
5
MAX1630–MAX1635
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, 3A Table 1 components, TA = +25°C, unless otherwise noted.)
____________________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, 3A Table 1 components, TA = +25°C, unless otherwise noted.)
VL REGULATOR OUTPUT VOLTAGE
vs. OUTPUT CURRENT
SWITCHING FREQUENCY
vs. LOAD CURRENT
VL OUTPUT VOLTAGE (V)
100
+5V, VIN = 15V
10
+3.3V, VIN = 15V
+3.3V, VIN = 6V
1
MAX 1630/35-11
5.00
MAX1630/35-10
SWITCHING FREQUENCY (kHz)
1000
4.98
4.96
4.94
4.92
VIN = 15V
ON3 = ON5 = 0V
+5V, VIN = 6V
4.90
0.1
10
1
100
0
1000
10
20
30
40
50
LOAD CURRENT (mA)
OUTPUT CURRENT (mA)
REF OUTPUT VOLTAGE
vs. OUTPUT CURRENT
START-UP WAVEFORMS
MAX 1630/35-12
2.510
2.505
2.500
60
MAX1630/35-13
0.1
REF OUTPUT VOLTAGE (V)
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
RUN
5V/div
3.3V OUTPUT
2V/div
2.495
TIME
5V/div
2.490
2.485
5V OUTPUT
5V/div
VIN = 15V
ON3 = ON5 = 0V
2.480
0
1
2
3
4
5
2ms/div
6
SEQ = VL, 0.015μF CAPACITOR ON-TIME
OUTPUT CURRENT (mA)
__________________________________________________________________________Pin Description
PIN
NAME
1
CSH3
Current-Sense Input for the 3.3V SMPS. Current-limit level is 100mV referred to CSL3.
2
CSL3
Current-Sense Input. Also serves as the feedback input in fixed-output mode.
3
FB3
Feedback Input for the 3.3V SMPS; regulates at FB3 = REF (approx. 2.5V) in adjustable mode. FB3 is a
Dual Mode input that also selects the 3.3V fixed output voltage setting when tied to GND. Connect FB3
to a resistor divider for adjustable-output mode.
12OUT
(MAX1630/
32/33/35)
12V/120mA Linear Regulator Output. Input supply comes from VDD. Bypass 12OUT to GND with
1µF minimum.
STEER
(MAX1631/
MAX1634)
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 = VL: 5V SMPS uses transformer
4
6
FUNCTION
_______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
PIN
NAME
FUNCTION
VDD
(MAX1630/
32/33/35)
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.
SECFB
(MAX1631/
MAX1634)
Secondary Winding Feedback Input. Normally connected to a resistor divider from an auxiliary output.
SECFB regulates at VSECFB = 2.5V (see Secondary Feedback Regulation Loop section). Tie to VL if not
used.
6
SYNC
Oscillator Synchronization and Frequency Select. Tie to VL for 300kHz operation; tie to GND for 200kHz
operation. Can be driven at 240kHz to 350kHz for external synchronization.
7
TIME/ON5
8
9
10
GND
REF
11
RESET
Active-Low Timed Reset Output. RESET swings GND to VL. Goes high after a fixed 32,000 clock-cycle
delay following power-up.
12
FB5
Feedback Input for the 5V SMPS; regulates at FB5 = REF (approx. 2.5V) in adjustable mode. FB5 is a
Dual Mode input that also selects the 5V fixed output voltage setting when tied to GND. Connect FB5 to
a resistor divider for adjustable-output mode.
13
CSL5
14
CSH5
15
SEQ
16
DH5
17
18
19
20
LX5
BST5
DL5
PGND
21
VL
5V Internal Linear-Regulator Output. VL is also the supply voltage rail for the chip. After the 5V SMPS
output has reached +4.5V (typical), VL automatically switches to the output voltage via CSL5 for bootstrapping. Bypass to GND with 4.7µF. VL supplies up to 25mA for external loads.
22
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 VL.
23
SHDN
24
25
26
DL3
BST3
LX3
27
DH3
28
RUN/ON3
5
SKIP
Dual-Purpose Timing Capacitor Pin and ON/OFF Control Input. See Power-Up Sequencing and
ON/OFF Controls section.
Low-Noise Analog Ground and Feedback Reference Point
2.5V Reference Voltage Output. Bypass to GND with 1µF minimum.
Logic-Control Input that disables Idle Mode when high. Connect to GND for normal use.
Current-Sense Input for the 5V SMPS. Also serves as the feedback input in fixed-output mode, and as
the bootstrap supply input when the voltage on CSL5/VL is > 4.5V.
Current-Sense Input for the 5V SMPS. Current-limit level is 100mV referred to CSL5.
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 = VL: 3.3V before 5V, RESET output determined by both outputs
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.
Switching Node (inductor) Connection. Can swing 2V below ground without hazard.
Boost capacitor connection for high-side gate drive (0.1µF)
Gate-Drive Output for the low-side synchronous-rectifier MOSFET. Swings 0V to VL.
Power Ground
Shutdown Control Input, active low. Logic threshold is set at approximately 1V. For automatic start-up,
connect SHDN to V+ through a 220kΩ resistor and bypass SHDN to GND with a 0.01µF capacitor.
Gate-Drive Output for the low-side synchronous-rectifier MOSFET. Swings 0V to VL.
Boost Capacitor Connection for high-side gate drive (0.1µF)
Switching Node (inductor) Connection. Can swing 2V below ground without hazard.
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.
ON/OFF Control Input. See Power-Up Sequencing and ON/OFF Controls section.
_______________________________________________________________________________________
7
MAX1630–MAX1635
_________________________________________________Pin Description (continued)
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
ON/OFF
INPUT
+5V ALWAYS ON
C3
10Ω
4.7μF
0.1μF
0.1μF
V+ SHDN SECFB VL
4.7μF
Q1
0.1μF
R1
+5V OUTPUT
C1
BST3
DH5
L1
Q3
DH3
0.1μF
0.1μF
Q2
*
SYNC
BST5
LX5
LX3
DL5
MAX1631
MAX1634 DL3
0.1μF
L2
R2
+3.3V OUTPUT
*
C2
Q4
PGND
CSH5
CSH3
CSL5
CSL3
FB3
FB5
RESET
5V ON/OFF
TIME/ON5
3.3V ON/OFF
RUN/ON3
RESET OUTPUT
SKIP
STEER
GND
SEQ
REF
+2.5V ALWAYS ON
1μF
*1A SCHOTTKY DIODE REQUIRED
FOR THE MAX1631 (SEE OUTPUT
OVERVOLTAGE PROTECTION SECTION).
Figure 1. Standard 3.3V/5V Application Circuit (MAX1631/MAX1634)
_______Standard Application Circuit
The basic MAX1631/MAX1634 dual-output 3.3V/5V
buck converter (Figure 1) is easily adapted to meet a
wide range of applications with inputs up to 28V by
substituting components from Table 1. These circuits
represent a good set of tradeoffs between cost, size,
and efficiency, while staying within the worst-case
specification limits for stress-related parameters, such
as capacitor ripple current. Don’t change the frequency
8
of these circuits without first recalculating component
values (particularly inductance value at maximum battery voltage). Adding a Schottky rectifier across each
synchronous rectifier improves the efficiency of these
circuits by approximately 1%, but this rectifier is otherwise not needed because the MOSFETs required for
these circuits typically incorporate a high-speed silicon
diode from drain to source. Use a Schottky rectifier
rated at a DC current equal to at least one-third of the
load current.
_______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
LOAD CURRENT
COMPONENT
2A
3A
4A
Input Range
4.75V to 18V
4.75V to 28V
4.75V to 24V
Application
PDA
Notebook
Workstation
Frequency
300kHz
300kHz
200kHz
Q1, Q3 High-Side
MOSFETs
1/2 IR IRF7301;
1/2 Siliconix Si9925DQ; or
1/2 Motorola MMDF3N03HD or
MMDF4N01HD (10V max)
IR IRF7403 or IRF7401 (18V
max); Siliconix Si4412DY; or
Motorola MMSF5N03HD or
MMSF5N02HD (18V max)
IR IRF7413 or
Siliconix Si4410DY
Q2, Q4 Low-Side
MOSFETs
1/2 IR IRF7301;
1/2 Siliconix Si9925DQ; or
1/2 Motorola MMDF3N03HD or
MMDF4N01HD (10V max)
IR IRF7403 or IRF7401 (18V
max); Siliconix Si4412DY; or
Motorola MMSF5N03HD or
MMSF5N02HD (18V max)
IR IRF7413 or
Siliconix Si4410DY
C3 Input Capacitor
10µF, 30V Sanyo OS-CON;
22µF, 35V AVX TPS; or
Sprague 594D
2 x 10µF, 30V Sanyo OS-CON;
2 x 22µF, 35V AVX TPS; or
Sprague 594D
3 x 10µF, 30V Sanyo OS-CON;
4 x 22µF, 35V AVX TPS; or
Sprague 595D
C1, C2 Output Capacitors
220µF, 10V AVX TPS or
Sprague 595D
2 x 220µF, 10V AVX TPS or
Sprague 595D
4 x 220µF, 10V AVX TPS or
Sprague 595D
R1, R2 Resistors
0.033Ω IRC LR2010-01-R033 or
Dale WSL2010-R033-F
0.02Ω IRC LR2010-01-R020 or
Dale WSL2010-R020-F
0.012Ω Dale WSL2512-R012-F
15µH, 2.4A Ferrite
Coilcraft DO3316P-153 or
Sumida CDRH125-150
10µH, 4A Ferrite
Coilcraft DO3316P-103 or
Sumida CDRH125-100
4.7µH, 5.5A Ferrite
Coilcraft DO3316-472 or
5.2µH, 6.5A Ferrite Sumida
CDRH127-5R2MC
L1, L2 Inductors
Table 2. Component Suppliers
COMPANY
AVX
FACTORY FAX
(COUNTRY CODE)
(1) 803-626-3123
USA PHONE
(803) 946-0690
COMPANY
FACTORY FAX
(COUNTRY CODE)
USA PHONE
Motorola
(1) 602-994-6430
(602) 303-5454
Murata-Erie
(1) 814-238-0490
(814) 237-1431
NIEC
(81) 3-3494-7414
(805) 867-2555*
Central
Semiconductor
(1) 516-435-1824
(516) 435-1110
Coilcraft
(1) 847-639-1469
(847) 639-6400
Sanyo
(81) 7-2070-1174
(619) 661-6835
Coiltronics
(1) 561-241-9339
(561) 241-7876
Siliconix
(1) 408-970-3950
(408) 988-8000
Dale
(1) 605-665-1627
(605) 668-4131
Sprague
(1) 603-224-1430
(603) 224-1961
Sumida
(81) 3-3607-5144
(847) 956-0666
TDK
(1) 847-390-4428
(847) 390-4373
Transpower
Technologies
(1) 702-831-3521
(702) 831-0140
International
Rectifier (IR)
(1) 310-322-3332
(310) 322-3331
IRC
(1) 512-992-3377
(512) 992-7900
Matsuo
(1) 714-960-6492
(714) 969-2491
*Distributor
_______________________________________________________________________________________
9
MAX1630–MAX1635
Table 1. Component Selection for Standard 3.3V/5V Application
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
INPUT
V+
SHDN
SYNC
CSL5
+
MAX1632
4.5V
ON/OFF
+5V ALWAYS ON
12V
LINEAR
REG
5V
LINEAR
REG
VL
REF
VDD
+
-
13V
DH3
+3.3V
+12V
IN
SECFB
2.5V
REF
BST3
12OUT
BST5
RAW +15V
DH5
LX3
VL
DL3
3.3V
PWM
LOGIC
5V
PWM
LOGIC
200kHz
TO
300kHz
OSC
LX5
+5V
VL
DL5
PGND
OV/UV
FAULT
+
CSL3
REF
-
REF
LPF
60kHz
+
LPF
60kHz
1.75V
2.68V
CSH5
CSL5
-
CSH3
2.388V
FB3
-
R3
FB5
OUTPUTS
UP
-
-
R2
-
+
+
R1
+
R4
+
0.6V
0.6V
VL
REF
-
POWER-ON
SEQUENCE
LOGIC
+
SEQ
+
+
1V
RUN/ON3
RESET
2.6V
-
TIME/ON5
TIMER
GND
Figure 2. MAX1632 Block Diagram
10
______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
The MAX1630 is a dual, BiCMOS, switch-mode powersupply controller designed primarily for buck-topology
regulators in battery-powered applications where high efficiency and low quiescent supply current are critical. Lightload efficiency is enhanced by automatic Idle Mode™
operation, a variable-frequency pulse-skipping mode that
reduces transition and gate-charge losses. Each stepdown, power-switching circuit consists of two N-channel
MOSFETs, a rectifier, and an LC output filter. The output
voltage is the average AC voltage at the switching node,
which is regulated by changing the duty cycle of the
MOSFET switches. The gate-drive signal to the N-channel
high-side MOSFET must exceed the battery voltage, and
is provided by a flying-capacitor boost circuit that uses a
100nF capacitor connected to BST_.
Devices in the MAX1630 family contain ten major circuit
blocks (Figure 2).
The two pulse-width modulation (PWM) controllers each
consist of a Dual Mode™ feedback network and multiplexer, a multi-input PWM comparator, high-side and
low-side gate drivers, and logic. MAX1630/MAX1631/
MAX1632 contain fault-protection circuits that monitor
the main PWM outputs for undervoltage and overvoltage. A power-on sequence block controls the powerup timing of the main PWMs and determines whether
one or both of the outputs are monitored for undervoltage faults. The MAX1630/MAX1632/MAX1633/
MAX1635 include a secondary feedback network and
12V linear regulator to generate a 12V output from a
coupled-inductor flyback winding. The MAX1631/
MAX1634 have a secondary feedback input (SECFB)
instead, which allows a quasi-regulated, adjustableoutput, coupled-inductor flyback winding to be attached
to either the 3.3V or the 5V main inductor. Bias generator blocks include the 5V IC internal rail (VL) linear regulator, 2.5V precision reference, and automatic bootstrap
switchover circuit. The PWMs share a common
200kHz/300kHz synchronizable oscillator.
These internal IC blocks aren’t powered directly from
the battery. Instead, the 5V VL linear regulator steps
down the battery voltage to supply both VL and the
gate drivers. The synchronous-switch gate drivers are
directly powered from VL, while the high-side switch
gate drivers are indirectly powered from VL via an
external diode-capacitor boost circuit. An automatic
bootstrap circuit turns off the +5V linear regulator and
powers the IC from the 5V PWM output voltage if the
output is above 4.5V.
PWM Controller Block
The two PWM controllers are nearly identical. The only
differences are fixed output settings (3.3V vs. 5V), the
VL/CSL5 bootstrap switch connected to the +5V PWM,
and SECFB. The heart of each current-mode PWM controller is a multi-input, open-loop comparator that sums
three signals: the output voltage error signal with
respect to the reference voltage, the current-sense signal, and the slope compensation ramp (Figure 3). The
PWM controller is a direct-summing type, lacking a traditional error amplifier and the phase shift associated
with it. This direct-summing configuration approaches
ideal cycle-by-cycle control over the output voltage.
When SKIP = low, Idle Mode circuitry automatically
optimizes efficiency throughout the load current range.
Idle Mode dramatically improves light-load efficiency
by reducing the effective frequency, which reduces
switching losses. It keeps the peak inductor current
above 25% of the full current limit in an active cycle,
allowing subsequent cycles to be skipped. Idle Mode
transitions seamlessly to fixed-frequency PWM operation as load current increases.
With SKIP = high, the controller always operates in
fixed-frequency PWM mode for lowest noise. Each
pulse from the oscillator sets the main PWM latch that
turns on the high-side switch for a period determined
by the duty factor (approximately V OUT/VIN). As the
high-side switch turns off, the synchronous rectifier
latch sets; 60ns later, the low-side switch turns on. The
low-side switch stays on until the beginning of the next
clock cycle.
Table 3. SKIP PWM Table
SKIP
LOAD
CURRENT
MODE
DESCRIPTION
Low
Light
Idle
Pulse-skipping, supply current = 250µA at VIN = 12V,
discontinuous inductor
current
Low
Heavy
PWM
Constant-frequency PWM,
continuous inductor current
High
Light
PWM
Constant-frequency PWM,
continuous inductor current
High
Heavy
PWM
Constant-frequency PWM,
continuous inductor current
______________________________________________________________________________________
11
MAX1630–MAX1635
_______________Detailed Description
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
CSH_
1X
CSL_
REF
FROM
FEEDBACK
DIVIDER
MAIN PWM
COMPARATOR
BST_
R
LEVEL
SHIFT
Q
S
DH_
LX_
SLOPE COMP
OSC
30mV
SKIP
CURRENT
LIMIT
DAC
SHOOTTHROUGH
CONTROL
CK
COUNTER
SHDN
SOFT-START
SYNCHRONOUS
RECTIFIER CONTROL
R
-100mV
S
VL
Q
LEVEL
SHIFT
DL_
PGND
REF
1μs
SINGLE-SHOT
SECFB
Figure 3. PWM Controller Detailed Block Diagram
12
______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
The output filter capacitors (Figure 1, C1 and C2) set a
dominant pole in the feedback loop that must roll off the
loop gain to unity before encountering the zero introduced by the output capacitor’s parasitic resistance
(ESR) (see Design Procedure section). A 60kHz polezero cancellation filter provides additional rolloff above
the unity-gain crossover. This internal 60kHz lowpass
compensation filter cancels the zero due to filter capacitor ESR. The 60kHz filter is included in the loop in both
fixed-output and adjustable-output modes.
Synchronous Rectifier Driver (DL)
Synchronous rectification reduces conduction losses in
the rectifier by shunting the normal Schottky catch diode
with a low-resistance MOSFET switch. Also, the synchronous rectifier ensures proper start-up of the boost gatedriver circuit. If the synchronous power MOSFETs are
omitted for cost or other reasons, replace them with a
small-signal MOSFET, such as a 2N7002.
If the circuit is operating in continuous-conduction
mode, the DL drive waveform is simply the complement
of the DH high-side drive waveform (with controlled
dead time to prevent cross-conduction or “shootthrough”). In discontinuous (light-load) mode, the synchronous switch is turned off as the inductor current
falls through zero. The synchronous rectifier works
The MAX1630 family uses a relatively low loop gain,
allowing the use of lower-cost output capacitors. The
relative gains of the voltage-sense and current-sense
inputs are weighted by the values of current sources
that bias three differential input stages in the main PWM
comparator (Figure 4). The relative gain of the voltage
comparator to the current comparator is internally fixed
at K = 2:1. The low loop gain results in the 2% typical
load-regulation error. The low value of loop gain helps
reduce output filter capacitor size and cost by shifting
the unity-gain crossover frequency to a lower level.
VL
R1
R2
TO PWM
LOGIC
UNCOMPENSATED
HIGH-SPEED
LEVEL TRANSLATOR
AND BUFFER
OUTPUT DRIVER
FB_
I1
I2
I3
VBIAS
REF
CSH_
CSL_
SLOPE COMPENSATION
Figure 4. Main PWM Comparator Block Diagram
______________________________________________________________________________________
13
MAX1630–MAX1635
In PWM mode, the controller operates as a fixedfrequency current-mode controller where the duty ratio
is set by the input/output voltage ratio. The currentmode feedback system regulates the peak inductor
current value as a function of the output-voltage error
signal. In continuous-conduction mode, the average
inductor current is nearly the same as the peak current,
so the circuit acts as a switch-mode transconductance
amplifier. This pushes the second output LC filter pole,
normally found in a duty-factor-controlled (voltagemode) PWM, to a higher frequency. To preserve innerloop stability and eliminate regenerative inductor
current “staircasing,” a slope compensation ramp is
summed into the main PWM comparator to make the
apparent duty factor less than 50%.
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
under all operating conditions, including Idle Mode.
The SECFB signal further controls the synchronous
switch timing in order to improve multiple-output crossregulation (see Secondary Feedback Regulation Loop
section).
Internal VL and REF Supplies
An internal regulator produces the +5V supply (VL) that
powers the PWM controller, logic, reference, and other
blocks within the IC. This 5V low-dropout linear regulator supplies up to 25mA for external loads, with a
reserve of 25mA for supplying gate-drive power.
Bypass VL to GND with 4.7µF.
Important: Ensure that VL does not exceed 6V.
Measure VL with the main output fully loaded. If it is
pumped above 5.5V, either excessive boost diode
capacitance or excessive ripple at V+ is the probable
cause. Use only small-signal diodes for the boost circuit (10mA to 100mA Schottky or 1N4148 are preferred), and bypass V+ to PGND with 4.7µF directly at
the package pins.
The 2.5V reference (REF) is accurate to ±2% over temperature, making REF useful as a precision system reference. Bypass REF to GND with 1µF minimum. REF
can supply up to 5mA for external loads. (Bypass REF
with a minimum 1µF/mA reference load current.)
However, if extremely accurate specifications for both
the main output voltages and REF are essential, avoid
loading REF more than 100µA. Loading REF reduces
the main output voltage slightly, because of the reference load-regulation error.
When the 5V main output voltage is above 4.5V, an
internal P-channel MOSFET switch connects CSL5 to
VL, while simultaneously shutting down the VL linear
regulator. This action bootstraps the IC, powering the
internal circuitry from the output voltage, rather than
through a linear regulator from the battery.
Bootstrapping reduces power dissipation due to gate
charge and quiescent losses by providing that power
from a 90%-efficient switch-mode source, rather than
from a much less efficient linear regulator.
Boost High-Side Gate-Drive Supply
(BST3 and BST5)
Gate-drive voltage for the high-side N-channel switches
is generated by a flying-capacitor boost circuit
(Figure 2). The capacitor between BST_ and LX_ is
alternately charged from the VL supply and placed parallel to the high-side MOSFET’s gate-source terminals.
On start-up, the synchronous rectifier (low-side
MOSFET) forces LX_ to 0V and charges the boost
capacitors to 5V. On the second half-cycle, the SMPS
14
turns on the high-side MOSFET by closing an internal
switch between BST_ and DH_. This provides the necessary enhancement voltage to turn on the high-side
switch, an action that “boosts” the 5V gate-drive signal
above the battery voltage.
Ringing at the high-side MOSFET gate (DH3 and DH5)
in discontinuous-conduction mode (light loads) is a natural operating condition. It is caused by residual energy in the tank circuit, formed by the inductor and stray
capacitance at the switching node, LX. The gate-drive
negative rail is referred to LX, so any ringing there is
directly coupled to the gate-drive output.
Current-Limiting and Current-Sense
Inputs (CSH and CSL)
The current-limit circuit resets the main PWM latch and
turns off the high-side MOSFET switch whenever the
voltage difference between CSH and CSL exceeds
100mV. This limiting is effective for both current flow
directions, putting the threshold limit at ±100mV. The
tolerance on the positive current limit is ±20%, so the
external low-value sense resistor (R1) must be sized for
80mV/IPEAK, where IPEAK is the required peak inductor
current to support the full load current, while components must be designed to withstand continuous current stresses of 120mV/R1.
For breadboarding or for very-high-current applications,
it may be useful to wire the current-sense inputs with a
twisted pair, rather than PC traces. (This twisted pair
needn’t be anything special; two pieces of wire-wrap
wire twisted together are sufficient.) This reduces the
possible noise picked up at CSH_ and CSL_, which can
cause unstable switching and reduced output current.
The CSL5 input also serves as the IC’s bootstrap supply input. Whenever VCSL5 > 4.5V, an internal switch
connects CSL5 to VL.
Oscillator Frequency and
Synchronization (SYNC)
The SYNC input controls the oscillator frequency. Low
selects 200kHz; high selects 300kHz. SYNC can also
be used to synchronize with an external 5V CMOS or
TTL clock generator. SYNC has a guaranteed 240kHz
to 350kHz capture range. A high-to-low transition on
SYNC initiates a new cycle.
300kHz operation optimizes the application circuit for
component size and cost. 200kHz operation provides
increased efficiency, lower dropout, and improved
load-transient response at low input-output voltage differences (see Low-Voltage Operation section).
______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Power-Up Sequencing
and ON/OFF Controls
Start-up is controlled by RUN/ON3 and TIME/ON5 in
conjunction with SEQ. With SEQ tied to REF, the two
control inputs act as separate ON/OFF controls for
each supply. With SEQ tied to VL or GND, RUN/ON3
becomes the master ON/OFF control input and
TIME/ON5 becomes a timing pin, with the delay
between the two supplies determined by an external
capacitor. The delay is approximately 800µs/nF. The
+3.3V supply powers-up first if SEQ is tied to VL, and
the +5V supply is first if SEQ is tied to GND. When driving TIME/ON5 as a control input with external logic,
always place a resistor (>1kΩ) in series with the input.
This prevents possible crowbar current due to the internal discharge pull-down transistor, which turns on in
standby mode and momentarily at the first power-up or
in shutdown mode.
RESET Power-Good Voltage Monitor
The power-good monitor generates a system RESET signal. At first power-up, RESET is held low until both the
3.3V and 5V SMPS outputs are in regulation. At this point,
an internal timer begins counting oscillator pulses, and
RESET continues to be held low until 32,000 cycles have
elapsed. After this timeout period (107ms at 300kHz or
160ms at 200kHz), RESET is actively pulled up to VL. If
SEQ is tied to REF (for separate ON3/ON5 controls), only
the 3.3V SMPS is monitored—the 5V SMPS is ignored.
Output Undervoltage Shutdown Protection
(MAX1630/MAX1631/MAX1632)
The output undervoltage lockout circuit is similar to
foldback current limiting, but employs a timer rather
than a variable current limit. Each SMPS has an undervoltage protection circuit that is activated 6144 clock
cycles after the SMPS is enabled. If either SMPS output
is under 70% of the nominal value, both SMPSs are
latched off and their outputs are clamped to ground by
the synchronous rectifier MOSFETs (see Output
Overvoltage Protection section). They won’t restart until
SHDN or RUN/ON3 is toggled, or until V+ power is
cycled below 1V. Note that undervoltage protection can
make prototype troubleshooting difficult, since you
have only 20ms or 30ms to figure out what might be
wrong with the circuit before both SMPSs are latched
off. In extreme cases, it may be useful to substitute the
MAX1633/MAX1634/MAX1635 into the prototype
breadboard until the prototype is working properly.
Output Overvoltage Protection
(MAX1630/MAX1631/MAX1632)
Both SMPS outputs are monitored for overvoltage. If
either output is more than 7% above the nominal regulation point, both low-side gate drivers (DL_) are
latched high until SHDN or RUN/ON3 is toggled, or until
V+ power is cycled below 1V. This action turns on the
synchronous rectifiers with 100% duty, in turn rapidly
discharging the output capacitors and forcing both
SMPS outputs to ground. The DL outputs are also kept
high whenever the corresponding SMPS is disabled,
and in shutdown if VL is sustained.
Table 4. Operating Modes
SHDN
SEQ
RUN/ON3
TIME/ON5
MODE
DESCRIPTION
All circuit blocks turned off. Supply current = 4µA.
Low
X
X
X
Shutdown
High
Ref
Low
Low
Standby
High
Ref
High
Low
Run
3.3V SMPS enabled/5V off
High
Ref
Low
High
Run
5V SMPS enabled/3.3V off
High
Ref
High
High
Run
Both SMPSs enabled
High
GND
Low
Timing capacitor
Standby
High
GND
High
Timing capacitor
Run
High
VL
Low
Timing capacitor
Standby
High
VL
High
Timing capacitor
Run
Both SMPSs off. Supply current = 30µA.
Both SMPSs off. Supply current = 30µA.
Both SMPSs enabled. 5V enabled before 3.3V.
Both SMPSs off. Supply current = 30µA.
Both SMPSs enabled. 3.3V enabled before 5V.
X = Don’t Care
______________________________________________________________________________________
15
MAX1630–MAX1635
Shutdown Mode
Holding SHDN low puts the IC into its 4µA shutdown
mode. SHDN is logic input with a threshold of about 1V
(the VTH of an internal N-channel MOSFET). For automatic start-up, bypass SHDN to GND with a 0.01µF
capacitor and connect it to V+ through a 220kΩ resistor.
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Discharging the output capacitor through the main
inductor causes the output to momentarily go below
GND. Clamp this negative pulse with a back-biased 1A
Schottky diode across the output capacitor (Figure 1).
To ensure overvoltage protection on initial power-up,
connect signal diodes from both output voltages to VL
(cathodes to VL) to eliminate the VL power-up delay.
This circuitry protects the load from accidental overvoltage caused by a short-circuit across the high-side
power MOSFETs. This scheme relies on the presence
of a fuse, in series with the battery, which is blown by
the resulting crowbar current. Note that the overvoltage
circuitry will interfere with external keep-alive supplies
that hold up the outputs (such as lithium backup or hotswap power supplies); in such cases, the MAX1633,
MAX1634, or MAX1635 should be used.
Low-Noise Operation (PWM Mode)
PWM mode (SKIP = high) minimizes RF and audio
interference in noise-sensitive applications (such as hifi multimedia-equipped systems), cellular phones, RF
communicating computers, and electromagnetic penentry systems. See the summary of operating modes in
Table 2. SKIP can be driven from an external logic
signal.
Interference due to switching noise is reduced in PWM
mode by ensuring a constant switching frequency, thus
concentrating the emissions at a known frequency outside the system audio or IF bands. Choose an oscillator
frequency for which switching frequency harmonics
don’t overlap a sensitive frequency band. If necessary,
synchronize the oscillator to a tight-tolerance external
clock generator. To extend the output-voltage-regulation range, constant operating frequency is not maintained under overload or dropout conditions (see
Overload and Dropout Operation section.)
PWM mode (SKIP = high) forces two changes upon the
PWM controllers. First, it disables the minimum-current
comparator, ensuring fixed-frequency operation.
Second, it changes the detection threshold for reversecurrent limit from 0mV to -100mV, allowing the inductor
current to reverse at light loads. This results in fixedfrequency operation and continuous inductor-current
flow. This eliminates discontinuous-mode inductor ringing and improves cross regulation of transformercoupled multiple-output supplies, particularly in circuits
that don’t use additional secondary regulation via
SECFB or VDD.
In most applications, tie SKIP to GND to minimize quiescent supply current. VL supply current with SKIP high
is typically 20mA, depending on external MOSFET gate
capacitance and switching losses.
16
Internal Digital Soft-Start Circuit
Soft-start allows a gradual increase of the internal current-limit level at start-up to reduce input surge currents.
Both SMPSs contain internal digital soft-start circuits,
each controlled by a counter, a digital-to-analog converter (DAC), and a current-limit comparator. In shutdown or standby mode, the soft-start counter is reset to
zero. When an SMPS is enabled, its counter starts
counting oscillator pulses, and the DAC begins incrementing the comparison voltage applied to the currentlimit comparator. The DAC output increases from 0mV to
100mV in five equal steps as the count increases to 512
clocks. As a result, the main output capacitor charges
up relatively slowly. The exact time of the output rise
depends on output capacitance and load current, and
is typically 1ms with a 300kHz oscillator.
Dropout Operation
Dropout (low input-output differential operation) is
enhanced by stretching the clock pulse width to
increase the maximum duty factor. The algorithm follows: If the output voltage (VOUT) drops out of regulation without the current limit having been reached, the
SMPS skips an off-time period (extending the on-time).
At the end of the cycle, if the output is still out of regulation, the SMPS skips another off-time period. This
action can continue until three off-time periods are
skipped, effectively dividing the clock frequency by as
much as four.
The typical PWM minimum off-time is 300ns, regardless
of the operating frequency. Lowering the operating frequency raises the maximum duty factor above 98%.
Adjustable-Output Feedback
(Dual Mode FB)
Fixed, preset output voltages are selected when FB_ is
connected to ground. Adjusting the main output voltage with external resistors is simple for any of the
MAX1630 family ICs, through resistor dividers connected to FB3 and FB5 (Figure 2). Calculate the output voltage with the following formula:
VOUT = VREF (1 + R1 / R2)
where VREF = 2.5V nominal.
The nominal output should be set approximately 1% or
2% high to make up for the MAX1630’s -2% typical
load-regulation error. For example, if designing for a
3.0V output, use a resistor ratio that results in a nominal
output voltage of 3.05V. This slight offsetting gives the
best possible accuracy. Recommended normal values
for R2 range from 5kΩ to 100kΩ. To achieve a 2.5V
nominal output, simply connect FB_ directly to CSL_.
______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Secondary Feedback Regulation Loop
(SECFB or VDD)
A flyback-winding control loop regulates a secondary
winding output, improving cross-regulation when the
primary output is lightly loaded or when there is a low
input-output differential voltage. If VDD or SECFB falls
below its regulation threshold, the low-side switch is
turned on for an extra 1µs. This reverses the inductor
(primary) current, pulling current from the output filter
capacitor and causing the flyback transformer to operate in forward mode. The low impedance presented by
the transformer secondary in forward mode dumps current into the secondary output, charging up the secondary capacitor and bringing VDD or SECFB back into
regulation. The secondary feedback loop does not
improve secondary output accuracy in normal flyback
mode, where the main (primary) output is heavily
loaded. In this condition, secondary output accuracy is
determined by the secondary rectifier drop, transformer
turns ratio, and accuracy of the main output voltage. A
linear post-regulator may still be needed to meet strict
output-accuracy specifications.
Devices with a 12OUT linear regulator have a VDD pin
that regulates at a fixed 13.5V, set by an internal resistor divider. The MAX1631/MAX1634 have an adjustable
secondary output voltage set by an external resistor
divider on SECFB (Figure 5). Ordinarily, the secondary
regulation point is set 5% to 10% below the voltage normally produced by the flyback effect. For example, if
the output voltage as determined by turns ratio is 15V,
set the feedback resistor ratio to produce 13.5V.
Otherwise, the SECFB one-shot might be triggered
unintentionally, unnecessarily increasing supply current
and output noise.
R2
SECFB
1-SHOT
TRIG
R1
2.5V REF
POSITIVE
SECONDARY
OUTPUT
V+
DH_
MAIN
OUTPUT
MAX1631
MAX1634
DL_
R1
+VTRIP = VREF 1 + –––
R2
(
)
WHERE VREF (NOMINAL) = 2.5V
Figure 5. Adjusting the Secondary Output Voltage with SECFB
+12V OUTPUT
200mA
12OUT
0.1μF
10μF
VDD
2N3906
0.1μF
MAX1630
MAX1632
MAX1633
MAX1635 DH_
V+
10Ω
0.1μF
VDD OUTPUT
2.2μF
MAIN
OUTPUT
DL_
Figure 6. Increased 12V Linear Regulator Output Current
12V Linear Regulator Output
(MAX1630/MAX1632/MAX1633/MAX1635)
The MAX1630/MAX1632/MAX1633/MAX1635 include a
12V linear regulator output capable of delivering 120mA
of output current. Typically, greater current is available
at the expense of output accuracy. If an accurate output
of more than 120mA is needed, an external pass tran-
______________________________________________________________________________________
17
MAX1630–MAX1635
Remote output-voltage sensing, while not possible in
fixed-output mode due to the combined nature of the
voltage-sense and current-sense inputs (CSL3 and
CSL5), is easy to do in adjustable mode by using the top
of the external resistor divider as the remote sense point.
When using adjustable mode, it is a good idea to
always set the “3.3V output” to a lower voltage than the
“5V output.” The 3.3V output must always be less than
VL, so that the voltage on CSH3 and CSL3 is within the
common-mode range of the current-sense inputs. While
VL is nominally 5V, it can be as low as 4.7V when linearly regulating, and as low as 4.2V when automatically
bootstrapped to CSH5.
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
sistor can be added. Figure 6’s circuit delivers more
than 200mA. Total output current is constrained by the
V+ input voltage and the transformer primary load (see
Maximum 15V VDD Output Current vs. Supply Voltage
graphs in the Typical Operating Characteristics).
__________________Design Procedure
The three predesigned 3V/5V standard application circuits (Figure 1 and Table 1) contain ready-to-use solutions for common application needs. Also, two standard
flyback transformer circuits support the 12OUT linear
regulator in the Applications Information section. Use
the following design procedure to optimize these basic
schematics for different voltage or current requirements. But before beginning a design, firmly establish
the following:
Maximum input (battery) voltage, V IN(MAX) . This
value should include the worst-case conditions, such
as no-load operation when a battery charger or AC
adapter is connected but no battery is installed.
VIN(MAX) must not exceed 30V.
Minimum input (battery) voltage, V IN(MIN) . This
should be taken at full load under the lowest battery
conditions. If VIN(MIN) is less than 4.2V, use an external
circuit to externally hold VL above the VL undervoltage
lockout threshold. If the minimum input-output difference is less than 1.5V, the filter capacitance required to
maintain good AC load regulation increases (see LowVoltage Operation section).
Inductor Value
The exact inductor value isn’t critical and can be freely
adjusted to make trade-offs between size, cost, and
efficiency. Lower inductor values minimize size and
cost, but reduce efficiency due to higher peak-current
levels. The smallest inductor is achieved by lowering
the inductance until the circuit operates at the border
between continuous and discontinuous mode. Further
reducing the inductor value below this crossover point
results in discontinuous-conduction operation even at
full load. This helps lower output filter capacitance
requirements, but efficiency suffers due to high I 2R
losses. On the other hand, higher inductor values mean
greater efficiency, but resistive losses due to extra wire
turns will eventually exceed the benefit gained from
lower peak-current levels. Also, high inductor values
can affect load-transient response (see the VSAG equation in the Low-Voltage Operation section). The equations that follow are for continuous-conduction
operation, since the MAX1630 family is intended mainly
for high-efficiency, battery-powered applications. See
Appendix A in Maxim’s Battery Management and DCDC Converter Circuit Collection for crossover-point and
discontinuous-mode equations. Discontinuous conduction doesn’t affect normal Idle Mode operation.
Three key inductor parameters must be specified:
inductance value (L), peak current (IPEAK), and DC
resistance (R DC). The following equation includes a
constant, LIR, which is the ratio of inductor peak-topeak AC current to DC load current. A higher LIR value
allows smaller inductance, but results in higher losses
and higher ripple. A good compromise between size
and losses is found at a 30% ripple-current to loadcurrent ratio (LIR = 0.3), which corresponds to a peak
inductor current 1.15 times higher than the DC load
current.
L =
VOUT (VIN(MAX) - VOUT )
VIN(MAX) x f x IOUT x LIR
where: f = switching frequency, normally 200kHz or
300kHz
IOUT = maximum DC load current
LIR = ratio of AC to DC inductor current, typically 0.3; should be selected for >0.15
The nominal peak inductor current at full load is 1.15 x
IOUT if the above equation is used; otherwise, the peak
current can be calculated by:
IPEAK = ILOAD +
VOUT (VIN(MAX) - VOUT )
2 x f x L x VIN(MAX)
The inductor’s DC resistance should be low enough that
RDC x IPEAK < 100mV, as it is a key parameter for efficiency performance. If a standard off-the-shelf inductor
is not available, choose a core with an LI2 rating greater
than L x IPEAK2 and wind it with the largest-diameter
wire that fits the winding area. For 300kHz applications,
ferrite core material is strongly preferred; for 200kHz
applications, Kool-Mu® (aluminum alloy) or even powdered iron is acceptable. If light-load efficiency is unimportant (in desktop PC applications, for example), then
low-permeability iron-powder cores, such as the
Micrometals type found in Pulse Engineering’s 2.1µH
PE-53680, may be acceptable even at 300kHz. For
high-current applications, shielded-core geometries,
such as toroidal or pot core, help keep noise, EMI, and
switching-waveform jitter low.
Kool-Mu is a registered trademark of Magnetics Div., Spang & Co.
18
______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Bypassing VL
Bypass the VL output with a 4.7µF tantalum capacitor
paralleled with a 0.1µF ceramic capacitor, close to the
device.
80mV
RSENSE =
IPEAK
The output filter capacitor values are generally determined by the ESR and voltage rating requirements, rather
than actual capacitance requirements for loop stability. In
other words, the low-ESR electrolytic capacitor that meets
the ESR requirement usually has more output capacitance than is required for AC stability. Use only specialized low-ESR capacitors intended for switching-regulator
applications, such as AVX TPS, Sprague 595D, Sanyo
OS-CON, or Nichicon PL series. To ensure stability, the
capacitor must meet both minimum capacitance and
maximum ESR values as given in the following equations:
Use IPEAK from the second equation in the Inductor
Value section
Use the calculated value of RSENSE to size the MOSFET
switches and specify inductor saturation-current ratings
according to the worst-case high-current-limit threshold
voltage:
IPEAK(MAX) =
120mV
RSENSE
Low-inductance resistors, such as surface-mount
metal-film, are recommended.
Input Capacitor Value
Connect low-ESR bulk capacitors and small ceramic
capacitors (0.1µF) directly to the drains on the highside MOSFETs. The bulk input filter capacitor is usually
selected according to input ripple current requirements
and voltage rating, rather than capacitor value.
Electrolytic capacitors with low enough effective series
resistance (ESR) to meet the ripple current requirement
invariably have sufficient capacitance values.
Aluminum electrolytic capacitors, such as Sanyo
OS-CON or Nichicon PL, are superior to tantalum
types, which carry the risk of power-up surge-current
failure, especially when connecting to robust AC
adapters or low-impedance batteries. RMS input ripple
current (IRMS) is determined by the input voltage and
load current, with the worst case occurring at VIN = 2 x
VOUT:
IRMS = ILOAD x
VOUT (VIN - VOUT )
VIN
Therefore, when VIN is 2 x VOUT :
I
IRMS = LOAD
2
Bypassing V+
Bypass the V+ input with a 4.7µF tantalum capacitor
paralleled with a 0.1µF ceramic capacitor, close to the
IC. A 10Ω series resistor to VIN is also recommended.
Output Filter Capacitor Value
COUT >
VREF (1 + VOUT / VIN(MIN) )
VOUT x RSENSE x f
RESR <
RSENSE x VOUT
VREF
(can be multiplied by 1.5; see text below)
These equations are worst case, with 45 degrees of
phase margin to ensure jitter-free, fixed-frequency
operation and provide a nicely damped output
response for zero to full-load step changes. Some costconscious designers may wish to bend these rules with
less-expensive capacitors, particularly if the load lacks
large step changes. This practice is tolerable if some
bench testing over temperature is done to verify
acceptable noise and transient response.
No well-defined boundary exists between stable and
unstable operation. As phase margin is reduced, the
first symptom is a bit of timing jitter, which shows up as
blurred edges in the switching waveforms where the
scope won’t quite sync up. Technically speaking, this
jitter (usually harmless) is unstable operation, since the
duty factor varies slightly. As capacitors with higher
ESRs are used, the jitter becomes more pronounced,
and the load-transient output voltage waveform starts
looking ragged at the edges. Eventually, the load-transient waveform has enough ringing on it that the peak
noise levels exceed the allowable output voltage tolerance. Note that even with zero phase margin and gross
instability present, the output voltage noise never gets
much worse than IPEAK x RESR (under constant loads).
Designers of RF communicators or other noise-sensitive analog equipment should be conservative and stay
within the guidelines. Designers of notebook computers
and similar commercial-temperature-range digital
______________________________________________________________________________________
19
MAX1630–MAX1635
Current-Sense Resistor Value
The current-sense resistor value is calculated according
to the worst-case-low current-limit threshold voltage
(from the Electrical Characteristics table) and the peak
inductor current:
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
systems can multiply the RESR value by a factor of 1.5
without hurting stability or transient response.
The output voltage ripple is usually dominated by the
filter capacitor’s ESR, and can be approximated as
IRIPPLE x RESR. There is also a capacitive term, so the
full equation for ripple in continuous-conduction mode
is V NOISE (p-p) = I RIPPLE x [R ESR + 1/(2 x π x f x
COUT)]. In Idle Mode, the inductor current becomes
discontinuous, with high peaks and widely spaced
pulses, so the noise can actually be higher at light load
(compared to full load). In Idle Mode, calculate the output ripple as follows:
VNOISE(p-p) =
0.02 x RESR
+
RSENSE
[
]
0.0003 x Lx 1 / VOUT + 1 / (VIN - VOUT )
2
(RSENSE ) x COUT
where: V SEC = the minimum required rectified secondary output voltage
VFWD = the forward drop across the secondary
rectifier
V OUT(MIN) = the minimum value of the main
output voltage (from the Electrical
Characteristics)
VRECT = the on-state voltage drop across the
synchronous rectifier MOSFET
VSENSE = the voltage drop across the sense
resistor
In positive-output applications, the transformer secondary return is often referred to the main output voltage, rather than to ground, to reduce the needed turns
ratio. In this case, the main output voltage must first be
subtracted from the secondary voltage to obtain VSEC.
Selecting Other Components
Transformer Design
(for Auxiliary Outputs Only)
Buck-plus-flyback applications, sometimes called “coupled-inductor” topologies, need a transformer to generate multiple output voltages. Performing the basic
electrical design is a simple task of calculating turns
ratios and adding the power delivered to the secondary
to calculate the current-sense resistor and primary
inductance. However, extremes of low input-output differentials, widely different output loading levels, and
high turns ratios can complicate the design due to parasitic transformer parameters such as interwinding
capacitance, secondary resistance, and leakage
inductance. For examples of what is possible with realworld transformers, see the Maximum Secondary
Current vs. Input Voltage graph in the Typical
Operating Characteristics section.
Power from the main and secondary outputs is combined to get an equivalent current referred to the main
output voltage (see the Inductor Value section for parameter definitions). Set the current-sense resistor resistor value at 80mV / ITOTAL.
PTOTAL = The sum of the output power from all outputs
ITOTAL = PTOTAL / VOUT = The equivalent output current referred to VOUT
L(primary) =
VOUT (VIN(MAX) - VOUT )
VIN(MAX) x f x ITOTAL x LIR
Turns Ratio N =
20
VSEC + VFWD
VOUT(MIN) + VRECT + VSENSE
MOSFET Switches
The high-current N-channel MOSFETs must be logic-level
types with guaranteed on-resistance specifications at
VGS = 4.5V. Lower gate threshold specifications are better (i.e., 2V max rather than 3V max). Drain-source breakdown voltage ratings must at least equal the maximum
input voltage, preferably with a 20% derating factor. The
best MOSFETs will have the lowest on-resistance per
nanocoulomb of gate charge. Multiplying RDS(ON) x QG
provides a good figure for comparing various MOSFETs.
Newer MOSFET process technologies with dense cell
structures generally perform best. The internal gate
drivers tolerate >100nC total gate charge, but 70nC is a
more practical upper limit to maintain best switching
times.
In high-current applications, MOSFET package power
dissipation often becomes a dominant design factor.
I2R power losses are the greatest heat contributor for
both high-side and low-side MOSFETs. I2R losses are
distributed between Q1 and Q2 according to duty factor (see the following equations). Generally, switching
losses affect only the upper MOSFET, since the
Schottky rectifier clamps the switching node in most
cases before the synchronous rectifier turns on. Gatecharge losses are dissipated by the driver and don’t
heat the MOSFET. Calculate the temperature rise
according to package thermal-resistance specifications
to ensure that both MOSFETs are within their maximum
junction temperature at high ambient temperature. The
worst-case dissipation for the high-side MOSFET
occurs at both extremes of input voltage, and the
worst-case dissipation for the low-side MOSFET occurs
at maximum input voltage.
______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
⎛ V x CRSS
⎞
+ VIN x ILOAD x f x ⎜ IN
+ 20ns⎟
⎝ IGATE
⎠
PD(lower FET) = (ILOAD )2 x RDS(ON) x (1 - DUTY)
DUTY = (VOUT + VQ2 ) / (VIN - VQ1)
where: on-state voltage drop VQ_ = ILOAD x RDS(ON)
CRSS = MOSFET reverse transfer capacitance
IGATE =DH driver peak output current capability (1A typical)
20ns = DH driver inherent rise/fall time
Under output short-circuit, the MAX1633/MAX1634/
MAX1635’s synchronous rectifier MOSFET suffers extra
stress because its duty factor can increase to greater
than 0.9. It may need to be oversized to tolerate a continuous DC short circuit. During short circuit, the
MAX1630/MAX1631/MAX1632’s output undervoltage
shutdown protects the synchronous rectifier under output short-circuit conditions.
To reduce EMI, add a 0.1µF ceramic capacitor from the
high-side switch drain to the low-side switch source.
Rectifier Clamp Diode
The rectifier is a clamp across the low-side MOSFET
that catches the negative inductor swing during the
60ns dead time between turning one MOSFET off and
each low-side MOSFET on. The latest generations of
MOSFETs incorporate a high-speed silicon body diode,
which serves as an adequate clamp diode if efficiency
is not of primary importance. A Schottky diode can be
placed in parallel with the body diode to reduce the forward voltage drop, typically improving efficiency 1% to
2%. Use a diode with a DC current rating equal to onethird of the load current; for example, use an MBR0530
(500mA-rated) type for loads up to 1.5A, a 1N5819 type
for loads up to 3A, or a 1N5822 type for loads up to
10A. The rectifier’s rated reverse breakdown voltage
must be at least equal to the maximum input voltage,
preferably with a 20% derating factor.
Boost-Supply Diode D2
A signal diode such as a 1N4148 works well in most
applications. If the input voltage can go below +6V, use
a small (20mA) Schottky diode for slightly improved
efficiency and dropout characteristics. Don’t use large
power diodes, such as 1N5817 or 1N4001, since high
junction capacitance can pump up VL to excessive
voltages.
Rectifier Diode D3
(Transformer Secondary Diode)
The secondary diode in coupled-inductor applications
must withstand flyback voltages greater than 60V,
which usually rules out most Schottky rectifiers.
Common silicon rectifiers, such as the 1N4001, are also
prohibited because they are too slow. This often makes
fast silicon rectifiers such as the MURS120 the only
choice. The flyback voltage across the rectifier is related to the VIN - VOUT difference, according to the transformer turns ratio:
VFLYBACK = VSEC + (VIN - VOUT ) x N
where: N = the transformer turns ratio SEC/PRI
V SEC = the maximum secondary DC output
voltage
VOUT = the primary (main) output voltage
Subtract the main output voltage (VOUT) from VFLYBACK
in this equation if the secondary winding is returned to
VOUT and not to ground. The diode reverse breakdown
rating must also accommodate any ringing due to leakage inductance. D3’s current rating should be at least
twice the DC load current on the secondary output.
Low-Voltage Operation
Low input voltages and low input-output differential
voltages each require extra care in their design. Low
absolute input voltages can cause the VL linear regulator to enter dropout and eventually shut itself off. Low
input voltages relative to the output (low VIN-VOUT differential) can cause bad load regulation in multi-output
flyback applications (see the design equations in the
Transformer Design section). Also, low VIN-VOUT differentials can also cause the output voltage to sag when
the load current changes abruptly. The amplitude of the
sag is a function of inductor value and maximum duty
factor (an Electrical Characteristics parameter, 98%
guaranteed over temperature at f = 200kHz), as follows:
VSAG =
(ISTEP )2 x L
2 x COUT x (VIN(MAX) x DMAX - VOUT )
The cure for low-voltage sag is to increase the output
capacitor’s value. For example, at VIN = +5.5V, VOUT =
+5V, L = 10µH, f = 200kHz, ISTEP = 3A, a total capacitance of 660µF keeps the sag less than 200mV. Note
that only the capacitance requirement increases, and
the ESR requirements don’t change. Therefore, the
added capacitance can be supplied by a low-cost bulk
capacitor in parallel with the normal low-ESR capacitor.
______________________________________________________________________________________
21
MAX1630–MAX1635
PD(upper FET) = (ILOAD )2 x RDS(ON) x DUTY
MAX1630–MAX1635
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Table 5. Low-Voltage Troubleshooting Chart
SYMPTOM
CONDITION
ROOT CAUSE
SOLUTION
Sag or droop in VOUT under
step-load change
Low VIN-VOUT
differential,
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