MAX1635EAI+ [ROCHESTER]
DUAL SWITCHING CONTROLLER, 300kHz SWITCHING FREQ-MAX, PDSO28, 5.30 MM, 0.65 MM PITCH, SSOP-28;型号: | MAX1635EAI+ |
厂家: | Rochester Electronics |
描述: | DUAL SWITCHING CONTROLLER, 300kHz SWITCHING FREQ-MAX, PDSO28, 5.30 MM, 0.65 MM PITCH, SSOP-28 信息通信管理 开关 光电二极管 |
文件: | 总30页 (文件大小:969K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
19-0480; Rev 4; 8/05
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
________________General Description
____________________________Features
♦ 96% Efficiency
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 on-
board power-up sequencing, power-good signaling with
delay, digital soft-start, secondary winding control, low-
dropout circuitry, internal frequency-compensation net-
works, and automatic bootstrapping.
♦ +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)
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 system-
suspend 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.
♦ 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)
These devices feature a logic-controlled and synchroniz-
able, fixed-frequency, pulse-width-modulation (PWM)
operating mode. This reduces noise and RF interference
in sensitive mobile communications and pen-entry appli-
cations. Asserting the SKIP pin enables fixed-frequency
mode, for lowest noise under all load conditions.
♦ 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
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 sig-
nal. SECFB provides a method for adjusting the sec-
ondary winding voltage regulation point with an external
resistor divider, and is intended to aid in creating auxiliary
voltages other than fixed 12V.
_______________Ordering Information
PART
TEMP RANGE
0°C to +70°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
MAX1630CAI
MAX1630CAI+
MAX1630EAI+
28 SSOP
28 SSOP
28 SSOP
Ordering Information continued at end of data sheet.
+ Denotes lead-free package.
________________Functional Diagram
The MAX1630/MAX1631/MAX1632 contain internal out-
put overvoltage and undervoltage protection features.
INPUT
________________________Applications
+12V
+5V (RTC)
+3.3V
5V
LINEAR
12V
LINEAR
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
Desktop CPU Local DC-DC Converters
+5V
3.3V
5V
SMPS
SMPS
Pin Configurations and Selector Guide appear at end of data
sheet.
POWER-UP
SEQUENCE
POWER-
GOOD
ON/OFF
RESET
Idle Mode and Dual Mode are trademarks of Maxim Integrated
Products.
________________________________________________________________ Maxim Integrated Products
1
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.
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,
VL, REF Short to GND ................................................Momentary
12OUT Short to GND..................................................Continuous
REF Current...........................................................+5mA to -1mA
VL Current.........................................................................+50mA
12OUT Current ...............................................................+200mA
V
Shunt Current............................................................+15mA
DD
Operating Temperature Ranges
SECFB, RESET to GND ............................................-0.3V to +6V
MAX163_CAI.......................................................0°C to +70°C
MAX163_EAI....................................................-40°C to +85°C
Storage Temperature Range.............................-65°C to +160°C
V
to GND............................................................-0.3V to +20V
RUN/ON3, SHDN to GND.............................-0.3V to (V+ + 0.3V)
12OUT to GND ...........................................-0.3V to (V + 0.3V)
DD
Continuous Power Dissipation (T = +70°C)
DD
A
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)
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, T = T
to T
, unless otherwise noted.
MAX
A
MIN
Typical values are at T = +25°C.)
A
PARAMETER
MAIN SMPS CONTROLLERS
Input Voltage Range
CONDITIONS
MIN
TYP
MAX
UNITS
4.2
30.0
2.58
V
V
3V Output Voltage in
Adjustable Mode
V+ = 4.2V to 30V, CSH3–CSL3 = 0V,
CSL3 tied to FB3
2.42
2.5
3.39
2.5
V+ = 4.2V to 30V, 0mV < CSH3–CSL3 < 80mV,
FB3 = 0V
3V Output Voltage in Fixed Mode
3.20
2.42
4.85
3.47
2.58
5.25
V
V
V
5V Output Voltage in
Adjustable Mode
V+ = 4.2V to 30V, CSH5–CSL5 = 0V,
CSL5 tied to FB5
V+ = 5.2V to 30V, 0mV < CSH–CSL5 < 80mV,
FB5 = 0V
5V Output Voltage in Fixed Mode
5.13
Output Voltage Adjust Range
Adjustable-Mode Threshold Voltage
Load Regulation
Either SMPS
REF
0.5
5.5
1.1
V
V
Dual Mode comparator
Either SMPS, 0V < CSH_–CSL_ < 80mV
Either SMPS, 5.2V < V+ < 30V
CSH3–CSL3 or CSH5–CSL5
-2
%
Line Regulation
0.03
100
-100
%/V
80
-50
10
120
-150
40
Current-Limit Threshold
Idle Mode Threshold
Soft-Start Ramp Time
mV
mV
Clk
SKIP = VL or V
< 13V or SECFB < 2.44V
DD
25
SKIP = 0V, not tested
From enable to 95% full current limit with respect to
512
f
(Note 1)
OSC
SYNC = VL
270
170
97
300
200
98
330
230
Oscillator Frequency
Maximum Duty Factor
kHz
%
SYNC = 0V
SYNC = VL
SYNC = 0V (Note 2)
98
99
2
_______________________________________________________________________________________
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, T = T
to T
, unless otherwise noted.
MAX
A
MIN
Typical values are at T = +25°C.)
A
PARAMETER
SYNC Input High Pulse Width
SYNC Input Low Pulse Width
SYNC Rise/Fall Time
CONDITIONS
MIN
200
TYP
MAX
UNITS
ns
Not tested
Not tested
Not tested
200
ns
200
350
ns
SYNC Input Frequency Range
240
kHz
V+ = VL = 0V,
CSL3 = CSH3 = CSL5 = CSH5 = 5.5V
Current-Sense Input Leakage Current
0.01
10
µA
FLYBACK CONTROLLER
V
Regulation Threshold
Falling edge (Note 3)
13
14
V
V
DD
SECFB Regulation Threshold
DL Pulse Width
Falling edge (MAX1631/MAX1634)
2.44
2.60
V
< 13V or SECFB < 2.44V
1
µs
V
DD
V
V
V
Shunt Threshold
Shunt Sink Current
Leakage Current
Rising edge, hysteresis = 1% (Note 3)
18
10
20
30
DD
DD
DD
V
V
= 20V (Note 3)
mA
µA
DD
DD
= 5V, off mode (Notes 3, 4)
12V LINEAR REGULATOR (Note 3)
12OUT Output Voltage
13V < V
< 18V, 0mA < I
< 120mA
11.65
12.1
150
50
12.50
100
V
DD
LOAD
12OUT Current Limit
12OUT forced to 11V, V
= 13V
mA
µA
DD
Quiescent V
Current
V
= 18V, run mode, no 12OUT load
DD
DD
INTERNAL REGULATOR AND REFERENCE
SHDN = V+, RUN/ON3 = TIME/ON5 = 0V,
5.3V < V+ < 30V, 0mA < I < 50mA
VL Output Voltage
4.7
3.5
5.1
3.7
V
V
LOAD
VL Undervoltage Lockout
Fault Threshold
Falling edge, hysteresis = 1%
3.6
VL Switchover Threshold
REF Output Voltage
Rising edge of CSL5, hysteresis = 1%
No external load (Note 5)
4.2
4.5
2.5
4.7
2.55
12.5
100.0
V
V
2.45
0µA < I
< 50µA
< 5mA
LOAD
REF Load Regulation
mV
0mA < I
LOAD
REF Sink Current
10
µA
V
REF Fault Lockout Voltage
V+ Operating Supply Current
Falling edge
1.8
2.4
50
VL switched over to CSL5, 5V SMPS on
5
µA
V+ = 5.5V to 30V, both SMPSs off,
includes current into SHDN
V+ Standby Supply Current
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
µA
V+ Shutdown Supply Current
4
10
4
V+ = 4V to 24V, SHDN = 0V
(Note 3)
2.5
Both SMPSs enabled, FB3 = FB5 = 0V,
CSL3 = CSH3 = 3.5V,
CSL5 = CSH5 = 5.3V
Quiescent Power Consumption
mW
MAX1631/
MAX1634
1.5
4
_______________________________________________________________________________________
3
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, T = T
to T
, unless otherwise noted.
MAX
A
MIN
Typical values are at T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
FAULT DETECTION (MAX1630/MAX1631/MAX1632)
Overvoltage Trip Threshold
Overvoltage-Fault Propagation Delay
Output Undervoltage Threshold
Output Undervoltage Lockout Time
Thermal Shutdown Threshold
RESET
With respect to unloaded output voltage
CSL_ driven 2% above overvoltage trip threshold
With respect to unloaded output voltage
4
7
10
%
µs
%
1.5
60
70
80
From each SMPS enabled, with respect to f
Typical hysteresis = +10°C
5000
6144
150
7000
Clk
°C
OSC
With respect to unloaded output voltage,
falling edge; typical hysteresis = 1%
-7
-5.5
1.5
-4
%
RESET Trip Threshold
Falling edge, CSL_ driven 2%
below RESET trip threshold
µs
RESET Propagation Delay
With respect to f
OSC
27,000 32,000 37,000
Clk
RESET Delay Time
INPUTS AND OUTPUTS
Feedback Input Leakage Current
FB3, FB5; SECFB = 2.6V
1
50
nA
V
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC
Logic Input Low Voltage
Logic Input High Voltage
0.6
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
SHDN, STEER, SYNC
2.4
V
RUN/ON3, SKIP, TIME/ON5 (SEQ = REF),
Input Leakage Current
1
µA
V
SHDN, STEER, SYNC, SEQ; V
= 0V or 3.3V
PIN
Logic Output Low Voltage
0.4
RESET, I
= 4mA
SINK
Logic Output High Current
TIME/ON5 Input Trip Level
TIME/ON5 Source Current
TIME/ON5 On-Resistance
Gate Driver Sink/Source Current
Gate Driver On-Resistance
1
mA
V
RESET = 3.5V
SEQ = 0V or VL
2.4
2.5
2.6
3.5
80
TIME/ON5 = 0V, SEQ = 0V or VL
3
15
1
µA
Ω
TIME/ON5; RUN/ON3 = 0V, SEQ = 0V or VL
DL3, DH3, DL5, DH5; forced to 2V
High or low
A
1.5
7
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 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 (V ) steered to it is disabled. In
DD
situations where the main outputs are being held up by external keep-alive supplies, turning off the 12OUT regulator pre-
vents a leakage path from the output-referred flyback winding, through the rectifier, and into V
.
DD
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
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, 3A Table 1 components, T = +25°C, unless otherwise noted.)
A
MAX1632/MAX1635
MAXIMUM 15V V OUTPUT
CURRENT vs. SUPPLY VOLTAGE
DD
EFFICIENCY vs. 3.3V OUTPUT CURRENT
EFFICIENCY vs. 5V OUTPUT CURRENT
800
100
100
V+ = 6V
V
> 13V
5V REGULATING
DD
V+ = 6V
90
80
70
60
90
80
70
60
600
400
200
0
5V LOAD = 0A
V+ = 15V
V+ = 15V
5V LOAD = 3A
ON5 = 5V
ON3 = 0V
f = 300kHz
MAX1631/MAX1634
ON3 = ON5 = 5V
f = 300kHz
MAX1631/MAX1634
50
50
0
5
10
15
20
0.001
0.01
0.1
1
10
0.001
0.01
0.1
1
10
SUPPLY VOLTAGE (V)
3.3V OUTPUT CURRENT (A)
5V OUTPUT CURRENT (A)
MAX1630/MAX1633
PWM MODE INPUT CURRENT
vs. INPUT VOLTAGE
IDLE MODE INPUT CURRENT
vs. INPUT VOLTAGE
MAXIMUM 15V V OUTPUT
DD
CURRENT vs. SUPPLY VOLTAGE
30
10
1
500
400
300
200
100
ON3 = ON5 = 5V
SKIP = 0V
NO LOAD
ON3 = ON5 = 5V
SKIP = VL
NO LOAD
V
> 13V
3.3V REGULATING
DD
25
20
15
10
3.3V LOAD = 0A
0.1
0.01
3.3V LOAD = 3A
5
0
0
0
5
10
15
20
25
30
0
5
10
15
20
25
30
0
5
10
SUPPLY VOLTAGE (V)
15
20
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
SHUTDOWN INPUT CURRENT
vs. INPUT VOLTAGE
STANDBY INPUT CURRENT
vs. INPUT VOLTAGE
MINIMUM V TO V
DIFFERENTIAL
IN
OUT
vs. 5V OUTPUT CURRENT
10
8
10,000
1000
100
10
1000
ON3 = ON5 = 0V
NO LOAD
SHDN = 0V
100
10
6
4
2
5V, 3A CIRCUIT
> 4.8V
V
OUT
f = 300kHz
0
1
1
0
5
10
15
20
25
30
0
5
10
15
20
25
30
0.001
0.01
0.1
1
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
5V OUTPUT CURRENT (A)
_______________________________________________________________________________________
5
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
____________________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, 3A Table 1 components, T = +25°C, unless otherwise noted.)
A
VL REGULATOR OUTPUT VOLTAGE
vs. OUTPUT CURRENT
SWITCHING FREQUENCY
vs. LOAD CURRENT
5.00
4.98
4.96
4.94
4.92
1000
100
+5V, V = 15V
IN
10
1
+3.3V, V = 15V
IN
+3.3V, V = 6V
IN
V
= 15V
IN
+5V, V = 6V
IN
ON3 = ON5 = 0V
4.90
0.1
0
10
20
30
40
50
60
0.1
1
10
100
1000
OUTPUT CURRENT (mA)
LOAD CURRENT (mA)
REF OUTPUT VOLTAGE
vs. OUTPUT CURRENT
START-UP WAVEFORMS
2.510
2.505
RUN
5V/div
2.500
2.495
2.490
3.3V OUTPUT
2V/div
TIME
5V/div
5V OUTPUT
5V/div
2.485
2.480
V
= 15V
IN
ON3 = ON5 = 0V
2ms/div
0
1
2
3
4
5
6
SEQ = VL, 0.015μF CAPACITOR ON-TIME
OUTPUT CURRENT (mA)
__________________________________________________________________________Pin Description
PIN
1
NAME
CSH3
CSL3
FUNCTION
Current-Sense Input for the 3.3V SMPS. Current-limit level is 100mV referred to CSL3.
2
Current-Sense Input. Also serves as the feedback input in fixed-output mode.
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.
3
4
FB3
12OUT
(MAX1630/
32/33/35)
12V/120mA Linear Regulator Output. Input supply comes from V . Bypass 12OUT to GND with
DD
1µF minimum.
Logic-Control Input for secondary feedback. Selects the PWM that uses a transformer and secondary
feedback signal (SECFB):
STEER
(MAX1631/
MAX1634)
STEER = GND: 3.3V SMPS uses transformer
STEER = VL: 5V SMPS uses transformer
6
_______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
_________________________________________________Pin Description (continued)
PIN
NAME
FUNCTION
V
DD
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.
(MAX1630/
32/33/35)
5
SECFB
Secondary Winding Feedback Input. Normally connected to a resistor divider from an auxiliary output.
(MAX1631/
MAX1634)
SECFB regulates at V
used.
= 2.5V (see Secondary Feedback Regulation Loop section). Tie to VL if not
SECFB
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.
6
7
SYNC
Dual-Purpose Timing Capacitor Pin and ON/OFF Control Input. See Power-Up Sequencing and
ON/OFF Controls section.
TIME/ON5
8
9
GND
REF
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.
10
SKIP
Active-Low Timed Reset Output. RESET swings GND to VL. Goes high after a fixed 32,000 clock-cycle
delay following power-up.
11
RESET
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.
12
FB5
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.
13
14
CSL5
CSH5
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
15
SEQ
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.
16
DH5
17
18
19
20
LX5
BST5
DL5
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
PGND
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 boot-
strapping. Bypass to GND with 4.7µF. VL supplies up to 25mA for external loads.
21
VL
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.
22
23
V+
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.
SHDN
24
25
26
DL3
BST3
LX3
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.
27
28
DH3
RUN/ON3
ON/OFF Control Input. See Power-Up Sequencing and ON/OFF Controls section.
_______________________________________________________________________________________
7
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
ON/OFF
INPUT
C3
+5V ALWAYS ON
4.7μF
10Ω
0.1μF
V+ SHDN SECFB VL
0.1μF
SYNC
BST3
4.7μF
0.1μF
BST5
DH5
Q3
Q4
Q1
Q2
DH3
LX3
DL3
0.1μF
L1
0.1μF
0.1μF
L2
R1
+5V OUTPUT
C1
R2
+3.3V OUTPUT
LX5
DL5
MAX1631
MAX1634
C2
*
*
PGND
CSH3
CSL3
FB3
CSH5
CSL5
FB5
RESET OUTPUT
RESET
TIME/ON5
RUN/ON3
5V ON/OFF
SKIP
3.3V ON/OFF
STEER
GND
REF
SEQ
+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)
of these circuits without first recalculating component
values (particularly inductance value at maximum bat-
tery voltage). Adding a Schottky rectifier across each
synchronous rectifier improves the efficiency of these
circuits by approximately 1%, but this rectifier is other-
wise 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.
_______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
_______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Table 1. Component Selection for Standard 3.3V/5V Application
LOAD CURRENT
COMPONENT
Input Range
2A
3A
4A
4.75V to 18V
PDA
4.75V to 28V
4.75V to 24V
Workstation
200kHz
Application
Frequency
Notebook
300kHz
300kHz
1/2 IR IRF7301;
IR IRF7403 or IRF7401 (18V
max); Siliconix Si4412DY; or
Motorola MMSF5N03HD or
MMSF5N02HD (18V max)
IR IRF7413 or
Siliconix Si4410DY
Q1, Q3 High-Side
MOSFETs
1/2 Siliconix Si9925DQ; or
1/2 Motorola MMDF3N03HD or
MMDF4N01HD (10V max)
1/2 IR IRF7301;
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 Siliconix Si9925DQ; or
1/2 Motorola MMDF3N03HD or
MMDF4N01HD (10V max)
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
C3 Input Capacitor
C1, C2 Output Capacitors
R1, R2 Resistors
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
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
10µH, 4A Ferrite
4.7µH, 5.5A Ferrite
Coilcraft DO3316P-153 or
Sumida CDRH125-150
Coilcraft DO3316P-103 or
Sumida CDRH125-100
Coilcraft DO3316-472 or
5.2µH, 6.5A Ferrite Sumida
CDRH127-5R2MC
L1, L2 Inductors
Table 2. Component Suppliers
FACTORY FAX
FACTORY FAX
(COUNTRY CODE)
COMPANY
USA PHONE
COMPANY
USA PHONE
(COUNTRY CODE)
AVX
(1) 803-626-3123
(803) 946-0690
(516) 435-1110
Motorola
Murata-Erie
NIEC
(1) 602-994-6430
(1) 814-238-0490
(81) 3-3494-7414
(81) 7-2070-1174
(1) 408-970-3950
(1) 603-224-1430
(81) 3-3607-5144
(1) 847-390-4428
(602) 303-5454
(814) 237-1431
(805) 867-2555*
(619) 661-6835
(408) 988-8000
(603) 224-1961
(847) 956-0666
(847) 390-4373
Central
Semiconductor
(1) 516-435-1824
Coilcraft
Coiltronics
Dale
(1) 847-639-1469
(1) 561-241-9339
(1) 605-665-1627
(847) 639-6400
(561) 241-7876
(605) 668-4131
Sanyo
Siliconix
Sprague
Sumida
TDK
International
Rectifier (IR)
(1) 310-322-3332
(310) 322-3331
IRC
(1) 512-992-3377
(1) 714-960-6492
(512) 992-7900
(714) 969-2491
Transpower
Technologies
(1) 702-831-3521
(702) 831-0140
Matsuo
*Distributor
_______________________________________________________________________________________
9
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
INPUT
SHDN
V+
SYNC
CSL5
-
MAX1632
+
4.5V
ON/OFF
5V
LINEAR
REG
12OUT
+12V
12V
LINEAR
REG
+5V ALWAYS ON
VL
IN
V
DD
REF
SECFB
+
-
2.5V
REF
13V
RAW +15V
BST3
BST5
DH3
LX3
DH5
LX5
3.3V
PWM
LOGIC
5V
PWM
LOGIC
200kHz
TO
300kHz
OSC
+5V
+3.3V
VL
VL
DL3
DL5
PGND
OV/UV
FAULT
CSH3
CSL3
+
-
CSH5
CSL5
REF
REF
-
+
LPF
60kHz
LPF
60kHz
1.75V
2.68V
2.388V
-
R1
R2
-
R3
FB3
FB5
OUTPUTS
UP
-
-
R4
+
+
0.6V
0.6V
RESET
SEQ
VL
TIMER
2.6V
-
TIME/ON5
+
+
POWER-ON
SEQUENCE
LOGIC
REF
-
+
1V
-
RUN/ON3
GND
Figure 2. MAX1632 Block Diagram
10 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
PWM Controller Block
_______________Detailed Description
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 con-
troller 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 sig-
nal, and the slope compensation ramp (Figure 3). The
PWM controller is a direct-summing type, lacking a tra-
ditional error amplifier and the phase shift associated
with it. This direct-summing configuration approaches
ideal cycle-by-cycle control over the output voltage.
The MAX1630 is a dual, BiCMOS, switch-mode power-
supply controller designed primarily for buck-topology
regulators in battery-powered applications where high effi-
ciency and low quiescent supply current are critical. Light-
load efficiency is enhanced by automatic Idle Mode™
operation, a variable-frequency pulse-skipping mode that
reduces transition and gate-charge losses. Each step-
down, 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_.
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 opera-
tion as load current increases.
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 multi-
plexer, 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 overvolt-
age. A power-on sequence block controls the power-
up timing of the main PWMs and determines whether
one or both of the outputs are monitored for undervolt-
age 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, adjustable-
output, coupled-inductor flyback winding to be attached
to either the 3.3V or the 5V main inductor. Bias genera-
tor blocks include the 5V IC internal rail (VL) linear regu-
lator, 2.5V precision reference, and automatic bootstrap
switchover circuit. The PWMs share a common
200kHz/300kHz synchronizable oscillator.
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
/V ). As the
OUT IN
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
LOAD
SKIP
MODE
DESCRIPTION
CURRENT
Pulse-skipping, supply cur-
rent = 250µA at V = 12V,
IN
Low
Light
Idle
discontinuous inductor
current
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.
Constant-frequency PWM,
continuous inductor current
Low
High
High
Heavy
Light
PWM
PWM
PWM
Constant-frequency PWM,
continuous inductor current
Constant-frequency PWM,
continuous inductor current
Heavy
______________________________________________________________________________________ 11
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
CSH_
CSL_
1X
REF
FROM
FEEDBACK
DIVIDER
MAIN PWM
COMPARATOR
BST_
DH_
LX_
R
Q
LEVEL
SHIFT
S
SLOPE COMP
OSC
30mV
SKIP
CURRENT
LIMIT
DAC
SHOOT-
THROUGH
CONTROL
CK
COUNTER
SHDN
SOFT-START
SYNCHRONOUS
RECTIFIER CONTROL
VL
R
S
Q
LEVEL
SHIFT
DL_
-100mV
PGND
REF
1μs
SINGLE-SHOT
SECFB
Figure 3. PWM Controller Detailed Block Diagram
12 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
In PWM mode, the controller operates as a fixed-
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 intro-
duced by the output capacitor’s parasitic resistance
(ESR) (see Design Procedure section). A 60kHz pole-
zero cancellation filter provides additional rolloff above
the unity-gain crossover. This internal 60kHz lowpass
compensation filter cancels the zero due to filter capaci-
tor ESR. The 60kHz filter is included in the loop in both
fixed-output and adjustable-output modes.
frequency current-mode controller where the duty ratio
is set by the input/output voltage ratio. The current-
mode 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 (voltage-
mode) PWM, to a higher frequency. To preserve inner-
loop 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%.
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 synchro-
nous rectifier ensures proper start-up of the boost gate-
driver circuit. If the synchronous power MOSFETs are
omitted for cost or other reasons, replace them with a
small-signal MOSFET, such as a 2N7002.
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.
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 “shoot-
through”). In discontinuous (light-load) mode, the syn-
chronous switch is turned off as the inductor current
falls through zero. The synchronous rectifier works
VL
R1
R2
TO PWM
LOGIC
UNCOMPENSATED
HIGH-SPEED
FB_
LEVEL TRANSLATOR
AND BUFFER
OUTPUT DRIVER
I1
I2
I3
V
BIAS
REF
CSH_
CSL_
SLOPE COMPENSATION
Figure 4. Main PWM Comparator Block Diagram
______________________________________________________________________________________ 13
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 cross-
regulation (see Secondary Feedback Regulation Loop
section).
turns on the high-side MOSFET by closing an internal
switch between BST_ and DH_. This provides the nec-
essary 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 nat-
ural operating condition. It is caused by residual ener-
gy 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.
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 regula-
tor 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 cir-
cuit (10mA to 100mA Schottky or 1N4148 are pre-
ferred), and bypass V+ to PGND with 4.7µF directly at
the package pins.
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
The 2.5V reference (REF) is accurate to 2% over tem-
perature, making REF useful as a precision system ref-
erence. 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 refer-
ence load-regulation error.
80mV/I
, where I
is the required peak inductor
PEAK
PEAK
current to support the full load current, while compo-
nents must be designed to withstand continuous cur-
rent 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.
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.
The CSL5 input also serves as the IC’s bootstrap sup-
ply input. Whenever V
connects CSL5 to VL.
> 4.5V, an internal switch
CSL5
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.
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 par-
allel to the high-side MOSFET’s gate-source terminals.
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 dif-
ferences (see Low-Voltage Operation section).
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 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Shutdown Mode
Holding SHDN low puts the IC into its 4µA shutdown
mode. SHDN is logic input with a threshold of about 1V
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 under-
voltage 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.
(the V
of an internal N-channel MOSFET). For auto-
TH
matic start-up, bypass SHDN to GND with a 0.01µF
capacitor and connect it to V+ through a 220kΩ resistor.
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 driv-
ing 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 inter-
nal discharge pull-down transistor, which turns on in
standby mode and momentarily at the first power-up or
in shutdown mode.
Output Overvoltage Protection
(MAX1630/MAX1631/MAX1632)
Both SMPS outputs are monitored for overvoltage. If
either output is more than 7% above the nominal regu-
lation 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.
RESET Power-Good Voltage Monitor
The power-good monitor generates a system RESET sig-
nal. 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.
Table 4. Operating Modes
SEQ
RUN/ON3
TIME/ON5
X
MODE
DESCRIPTION
SHDN
Low
X
X
Shutdown
Standby
Run
All circuit blocks turned off. Supply current = 4µA.
Both SMPSs off. Supply current = 30µA.
3.3V SMPS enabled/5V off
High
High
High
High
High
High
High
High
Ref
Ref
Ref
Ref
GND
GND
VL
Low
Low
High
Low
Low
High
Run
5V SMPS enabled/3.3V off
High
Low
High
Run
Both SMPSs enabled
Timing capacitor
Timing capacitor
Timing capacitor
Timing capacitor
Standby
Run
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.
High
Low
Standby
Run
VL
High
X = Don’t Care
______________________________________________________________________________________ 15
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).
Internal Digital Soft-Start Circuit
Soft-start allows a gradual increase of the internal cur-
rent-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 con-
verter (DAC), and a current-limit comparator. In shut-
down 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 incre-
menting the comparison voltage applied to the current-
limit 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.
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 overvolt-
age 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 hot-
swap power supplies); in such cases, the MAX1633,
MAX1634, or MAX1635 should be used.
Dropout Operation
Dropout (low input-output differential operation) is
enhanced by stretching the clock pulse width to
increase the maximum duty factor. The algorithm fol-
Low-Noise Operation (PWM Mode)
PWM mode (SKIP = high) minimizes RF and audio
interference in noise-sensitive applications (such as hi-
fi multimedia-equipped systems), cellular phones, RF
communicating computers, and electromagnetic pen-
entry systems. See the summary of operating modes in
Table 2. SKIP can be driven from an external logic
signal.
lows: If the output voltage (V
) drops out of regula-
OUT
tion 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 regula-
tion, 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.
Interference due to switching noise is reduced in PWM
mode by ensuring a constant switching frequency, thus
concentrating the emissions at a known frequency out-
side 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-regula-
tion range, constant operating frequency is not main-
tained under overload or dropout conditions (see
Overload and Dropout Operation section.)
The typical PWM minimum off-time is 300ns, regardless
of the operating frequency. Lowering the operating fre-
quency 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 volt-
age with external resistors is simple for any of the
MAX1630 family ICs, through resistor dividers connect-
ed to FB3 and FB5 (Figure 2). Calculate the output volt-
age with the following formula:
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 reverse-
current limit from 0mV to -100mV, allowing the inductor
current to reverse at light loads. This results in fixed-
frequency operation and continuous inductor-current
flow. This eliminates discontinuous-mode inductor ring-
ing and improves cross regulation of transformer-
coupled multiple-output supplies, particularly in circuits
that don’t use additional secondary regulation via
V
OUT
= V
(1 + R1 / R2)
REF
where V
= 2.5V nominal.
REF
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_.
SECFB or V
.
DD
In most applications, tie SKIP to GND to minimize qui-
escent supply current. VL supply current with SKIP high
is typically 20mA, depending on external MOSFET gate
capacitance and switching losses.
16 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
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.
R2
SECFB
1-SHOT
TRIG
R1
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 lin-
early regulating, and as low as 4.2V when automatically
bootstrapped to CSH5.
POSITIVE
SECONDARY
OUTPUT
V+
2.5V REF
DH_
MAIN
OUTPUT
MAX1631
MAX1634
Secondary Feedback Regulation Loop
DL_
(SECFB or V
)
DD
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
R1
+V = V (1 + –––)
WHERE V (NOMINAL) = 2.5V
REF
TRIP
REF
R2
input-output differential voltage. If V
or SECFB falls
DD
Figure 5. Adjusting the Secondary Output Voltage with SECFB
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 oper-
ate in forward mode. The low impedance presented by
the transformer secondary in forward mode dumps cur-
rent into the secondary output, charging up the sec-
+12V OUTPUT
200mA
12OUT
0.1μF
10μF
V
DD
2N3906
ondary capacitor and bringing V
or SECFB back into
DD
0.1μF
10Ω
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.
0.1μF
MAX1630
MAX1632
MAX1633
MAX1635
V+
V
DD
OUTPUT
2.2μF
DH_
DL_
Devices with a 12OUT linear regulator have a V
pin
DD
MAIN
OUTPUT
that regulates at a fixed 13.5V, set by an internal resis-
tor 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 nor-
mally 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.
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
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
for high-efficiency, battery-powered applications. See
Appendix A in Maxim’s Battery Management and DC-
DC Converter Circuit Collection for crossover-point and
discontinuous-mode equations. Discontinuous conduc-
tion doesn’t affect normal Idle Mode operation.
Maximum 15V V
Output Current vs. Supply Voltage
DD
graphs in the Typical Operating Characteristics).
Three key inductor parameters must be specified:
__________________Design Procedure
inductance value (L), peak current (I
), and DC
PEAK
The three predesigned 3V/5V standard application cir-
cuits (Figure 1 and Table 1) contain ready-to-use solu-
tions 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 require-
ments. But before beginning a design, firmly establish
the following:
resistance (R ). The following equation includes a
DC
constant, LIR, which is the ratio of inductor peak-to-
peak 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 load-
current ratio (LIR = 0.3), which corresponds to a peak
inductor current 1.15 times higher than the DC load
current.
Maximum input (battery) voltage, V
. This
IN(MAX)
V
(V
- V
)
OUT IN(MAX)
x f x I
OUT
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.
L =
V
x LIR
OUT
IN(MAX)
where: f = switching frequency, normally 200kHz or
300kHz
V
must not exceed 30V.
IN(MAX)
Minimum input (battery) voltage, V
. This
IN(MIN)
I
= maximum DC load current
OUT
should be taken at full load under the lowest battery
conditions. If V is less than 4.2V, use an external
IN(MIN)
LIR = ratio of AC to DC inductor current, typi-
cally 0.3; should be selected for >0.15
circuit to externally hold VL above the VL undervoltage
lockout threshold. If the minimum input-output differ-
ence is less than 1.5V, the filter capacitance required to
maintain good AC load regulation increases (see Low-
Voltage Operation section).
The nominal peak inductor current at full load is 1.15 x
I
if the above equation is used; otherwise, the peak
OUT
current can be calculated by:
V
(V
- V
)
OUT IN(MAX)
OUT
I
= I
+
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 I2R
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
PEAK
LOAD
2 x f x L x V
IN(MAX)
The inductor’s DC resistance should be low enough that
R
x I < 100mV, as it is a key parameter for effi-
DC
PEAK
ciency performance. If a standard off-the-shelf inductor
is not available, choose a core with an LI2 rating greater
than L x I
2 and wind it with the largest-diameter
PEAK
wire that fits the winding area. For 300kHz applications,
ferrite core material is strongly preferred; for 200kHz
®
applications, Kool-Mu (aluminum alloy) or even pow-
dered iron is acceptable. If light-load efficiency is unim-
portant (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.
can affect load-transient response (see the V
equa-
SAG
tion in the Low-Voltage Operation section). The equa-
tions that follow are for continuous-conduction
operation, since the MAX1630 family is intended mainly
Kool-Mu is a registered trademark of Magnetics Div., Spang & Co.
18 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
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:
Bypassing VL
Bypass the VL output with a 4.7µF tantalum capacitor
paralleled with a 0.1µF ceramic capacitor, close to the
device.
Output Filter Capacitor Value
The output filter capacitor values are generally deter-
mined 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 capaci-
tance than is required for AC stability. Use only special-
ized 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:
80mV
R
=
SENSE
I
PEAK
Use I
from the second equation in the Inductor
PEAK
Value section
Use the calculated value of R
to size the MOSFET
SENSE
switches and specify inductor saturation-current ratings
according to the worst-case high-current-limit threshold
voltage:
120mV
I
=
PEAK(MAX)
R
V
(1 + V
/ V
)
SENSE
REF
OUT
IN(MIN)
C
R
>
OUT
V
x R
x f
SENSE
Low-inductance resistors, such as surface-mount
metal-film, are recommended.
OUT
R
x V
OUT
SENSE
V
<
ESR
Input Capacitor Value
Connect low-ESR bulk capacitors and small ceramic
capacitors (0.1µF) directly to the drains on the high-
side 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
REF
(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 cost-
conscious 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-tran-
sient waveform has enough ringing on it that the peak
noise levels exceed the allowable output voltage toler-
ance. Note that even with zero phase margin and gross
instability present, the output voltage noise never gets
current (I
) is determined by the input voltage and
RMS
load current, with the worst case occurring at V = 2 x
IN
V
:
OUT
V
(V - V
)
OUT IN OUT
I
= I
x
RMS
LOAD
V
IN
Therefore, when V is 2 x V
:
IN
OUT
I
LOAD
2
I
=
RMS
Bypassing V+
Bypass the V+ input with a 4.7µF tantalum capacitor
paralleled with a 0.1µF ceramic capacitor, close to the
much worse than I
x R
(under constant loads).
PEAK
ESR
Designers of RF communicators or other noise-sensi-
tive analog equipment should be conservative and stay
within the guidelines. Designers of notebook computers
and similar commercial-temperature-range digital
IC. A 10Ω series resistor to V is also recommended.
IN
______________________________________________________________________________________ 19
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
systems can multiply the R
value by a factor of 1.5
where: V
= the minimum required rectified sec-
ondary output voltage
ESR
SEC
without hurting stability or transient response.
The output voltage ripple is usually dominated by the
filter capacitor’s ESR, and can be approximated as
RIPPLE
V
V
= the forward drop across the secondary
rectifier
FWD
I
x R
. There is also a capacitive term, so the
ESR
= the minimum value of the main
output voltage (from the Electrical
Characteristics)
OUT(MIN)
full equation for ripple in continuous-conduction mode
is V = I x [R + 1/(2 x π x f x
NOISE (p-p)
RIPPLE
ESR
C
)]. In Idle Mode, the inductor current becomes
OUT
V
V
= the on-state voltage drop across the
synchronous rectifier MOSFET
RECT
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 out-
put ripple as follows:
= the voltage drop across the sense
resistor
SENSE
In positive-output applications, the transformer sec-
ondary return is often referred to the main output volt-
age, rather than to ground, to reduce the needed turns
ratio. In this case, the main output voltage must first be
0.02 x R
ESR
V
=
+
NOISE(p-p)
R
SENSE
0.0003 x Lx 1 / V
+1 / (V - V
)
]
[
OUT
2
IN OUT
) x C
OUT
subtracted from the secondary voltage to obtain V
.
SEC
(R
SENSE
Selecting Other Components
MOSFET Switches
The high-current N-channel MOSFETs must be logic-level
types with guaranteed on-resistance specifications at
Transformer Design
(for Auxiliary Outputs Only)
Buck-plus-flyback applications, sometimes called “cou-
pled-inductor” topologies, need a transformer to gener-
ate 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 dif-
ferentials, widely different output loading levels, and
high turns ratios can complicate the design due to par-
asitic transformer parameters such as interwinding
capacitance, secondary resistance, and leakage
inductance. For examples of what is possible with real-
world transformers, see the Maximum Secondary
Current vs. Input Voltage graph in the Typical
Operating Characteristics section.
V
= 4.5V. Lower gate threshold specifications are bet-
GS
ter (i.e., 2V max rather than 3V max). Drain-source break-
down 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 R
x Q
G
DS(ON)
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 fac-
tor (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. Gate-
charge 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.
Power from the main and secondary outputs is com-
bined to get an equivalent current referred to the main
output voltage (see the Inductor Value section for para-
meter definitions). Set the current-sense resistor resis-
tor value at 80mV / I
.
TOTAL
P
= The sum of the output power from all outputs
TOTAL
TOTAL
I
= P
/ V
= The equivalent output cur-
OUT
TOTAL
rent referred to V
OUT
V
(V
- V
)
OUT IN(MAX)
OUT
L(primary) =
V
x f x I
x LIR
TOTAL
IN(MAX)
V
+ V
FWD
SEC
Turns Ratio N =
V
+V
+V
OUT(MIN)
RECT SENSE
20 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Rectifier Diode D3
2
PD(upper FET)= (I
) x R
x DUTY
DS(ON)
LOAD
(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 relat-
⎛
⎞
V
x C
RSS
IN
I
+V x I
x f x
+ 20ns
⎟
IN
LOAD
⎜
⎝
⎠
GATE
2
PD(lower FET) = (I
) x R
x (1 - DUTY)
LOAD
DS(ON)
+V ) / (V - V )
Q2 IN Q1
DUTY = (V
OUT
where: on-state voltage drop V = I
x R
DS(ON)
ed to the V - V
difference, according to the trans-
OUT
Q_
LOAD
IN
former turns ratio:
C
I
= MOSFET reverse transfer capacitance
RSS
=DH driver peak output current capabil-
ity (1A typical)
V
= V
+ (V - V
) x N
GATE
FLYBACK
SEC
IN OUT
20ns = DH driver inherent rise/fall time
where: N = the transformer turns ratio SEC/PRI
V
= the maximum secondary DC output
voltage
= the primary (main) output voltage
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 con-
tinuous DC short circuit. During short circuit, the
MAX1630/MAX1631/MAX1632’s output undervoltage
shutdown protects the synchronous rectifier under out-
put short-circuit conditions.
SEC
V
OUT
Subtract the main output voltage (V
in this equation if the secondary winding is returned to
and not to ground. The diode reverse breakdown
rating must also accommodate any ringing due to leak-
age inductance. D3’s current rating should be at least
twice the DC load current on the secondary output.
) from V
OUT FLYBACK
V
OUT
To reduce EMI, add a 0.1µF ceramic capacitor from the
high-side switch drain to the low-side switch source.
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 regula-
tor to enter dropout and eventually shut itself off. Low
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 for-
ward voltage drop, typically improving efficiency 1% to
2%. Use a diode with a DC current rating equal to one-
third 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.
input voltages relative to the output (low V -V
dif-
IN OUT
ferential) can cause bad load regulation in multi-output
flyback applications (see the design equations in the
Transformer Design section). Also, low V -V
differ-
IN OUT
entials 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:
2
(I
) x L
STEP
V
=
SAG
2 x C
x (V
x D
- V
)
OUT
IN(MAX)
MAX
OUT
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.
The cure for low-voltage sag is to increase the output
capacitor’s value. For example, at V = +5.5V, V
=
OUT
IN
+5V, L = 10µH, f = 200kHz, I
= 3A, a total capaci-
STEP
tance 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
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Table 5. Low-Voltage Troubleshooting Chart
SYMPTOM
CONDITION
ROOT CAUSE
SOLUTION
Increase bulk output capacitance
per formula (see Low-Voltage
Operation section). Reduce inductor
value.
Sag or droop in V
step-load change
under
Low V -V
differential, <1.5V
Limited inductor-current
slew rate per cycle.
OUT
IN OUT
Dropout voltage is too high
(V follows V as V
decreases)
Reduce operation to 200kHz.
Reduce MOSFET on-resistance and
coil DCR.
Low V -V
differential, <1V
Maximum duty-cycle limits
exceeded.
IN OUT
OUT
IN
IN
Unstable—jitters between
different duty factors and
frequencies
Low V -V
differential, <0.5V
Normal function of internal
low-dropout circuitry.
Increase the minimum input voltage
or ignore.
IN OUT
Not enough duty cycle left
to initiate forward-mode
operation. Small AC current
in primary can’t store ener-
gy for flyback operation.
Reduce operation to 200kHz.
Reduce secondary impedances;
use a Schottky diode, if possible.
Stack secondary winding on the
main output.
Low V -V
IN OUT
Secondary output won’t
support a load
differential,
< 1.3 x V
V
IN
(main)
OUT
VL linear regulator is going
into dropout and isn’t provid-
ing good gate-drive levels.
Use a small 20mA Schottky diode
for boost diode D2. Supply VL from
an external source.
Poor efficiency
Low input voltage, <5V
Low input voltage, <4.5V
Won’t start under load or
quits before battery is
completely dead
Supply VL from an external source
VL output is so low that it
hits the VL UVLO threshold.
other than V , such as the system
IN
+5V supply.
where R
is the DC resistance of the coil, R
is
DC
DS(ON)
is the current-
________________Applications Information
Heavy-Load Efficiency Considerations
The major efficiency-loss mechanisms under loads are,
in the usual order of importance:
the MOSFET on-resistance, and R
SENSE
sense resistor value. The R
term assumes identi-
DS(ON)
cal MOSFETs for the high-side and low-side switches,
because they time-share the inductor current. If the
MOSFETs aren’t identical, their losses can be estimat-
ed by averaging the losses according to duty factor.
• P(I2R) = I2R losses
• P(tran) = transition losses
• P(gate) = gate-charge losses
• P(diode) = diode-conduction losses
• P(cap) = capacitor ESR losses
3
2
PD(tran)= transition loss = V x I
x f x
x
IN LOAD
(V x C
/ I
) + 20ns
IN
RSS GATE
where C
is the reverse transfer capacitance of the
RSS
• P(IC) = losses due to the IC’s operating supply
supply current
high-side MOSFET (a data-sheet parameter), I
is the
GATE
DH gate-driver peak output current (1.5A typical), and
20ns is the rise/fall time of the DH driver (20ns typical).
Inductor core losses are fairly low at heavy loads
because the inductor’s AC current component is small.
Therefore, they aren’t accounted for in this analysis.
Ferrite cores are preferred, especially at 300kHz, but
powdered cores, such as Kool-Mu, can work well.
P(gate) = qG x f x VL
where VL is the internal-logic-supply voltage (+5V), and qG
is the sum of the gate-charge values for low-side and high-
side switches. For matched MOSFETs, qG is twice the
data-sheet value of an individual MOSFET. If V
less than 4.5V, replace VL in this equation with V
this case, efficiency can be improved by connecting VL to
an efficient 5V source, such as the system +5V supply.
Efficiency = P
/ P x 100%
IN
is set to
OUT
OUT
. In
BATT
= P
/ (P
+ P
) x 100%
OUT
OUT
TOTAL
2
P
= P(I R) + P(tran) + P(gate) +
TOTAL
P(diode) + P(cap) + P(IC)
P(diode)= diode- conduction losses
2
2
P = (I R)= (I
) x (R
+ R
+ R
)
= I
x V
x t x f
LOAD
DC
DS(ON)
SENSE
LOAD
FWD D
22 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
where t is the diode-conduction time (120ns typical)
Rectifier diode cathode to low-side
MOSFET: 5mm max length
D
and V
is the forward voltage of the diode.
FWD
LX node (MOSFETs, rectifier cathode,
inductor): 15mm max length
This power is dissipated in the MOSFET body diode if
no external Schottky diode is used.
Ideally, surface-mount power components are butted
up to one another with their ground terminals almost
touching. These high-current grounds are then con-
nected to each other with a wide filled zone of top-layer
copper so they don’t go through vias. The resulting top-
layer “sub-ground-plane” is connected to the normal
inner-layer ground plane at the output ground termi-
nals, which ensures that the IC’s analog ground is
sensing at the supply’s output terminals without interfer-
ence from IR drops and ground noise. Other high-
current paths should also be minimized, but focusing
primarily on short ground and current-sense con-
nections eliminates about 90% of all PC board lay-
out problems (see the PC board layouts in the
MAX1630 Evaluation Kit manual for examples).
2
P(cap) = input capacitor ESR loss = (I
)
x R
ESR
RMS
where I
is the input ripple current as calculated in the
Design Procedure and Input Capacitor Value sections.
RMS
Light-Load Efficiency Considerations
Under light loads, the PWM operates in discontinuous
mode, where the inductor current discharges to zero at
some point during the switching cycle. This makes the
inductor current’s AC component high compared to the
load current, which increases core losses and I2R loss-
es in the output filter capacitors. For best light-load effi-
ciency, use MOSFETs with moderate gate-charge
levels, and use ferrite, MPP, or other low-loss core
material. Avoid powdered-iron cores; even Kool-Mu
(aluminum alloy) is not as good as ferrite.
2) Place the IC and signal components. Keep the main
switching nodes (LX nodes) away from sensitive
analog components (current-sense traces and REF
capacitor). Place the IC and analog components on
the opposite side of the board from the power-
switching node. Important: the IC must be no far-
ther than 10mm from the current-sense resistors.
Keep the gate-drive traces (DH_, DL_, and BST_)
shorter than 20mm and route them away from CSH_,
CSL_, and REF.
PC Board Layout Considerations
Good PC board layout is required in order to achieve
specified noise, efficiency, and stability performance.
The PC board layout artist must be given explicit
instructions, preferably a pencil sketch showing the
placement of power-switching components and high-
current routing. See the PC board layout in the
MAX1630 Evaluation Kit manual for examples. A
ground plane is essential for optimum performance. In
most applications, the circuit will be located on a multi-
layer board, and full use of the four or more copper lay-
ers is recommended. Use the top layer for high-current
connections, the bottom layer for quiet connections
(REF, SS, GND), and the inner layers for an uninterrupt-
ed ground plane. Use the following step-by-step guide:
3) Use a single-point star ground where the input
ground trace, power ground (sub-ground-plane),
and normal ground plane meet at the supply’s out-
put ground terminal. Connect both IC ground pins
and all IC bypass capacitors to the normal ground
plane.
1) Place the high-power components (Figure1, C1, C3,
Q1, Q2, D1, L1, and R1) first, with any grounded
connections adjacent.
HIGH CURRENT PATH
Priority 1: Minimize current-sense resistor trace
lengths and ensure accurate current
sensing with Kelvin connections (Figure 7).
SENSE RESISTOR
Priority 2: Minimize ground trace lengths in the
high-current paths (discussed below).
Priority 3: Minimize other trace lengths in the high-
current paths.
Use >5mm-wide traces
C
to high-side MOSFET drain: 10mm
MAX1630
IN
max length
Figure 7. Kelvin Connections for the Current-Sense Resistors
______________________________________________________________________________________ 23
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
_______________________________________________________________________________Application Circuits
*
*
TO +3.3V OUTPUT
TO +5V OUTPUT
C4
INPUT
+5.2V TO +24V
C3
10Ω
0.1μF
4.7μF
+5V
ALWAYS ON
ON/OFF
4.7μF
0.1μF
23 22
6
21
VL
V+
SHDN
SYNC
5
4
+12V
AT 120mA
12OUT
V
DD
2.2μF
25
27
18
16
2.7μF
BST3
DH3
BST5
DH5
Q3
Q1
0.1μF
L2
C1
R2
+5V OUTPUT (3A)
C2
+3.3V
OUTPUT
(3A)
0.1μF
0.1μF
Q4
26
24
17
19
T1
1:4
LX5
DL5
R1
LX3
DL3
MAX1630
MAX1633
0.1μF
*
*
Q2
20
14
PGND
1N5819
1N5819
1
CSH3
CSL3
FB3
CSH5
CSL5
FB5
13
12
2
3
15
9
28
7
3V ON/OFF
5V ON/OFF
SEQ
REF
RUN/ON3
TIME/ON5
+2.5V REF
1μF
11
RESET
POWER-GOOD
SKIP
10
GND
8
R1 = R2 = 20mΩ
L2 = 10μH SUMIDA CDRH125-100
T1 = 10μH 1:4 TRANSFORMER
TRANSPOWER TECHNOLOGIES TTI-5902
Q1–Q4 = Si4410DY or IRF7413
C1 = 3 x 220μF 10V SPRAGUE 594D227X0010D2T
C2 = 2 x 220μF 10V SPRAGUE 594D227X0010D2T
C3 = C4 = 2 x 10μF 30V SANYO OS-CON 30SC10M
*VL DIODES AND OUTPUT SCHOTTKY DIODES REQUIRED
FOR THE MAX1630 ONLY (SEE OUTPUT OVERVOLTAGE PROTECTION
AND OUTPUT UNDERVOLTAGE SHUTDOWN PROTECTION SECTIONS).
Figure 8. Triple-Output Application for Low-Voltage Batteries (MAX1630/MAX1633)
24 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
_____________________________________________________________Application Circuits (continued)
*
*
TO +3.3V OUTPUT
TO +5V OUTPUT
C4
INPUT
+6.5V TO +28V
C3
10Ω
0.1μF
4.7μF
+5V ALWAYS ON
ON/OFF
0.1μF
4.7μF
23
22
V+
6
21
VL
SHDN
SYNC
+12V AT 120mA
4
5
12OUT
2.2μF
V
DD
D2
D1
2.2μF
D5
25
18
16
BST3
DH3
BST5
DH5
Q1
Q3
27
L1
0.1μF
+3.3V OUTPUT (3A)
C1
R2
+5V OUTPUT (3A)
C2
*
0.1μF
0.1μF
26
24
17
19
20
T2
1:2.2
LX5
R1
LX3
DL3
MAX1632
MAX1635
0.1μF
*
DL5
Q2
Q4
PGND
1N5819
1N5819
1
14
13
12
CSH3
CSL3
FB3
CSH5
CSL5
FB5
2
3
15
9
28
7
3V ON/OFF
5V ON/OFF
SEQ
REF
RUN/ON3
TIME/ON5
+2.5V REF
1μF
11
RESET
POWER-GOOD
SKIP
10
GND
8
R1 = R2 = 20mΩ
L1 = 10μH SUMIDA CDRH125-100
T2 = 10μH 1:2.2 TRANSFORMER
TRANSPOWER TECHNOLOGIES TTI-5870
Q1–Q4 = Si4410DY or IRF7413
C1 = 3 x 220μF 10V SPRAGUE 594D227X0010D2T
C2 = 2 x 220μF 10V SPRAGUE 594D227X0010D2T
C3 = C4 = 2 x 10μF 30V SANYO OS-CON 30SC10M
*VL DIODES AND OUTPUT SCHOTTKY DIODES REQUIRED
FOR THE MAX1632 ONLY (SEE OUTPUT OVERVOLTAGE PROTECTION
AND OUTPUT UNDERVOLTAGE SHUTDOWN PROTECTION SECTIONS).
Figure 9. Triple-Output Application for High-Voltage Batteries (MAX1632/MAX1635)
______________________________________________________________________________________ 25
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
_____________________________________________________________Application Circuits (continued)
ON/OFF
*
*
INPUT
+6V TO +24V
5V ALWAYS ON
C3
10Ω
0.1μF
22 23
5
21
4.7μF
V+ SHDN SECFB VL
4.7μF
18
16
25
27
BST5
BST3
0.1μF
Q1
DH5
DH3
Q3
0.1μF
R1
L1
0.1μF
0.1μF
2.5V OUTPUT
26
24
17
19
L2
R2
LX5
DL5
LX3
DL3
+3.3V OUTPUT
C2
Q2
*
Q4
MAX1631
MAX1634
C1
*
20
14
1N5819
1N5819
PGND
CSH5
1
2
CSH3
CSL3
13
CSL5
0Ω
OPEN
12
3
FB3
FB5
RESET OUTPUT
11
10
0Ω
OPEN
RESET
SKIP
7
TIME/ON5
RUN/ON3
GND
ON/OFF
ON/OFF
28
4
STEER
8
REF SYNC SEQ
15
9
6
1μF
R1 = R2 = 15mΩ
L1 = L2 = 6.8μH SUMIDA CDRH 127-6R8MC
Q1 = Q4 = Si4410DY or 1RF7413
C1 = C2 = 2X SANYO OS-CON 10 SA220M
C3 = 4X SANYO OS-CON 30SC10M
*VL DIODES AND OUTPUT SCHOTTKY DIODES REQUIRED
FOR THE MAX1631 ONLY (SEE OUTPUT OVERVOLTAGE PROTECTION
AND OUTPUT UNDERVOLTAGE SHUTDOWN PROTECTION SECTIONS).
Figure 10. Dual, 4A, Notebook Computer Power Supply
26 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
________________________________________________________________________________Pin Configurations
TOP VIEW
CSH3
CSL3
CSH3
CSL3
FB3
28
27
26
25
24
28
27
26
25
1
2
1
2
RUN/ON3
DH3
RUN/ON3
DH3
LX3
LX3
FB3
STEER
SECFB
SYNC
3
3
BST3
DL3
BST3
4
12OUT
4
V
24 DL3
5
5
DD
MAX1631
MAX1634
MAX1630
MAX1632
MAX1633
MAX1635
6
SHDN
SYNC
6
23 SHDN
23
22
21
20
19
18
17
TIME/ON5
V+
VL
TIME/ON5
GND
7
7
22
21
20
19
18
17
16
15
V+
VL
8
GND
REF
8
9
9
REF
PGND
DL5
PGND
DL5
10
10
SKIP
SKIP
RESET 11
RESET 11
BST5
LX5
BST5
LX5
12
13
14
12
13
14
FB5
FB5
16
15
CSL5
CSH5
DH5
SEQ
CSL5
CSH5
DH5
SEQ
SSOP
SSOP
_______________________________________________________________Selector Guide
OVER/UNDERVOLTAGE
DEVICE
AUXILIARY OUTPUT
SECONDARY FEEDBACK
PROTECTION
MAX1630
MAX1631
MAX1632
MAX1633
MAX1634
MAX1635
12V Linear Regulator
None (SECFB input)
12V Linear Regulator
12V Linear Regulator
None (SECFB input)
12V Linear Regulator
Feeds into the 3.3V SMPS
Selectable (STEER pin)
Feeds into the 5V SMPS
Feeds into the 3.3V SMPS
Selectable (STEER pin)
Feeds into the 5V SMPS
Yes
Yes
Yes
No
No
No
______________________________________________________________________________________ 27
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
__Ordering Information (continued)
PART
TEMP RANGE
0°C to +70°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
28 SSOP
MAX1631CAI
MAX1631CAI+
MAX1631EAI+
MAX1632CAI
MAX1632CAI+
MAX1632EAI+
MAX1633CAI
MAX1633CAI+
MAX1633EAI+
MAX1634CAI
MAX1634CAI+
MAX1634EAI+
MAX1635CAI
MAX1635CAI+
MAX1635EAI+
+ Denotes lead-free package.
28 ______________________________________________________________________________________
Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
2
1
INCHES
MILLIMETERS
DIM
A
MIN
0.068
MAX
MIN
1.73
0.05
0.25
0.09
MAX
1.99
0.21
0.38
0.20
INCHES
MIN
MAX
MILLIMETERS
MIN
6.07
6.07
7.07
8.07
MAX
6.33
N
0.078
A1
B
D
D
D
D
D
0.239 0.249
0.239 0.249
0.278 0.289
0.317 0.328
14L
0.002 0.008
0.010 0.015
0.004 0.008
6.33 16L
7.33
8.33 24L
20L
C
E
H
D
SEE VARIATIONS
0.205 0.212 5.20
0.0256 BSC
0.397 0.407 10.07 10.33 28L
E
5.38
e
0.65 BSC
H
0.301 0.311 7.65
0.025 0.037 0.63
7.90
0.95
8∞
L
0∞
8∞
0∞
N
A
C
B
L
e
A1
D
NOTES:
1. D&E DO NOT INCLUDE MOLD FLASH.
2. MOLD FLASH OR PROTRUSIONS NOT TO EXCEED .15 MM (.006").
3. CONTROLLING DIMENSION: MILLIMETERS.
4. MEETS JEDEC MO150.
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, SSOP, 5.3 MM
APPROVAL
DOCUMENT CONTROL NO.
REV.
5. LEADS TO BE COPLANAR WITHIN 0.10 MM.
1
21-0056
C
1
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 29
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
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