Rainbow Electronics MAX783 User Manual

RDY5

19-0045; Rev 1; 5/94

Evaluation Kit

Information Included

Triple-Output Power-Supply Controller

for Notebook Computers

_______________General Description

The MAX783 is a system-engineered power-supply controller
for notebook computers or similar battery-powered equipment.
It provides two high-performance step-down (buck) pulse­width modulators (PWMs) for +3.3V/+5V and dual PCMCIA
VPP outputs powered by an integral flyback winding controller.
Other functions include dual, low-dropout, micropower linear
regulators for CMOS/RTC back up, and two precision low­battery-detection comparators.

High efficiency (95% at 2A, greater than 80% at loads from
5mA to 3A) is achieved through synchronous rectification
and PWM operation at heavy loads, and Idle-Mode

TM

oper­ation at light loads. The MAX783 uses physically small
components, thanks to high operating frequencies
(300kHz/200kHz) and a new current-mode PWM architec­ture that allows for output filter capacitors as small as 30µF
per ampere of load. Line- and load-transient responses
are terrific, with a high 60kHz unity-gain crossover frequen­cy that allows output transients to be corrected within four
or five clock cycles. Low system cost is achieved through
a high level of integration and the use of low-cost external
N-channel MOSFETs. The integral flyback winding con­troller provides a low-cost, +15V high-side output that regu­lates even in the absence of a load on the main output.

Other features include low-noise, fixed-frequency PWM
operation at moderate to heavy loads and a synchronizable
oscillator for noise-sensitive applications such as electro­magnetic pen-based systems and communicating comput­ers. The MAX783 is similar to the MAX782, except the fly­back winding is on the 3.3V inductor instead of the 5V
inductor, the VPP outputs can be optionally programmed to

3.3V, and the device may be completely shut down.

________________________Applications

Notebook Computers
Portable Data Terminals
Communicating Computers
Pen-Entry Systems

_______Typical Application Diagram

+3.3V

+5V

µP
MEMORY
PERIPHERALS

DUAL

PCMCIA

SLOTS

5.5V
TO

30V

VPP



CONTROL

ON3

ON5
SYNC
SHDN

™

Idle-Mode is a trademark of Maxim Integrated Products. Pentium is a trademark of Intel. PowerPC is a trademark of IBM.

MAX783

4

POWER

SECTION

SUSPEND POWER

LOW-BATTERY WARNING

VPP (0V/3.3V/5V/12V)
VPP (0V/3.3V/5V/12V)

________________________________________________________________

Call toll free 1-800-998-8800 for free samples or literature.

____________________________Features

♦ Dual PWM Buck Controllers (+3.3V and +5V)
♦ Dual PCMCIA VPP Outputs (0V/3.3V/5V/12V)
♦ Two Precision Comparators or Level Translators
♦ Power-Ready Status Output (
♦ 95% Efficiency

)

♦ Optimized for 6-Cell Applications
♦ 420µA Quiescent Current;

70µA in Standby (linear regulators alive)
25µA Shutdown Current

♦ 5.5V to 30V Input Range
♦ Small SSOP Package
♦ Fixed Output Voltages Available:

3.3V (standard)

3.45V (High-Speed Pentium™)

3.6V (PowerPC™)

______________Ordering Information

PIN-PACKAGETEMP. RANGEPART

36 SSOP0°C to +70°CMAX783CBX
36 SSOP0°C to +70°CMAX783RCBX

Ordering Information continued on last page.

__________________Pin Configuration

TOP VIEW

ON3

SHDN

RDY5
VPPA

VDD

VPPB

GND

REF

SYNC

DA1
DA0
DB1

DB0

1
2

D1

3

D2

4

VH

5

Q2

6
7

Q1

MAX783

8

9
10
11
12
13
14
15
16
17
18

36

SS3
CS3

35

FB3

34

DH3

33

LX3

32
31

BST3

30

DL3

29

V+

28

VL

27

FB5

26

PGND

25

DL5

24

BST5

23

LX5

22

DH5

21

CS5

20

SS5

19

ON5

SSOP

Maxim Integrated Products

V

OUT

3.3V

3.45V

MAX783

1

Triple-Output Power-Supply Controller
for Notebook Computers

ABSOLUTE MAXIMUM RATINGS

V+ to GND.................................................................-0.3V, +36V

PGND to GND........................................................................±2V

VL to GND ...................................................................-0.3V, +7V

BST3, BST5 to GND ..................................................-0.3V, +36V

LX3 to BST3.................................................................-7V, +0.3V

LX5 to BST5.................................................................-7V, +0.3V

Inputs/Outputs to GND

MAX783

(D1, D2, S—H—D—N–, ON5, REF, SYNC, DA1, DA0, DB1, DB0, ON5,

SS5, CS5, FB5, R—D—Y—5–, CS3, FB3, SS3, ON3).-0.3V, (VL + 0.3V)

VDD to GND.................................................................-0.3V, 20V

VPPA, VPPB to GND.....................................-0.3V, (VDD + 0.3V)

VH to GND...................................................................-0.3V, 20V

Q1, Q2 to GND................................................-0.3V, (VH + 0.3V)

DL3, DL5 to PGND..........................................-0.3V , (VL + 0.3V)

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, GND = PGND = 0V, IVL= I
T

= T

to T

A

MIN

3.3V AND 5V STEP-DOWN CONTROLLERS

Input Supply Range
FB5 Output Voltage

FB3 Output Voltage

Line Regulation

Current-Limit Voltage

15V FLYBACK CONTROLLER

VDD Regulation Setpoint

VDD Shunt Setpoint

VDD Shunt Current

Quiescent VDD Current

PCMCIA REGULATORS (Note 1)

VPPA/VPPB Output Voltage

, unless otherwise noted.)

MAX

PARAMETER

0mV < (CS5-FB5) < 70mV, 6V < V + < 30V
(includes load and line regulation)

0mV < (CS3-FB3) < 70mV, 6V < V + < 30V
(includes load and line regulation)

Either controller (0mV to 70mV)
Either controller (6V to 30V)
CS3-FB3 or CS5-FB5
CS3-FB3 (VDD < 13V, flyback mode)

Falling edge, hysteresis = 1%
Rising edge, hysteresis = 1%
VDD = 20V
VDD = 18V, ON3 = ON5 = 5V, VPPA/VPPB programmed to

12V with no external load
VDD = 18V, ON3 = ON5 = 5V, VPPA/VPPB programmed to

0V

Program to 12V, 13V < VDD < 19V, 0mA < IL< 60mA
Program to 5V, 13V < VDD < 19V, 0mA < IL< 60mA
Program to 3.3V, 13V < VDD < 19V, 0mA < IL< 60mA
Program to 0V, 13V < VDD < 19V, 0mA < IL< 0.3mA

= 0mA, S—H—D—N–= ON3 = ON5 = 5V, other digital input levels are 0V or +5V,

REF

CONDITIONS

DH3 to LX3..................................................-0.3V, (BST3 + 0.3V)

DH5 to LX5..................................................-0.3V, (BST5 + 0.3V)

REF, VL, VPP Short to GND........................................Momentary

REF Current.........................................................................20mA

VL Current...........................................................................50mA

VPPA, VPPB Current.........................................................100mA

Continuous Power Dissipation (TA= +70°C)

SSOP (derate 11.76mW/°C above +70°C) ...................762mW

Operating Temperature Ranges:

MAX783CBX/MAX783_CBX.................................0°C to +70°C

MAX783EBX/MAX783_EBX ..............................-40°C to +85°C

Storage Temperature Range.............................-65°C to +160°C

Lead Temperature (soldering, 10sec).............................+300°C

UNITS

MAX783
MAX783R
MAX783S

MIN TYP MAX

3.17 3.35 3.46

3.32 3.50 3.60

3.46 3.65 3.75

2.5Load Regulation

80 100 120

-50 -100 -160

2SS3/SS5 Fault Sink Current

13 14
18 20

140 300

11.60 12.10 12.50

4.85 5.05 5.20

3.17 3.30 3.43

-0.30 0.30

V5.5 30
V4.80 5.08 5.20

V

%

%/V0.03

mV

µA2.5 4.0 6.5SS3/SS5 Source Current

mA

V
V

mA23

µA

µA15 30Off VDD Current

V

2 _______________________________________________________________________________________

Triple-Output Power-Supply Controller

for Notebook Computers

ELECTRICAL CHARACTERISTICS (continued)

(V+ = 15V, GND = PGND = 0V, IVL= I
T

= T

to T

A

MIN

INTERNAL REGULATOR AND REFERENCE

VL Output Voltage
VL Fault Lockout Voltage

VL/FB5 Switchover Voltage
(also R—D—Y—5–Trip Voltage)

REF Output Voltage 3.24 3.36µAV
REF Fault Lockout Voltage
REF Load Regulation 30 75 mV

Shutdown V+ Current

Standby V+ Current
Quiescent Power Consumption

(both controllers on)
Off V+ Current

COMPARATORS

D1, D2 Trip Voltage
D1, D2 Input Current
Q1, Q2 R—D—Y—5–Source Current
Q1, Q2 R—D—Y—5–Sink Current
Q1, Q2, R—D—Y—5–Output High Voltage

Q1, Q2, R—D—Y—5–Output Low Voltage
Quiescent VH Current

OSCILLATOR AND INPUTS/OUTPUTS

Oscillator Frequency
SYNC High Pulse Width 200 ns

SYNC Low Pulse Width 200 ns
SYNC Rise/Fall Time
Oscillator SYNC Range

Maximum Duty Cycle
Input Low Voltage 0.8

Input High Voltage
Input Current

, unless otherwise noted.)

MAX

PARAMETER

ON5 = ON3 = 0V, 5.5V < V+ < 30V, 0mA < IL< 25mA
Falling edge, hysteresis = 1%

Rising edge of FB5, hysteresis = 1%
No external load (Note 2)

Falling edge
0mA < IL< 5mA (Note 3)

–S—H—D—N–
DB1 = 0V, V+ = 30V

D1 = D2 = ON3 = ON5 = DA0 = DA1 = DB0 = DB1 = 0V,
V+ = 30V

D1 = D2 = D3 = DA0 = DA1 = DB0 = DB1 = 0V,
FB5 = CS5 = 5.25V, FB3 = CS3 = 3.5V

FB5 = CS5 = 5.25V, VL switched over to FB5

Falling edge, hysteresis = 1%
D1 = D2 = 0V to 5V
VH = 15V, V
VH = 15V, V
I

SOURCE

I

SINK

VH = 18V, D1 = D2 = 5V, no external load

SYNC = 3.3V
SYNC = 0V or 5V

SYNC = 3.3V
SYNC = 0V or 5V
S—H—D—N–, ON3, ON5, DA0, DA1, DB0, DB1, SYNC

S—H—D—N–, ON3, ON5, DA0, DA1, DB0, DB1
SYNC
S—H—D—N–, ON3, ON5, DA0, DA1, DB0, DB1, VIN= 0V or 5V

= 0mA, S—H—D—N–= ON3 = ON5 = 5V, other digital input levels are 0V or +5V,

REF

CONDITIONS

= D1 = D2 = ON3 = ON5 = DA0 = DA1 = DB0 =

= 2.5V

OUT

2.5V

OUT

= 5µA, VH = 3V

= 20µA, VH = 3V

MIN TYP MAX

4.5 5.5 V

3.6 4.2 V

4.2 4.7 V

2.4 3.2 V

25 40

70 110 µA

5.2 8.6
30 60

1.61 1.69
±100 nA

12 20 30 µA

200 500 1000%µA

VH - 0.5 V

0.4 V

410µA

270 300 330
170 200 230

200 nsNot tested

240 350

89 92
92 95

2.4

VL - 0.5

±1 µA

MAX783

UNITS

µA

mW

V

kHz

kHz

V
V

_______________________________________________________________________________________ 3

Triple-Output Power-Supply Controller
for Notebook Computers

ELECTRICAL CHARACTERISTICS (continued)

(V+ = 15V, GND = PGND = 0V, IVL= I
T

= T

to T

A

MIN

, unless otherwise noted.)

MAX

PARAMETER

DL3/DL5 Sink/Source Current V

OUT

DH3/DH5 Sink/Source Current BST3-LX3 = BST5-LX5 = 4.5V, V

MAX783

DL3/DL5 On-Resistance High or low 7 Ω
DH3/DH5 On-Resistance High or low, BST3-LX3 = BST5-LX5 = 4.5V 7 Ω

Note 1: Output current is further limited by maximum allowable package power dissipation.
Note 2: Because the reference uses VL as its supply, the REF line regulation error is insignificant.
Note 3: The main switching outputs track the reference voltage. Loading the reference reduces the main outputs slightly according

to the closed-loop gain (AV
AVCLfor the +5V supply is 1.54.

) and the reference voltage load regulation error. AVCLfor the +3.3V supply is unity gain.

CL

__________________________________________Typical Operating Characteristics

(Circuit of Figure 1, Transpower TTI5902 transformer, TA = +25°C, unless otherwise noted.)

= 0mA, S—H—D—N–= ON3 = ON5 = 5V, other digital input levels are 0V or +5V,

REF

CONDITIONS UNITS

MIN TYP MAX

= 2V 1 A

= 2V 1 A

OUT

100

90

80

70

EFFICIENCY (%)

60

50

1m

EFFICIENCY vs.

+5V OUTPUT CURRENT

V+ = 6V

V+ = 15V

N1-N4 = IRF7101
ON3 = LOW
F = 200kHz

10m 1

100m

+5V OUTPUT CURRENT (A)

QUIESCENT SUPPLY CURRENT vs.

SUPPLY VOLTAGE

14

13

ON3 = ON5 = HIGH

2

1

QUIESCENT SUPPLY CURRENT (mA)

0

0 6 12 18 24 30

SUPPLY VOLTAGE (V)

MAX183 5

10

100

90

80

70

EFFICIENCY (%)

60

50

1m

EFFICIENCY vs.

+3.3V OUTPUT CURRENT

V+ = 6V

V+ = 15V

N1-N4 = IRF7101
ON3 = ON5 = HIGH
F = 200kHz

10m 1

+3.3V OUTPUT CURRENT (A)

100m

MAXIMUM +15V VDD OUTPUT CURRENT vs.

500

MAX183 6

400

300

200

100

MAXIMUM +15V LOAD CURRENT (mA)

10

2.5

2.0

1.5

1.0

0.5

STANDBY SUPPLY CURRENT (mA)

0

0 6 12 18 24 30

0

STANDBY SUPPLY CURRENT vs.

SUPPLY VOLTAGE

ON3 = ON5 = 0V

SUPPLY VOLTAGE (V)

SUPPLY VOLTAGE

>

VDD

+13V

+3.3V REGULATING

+3.3V LOAD = 0A

05 20

+3.3V LOAD = 3A

10 15

SUPPLY VOLTAGE (V)

4 _______________________________________________________________________________________

Triple-Output Power-Supply Controller

for Notebook Computers

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 1, Transpower TTI5902 transformer, TA = +25°C, unless otherwise noted.)

SHUTDOWN SUPPLY CURRENT vs.

SUPPLY VOLTAGE

500

400

300

200

100

SHUTDOWN SUPPLY CURRENT (µA)

0

SHDN = 0V

0

612182430

SUPPLY VOLTAGE (V)

PULSE-WIDTH MODULATION MODE WAVEFORMS

MINIMUM VIN TO V

vs. +5V OUTPUT CURRENT

1.0

0.8

0.6

DIFFERENTIAL (V)

OUT

0.4

TO V

IN

0.2

MINIMUM V

0

1m 10m 100m 1 10

+5V OUTPUT CURRENT (A)

LX VOLTAGE
10V/div

+5V OUTPUT
VOLTAGE
50mV/div

DIFFERENTIAL

OUT

300kHz

+5V OUTPUT
STILL REGULATING

200kHz

SWITCHING FREQUENCY (kHz)

IDLE-MODE WAVEFORMS

SWITCHING FREQUENCY vs.

1000

100

10

1

0.1
100µ 10m 1

LOAD CURRENT

SYNC = REF (300kHz)
ON3 = ON5 = HIGH

+5V, VIN = 7.5V

+5V, VIN = 30V

1m 100m

LOAD CURRENT (A)

+3.3V, VIN = 7.5V

+5V OUTPUT
50mV/div

2V/div

MAX783


I
V

LOAD

IN

= 1A

= 16V

500ns/div


I

LOAD

V

IN

= 10V

= 100mA

200µs/div

_______________________________________________________________________________________

5

Triple-Output Power-Supply Controller
for Notebook Computers

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 1, Transpower TTI5902 transformer, TA = +25°C, unless otherwise noted.)

+5V LOAD-TRANSIENT RESPONSE

MAX783


V

= 15V

IN

)

30

VIN = 10V

RMS

20

V

OUT

I

10

OUT



0

-10

-20

-30

OUTPUT VOLTAGE NOISE (dBmV



1

200µs/div



OUTPUT NOISE SPECTRUM

= 5V

= 50mA



10 100

FREQUENCY (kHz)

3A

LOAD CURRENT

0A

+5V OUTPUT
50mV/div


I

LOAD

+5V LINE-TRANSIENT RESPONSE, FALLING


I

LOAD

= 2A

20µs/div

)

RMS

OUTPUT VOLTAGE NOISE (dBmV

+5V LINE-TRANSIENT RESPONSE, RISING

20µs/div

= 2A

+5V OUTPUT
50mV/div

VIN, 16V TO 10V
2V/div





100k 1M

FREQUENCY (Hz)



30

VIN = 8V TO 12V

20

(PLOTS SUPERIMPOSED)

10

= 5V

V

OUT

0

= 1A

I

OUT



-10

-20

-30

-40

-50

-60


10k

OUTPUT NOISE SPECTRUM

+5V OUTPUT
50mV/div

VIN, 10V TO 16V
2V/div

6 _______________________________________________________________________________________

Triple-Output Power-Supply Controller

for Notebook Computers

______________________________________________________________Pin Description

PIN

15-18

NAME FUNCTION

1 ON3 ON/O—F—F–control input to disable the +3.3V PWM. Tie directly to VL for automatic start-up.

Shutdown control input, low-true logic. Tie to VL for automatic start-up. The 5V VL supply stays active in

2 S—H—D—N

3 D1
4 D2 #2 level-translator/comparator noninverting input (see D1).

5 VH External positive supply voltage input for the level translators/comparators and R—D—Y—5–output.
6 Q2
7 Q1 #1 level translator/comparator output (see Q2).
8 R—D—Y—5

9 VPPA 0V, 3.3V, 5V, 12V switchable PCMCIA VPP output. Sources 60mA. Controlled by DA0 and DA1.
10 VDD
11 VPPB 0V, 3.3V, 5V, 12V switchable PCMCIA VPP output. Sources 60mA. Controlled by DB0 and DB1.

12 GND Low-current analog ground. Feedback reference point for all outputs.
13 REF

14 SYNC

19 ON5 ON/O—F—F–control input to disable the +5V PWM supply. Tie to VL for automatic start-up.
20 SS5 Soft-start control input for +5V. Ramp time to full current limit is 1ms/nF of capacitance to GND.
21 CS5 Current-sense input for +5V. Current limit level is +100mV referred to FB5.
22 DH5 Gate-drive output for the +5V high-side MOSFET.
23 LX5 Inductor connection for the +5V supply.
24 BST5 Boost capacitor connection for the +5V supply (0.1µF).
25 DL5 Gate-drive output for the +5V low-side MOSFET.
26 PGND Power ground
27 FB5 Feedback and current-sense input for the +5V PWM.
28 VL 5V logic supply voltage for internal circuitry. VL is always on and can source 5mA for external loads.
29 V+ Supply voltage input from battery, 5.5V to 30V
30 DL3 Gate-drive output for the +3.3V low-side MOSFET.
31 BST3 Boost capacitor connection for the +3.3V supply (0.1µF).
32 LX3 Inductor connection for the +3.3V supply.
33 DH3 Gate-drive output for the +3.3V high-side MOSFET.
34 FB3 Feedback and current-sense input for the +3.3V PWM.
35 CS3 Current-sense input for +3.3V, current limit level is +100mV referred to FB3.
36 SS3 Soft-start input for +3.3V. Ramp time to full current limit is 1ms/nF of capacitance to GND.

–

–

DA1, DA0,
DB1, DB0

shutdown. Don't force S—H—D—N–higher than VL + 0.5V.
#1 level-translator/comparator noninverting input, threshold = +1.650V. Controls Q1. Tie to GND if

unused.

#2 level-translator/comparator output. Sources 20µA from VH when D2 is high. Sinks 500µA to GND when
D2 is low, even with VH = 0V.

Power-good indication for the main +5V supply. Low indicates greater than 4.5V at the +5V output.
Swings 0V to VH.

+15V flyback input (feedback). A weak shunt regulator conducts 3mA to GND when VDD exceeds 19V.
VDD serves as the supply input for the VPP linear regulators.

3.3V reference output sources up to 5mA for external loads. Bypass to GND with 1µF/mA of load or

0.22µF minimum
Oscillator control/synchronization input. Connect to VL or GND for 200kHz; connect to REF for 300kHz.

For external clock synchronization in the 240kHz to 350kHz range, a high-to-low transition starts a new cycle.
PCMCIA digital control inputs with industry-standard coding (see Table 1).

MAX783

_______________________________________________________________________________________ 7

Triple-Output Power-Supply Controller
for Notebook Computers

Table 1. Truth Table for VPP Control Pins

D_0 D_1 VPP

0 0 0V
0 1 5V
1 0 12V

MAX783

1 1 3.3V

_______________Detailed Description

The MAX783 converts a 5.5V to 30V input to six outputs
(Figure 1). It produces two high-power, PWM switch­mode supplies, one at +5V and the other at +3.3V. The
two supplies operate at either 300kHz or 200kHz, allow­ing for small external components. Output current capa­bility depends on external components, and can exceed
6A on each supply. Two 12V VPP outputs, an internal 5V,
25mA supply (VL) and a 3.3V, 5mA reference voltage
are also generated via linear regulators (Figure 2). Fault­protection circuitry shuts off the PWM and high-side sup­ply when the internal supplies lose regulation.

Two precision voltage comparators are also included.
Their output stages permit them to be used as level
translators for driving external N-channel MOSFETs in
load-switching applications, or for more conventional
logic signals.

The MAX783 is capable of accepting input voltages
from 5.5V to 30V, but is optimized for the lower end of
this range because the +15V flyback winding controller
is appended to the +3.3V buck supply. This architecture
allows for lower input voltages than are possible with the
MAX782 sister chip, which puts the winding on the +5V
side, while maintaining high +15V load capability.
However, the MAX783’s transformer has a higher turns
ratio (4:1 vs. 2:1), which leads to higher interwinding
capacitance as well as higher switching noise ampli­tudes at the transformer secondary when the input volt­age is high. Therefore, the MAX783 standard applica­tion circuit is optimized with external components for
low-voltage (6-8 cell) designs with maximum input volt­ages of 20V and less. The MAX783 itself can easily
accept 30V inputs, but expect to see more noise and
higher voltage swings at the transformer secondary
under these conditions. The inductor and filter capacitor
values may also require some adjustment for inputs
greater than 20V; see the

The +5V supply is generated by a current-mode PWM
step-down regulator using two N-channel MOSFETs, a
rectifier, plus an LC output filter (Figure 1). The gate­drive signal to the high-side MOSFET, which must
exceed the battery voltage, is provided by a boost cir-

Design Procedure

section.

+5V Switch-Mode Supply

cuit that uses a 100nF capacitor connected to BST5.
The +5V supply’s dropout voltage, as configured in
Figure 1, is typically 400mV at 2A. As V+ approaches
5V, the +5V output falls with V+ until the VL regulator
output hits its undervoltage lockout threshold at 4V. At
this point, the +5V supply turns off.

A synchronous rectifier at LX5 keeps efficiency high by
effectively clamping the voltage across the rectifier
diode. Maximum current limit is set by an external low­value sense resistor, which prevents excessive inductor
current during start-up or under short-circuit conditions.
Programmable soft-start is set by an optional external
capacitor; this reduces in-rush surge currents upon
start-up and provides adjustable power-up times for
power-supply sequencing purposes.

+3.3V Switch-Mode Supply

The +3.3V output is produced by a current-mode PWM
step-down regulator similar to the +5V supply. The +3.3V
supply uses a transformer primary winding as its induc­tor; the secondary is used for the 15V VDD supply.

The default switching frequency for both PWM controllers
is 200kHz (with SYNC connected to GND or VL), but
300kHz may be used by connecting SYNC to REF.

+3.3V and +5V PWM Buck Controllers

The two current-mode PWM buck controllers are nearly
identical except for different preset output voltages and
the addition of a flyback winding control loop to the

3.3V side. Each PWM is independent, except both are
synchronized to a master oscillator and share a com­mon reference (REF) and logic supply (VL). Each PWM
can be turned on and off separately via ON3 and ON5.
The PWMs are a direct-summing type, lacking a tradi­tional integrator-type error amplifier and the phase shift
associated with it. They therefore do not require exter­nal feedback compensation components if you follow
the filter capacitor ESR guidelines in the

Procedure

The main gain block is an open-loop comparator that
sums four input signals: output voltage error signal,
current-sense signal, slope-compensation ramp, and
precision reference voltage. This direct-summing
method approaches the ideal of cycle-by-cycle control
of the output voltage. Under heavy loads, the controller
operates in full PWM mode. Every pulse from the oscil­lator sets the output latch and turns on the high-side
switch for a period determined by the duty factor
(approximately V
off, the synchronous rectifier latch is set; 60ns later, the
low-side switch turns on. The low-side switch stays on
until the beginning of the next clock cycle (in continu­ous mode) or until the inductor current crosses through

.

). As the high-side switch turns

OUT/VIN

Design

8 _______________________________________________________________________________________

Triple-Output Power-Supply Controller

for Notebook Computers

MAX783

BATTERY INPUT

5.5V TO 30V
(NOTE 1)

VPP

CONTROL

INPUTS

+5V 

at 
3A

C3

330µF

+3.3V ON/OFF

+5V ON/OFF

SHUTDOWN

5V POWERGOOD

C1–C6 = SPRAGUE 595D or AVX TPS SERIES
N1–N4 = Si9410DY or IRF7101 (BOTH SECTIONS)
D1A, D1B = LOW-POWER SCHOTTKY (CMPSH3 OR EQUIVALENT)
FOR V

NOTE 1: BATTERY VOLTAGE RANGE 6V to 20V WITH COMPONENTS SHOWN.
NOTE 2: KEEP KELVIN-CONNECTED CURRENT-SENSE TRACES SHORT AND CLOSE TOGETHER. SEE FIG.5.
NOTE 3: ZENER DIODE CLAMP REQUIRED FOR VIN

R1

25mΩ

C4

330µF

+ < 6V. FOR V+ > 6V, 1N4148 OR EQUIVALENT IS ACCEPTABLE.

L1

10µH

1N5819

C1
33µF

D1A

C10

0.1µF

N1

D2

(NOTE 2)

N2

C13

0.01µF

> 12V. ZENER CAN BE REPLACED WITH 20kΩ PULL-DOWN OR OTHER 1mA MINIMUM LOAD.

16
15
18
17

24
22
23

25
21
27

20

1

19

2
8

29 28

V+ VL

DA1
DB0

DB1

MAX783

BST5
DH5
LX5
DL5

CS5
FB5

SS5

ON3

ON5

SHDN
RDY5

VPPADA0

VPPB

VDD

BST3

DH3

LX3
DL3

CS3

FB3
SS3

D1-D2
Q1-Q2

SYNC

REF

GNDPGND

1226

9

11

10

31
33
32

30
35

34
36
5

VH

3, 4
7, 6
14
13

D1B

C11

0.1µF

C14

0.01µF

C15
1µF

C7

4.7µF
C8

1µF

C9
1µF

2
2

N4

(NOTE 2)

N3

D3

EC11FS1

1:4

L2 10µH

D5
1N5819

+5V at 5mA

0V, 3.3V, 5V, 12V

0V, 3.3V, 5V, 12V
+15V AT 200mA, SEE 

HIGH-SIDE SUPPLY (VDD)

SECTION.

C12

2.2µF

R2

20mΩ

COMPARATOR SUPPLY INPUT
COMPARATOR INPUTS
COMPARATOR OUTPUTS
OSCILLATOR SYNC

3.3V AT 5mA

C2

33µF

D6
18V
100mW (NOTE 3)

+3.3V 

C5

C6

150µF

150µF



3A

at 

Figure 1. Standard Application Circuit

zero (in discontinuous mode). Under fault conditions
when the inductor current exceeds the 100mV current­limit threshold, the high-side latch resets and the high­side switch turns off.

At light loads, the inductor current fails to exceed the
25mV threshold set by the minimum current compara­tor. When this occurs, the PWM goes into idle mode,
skipping most of the oscillator pulses in order to reduce
the switching frequency and cut back switching losses.
The oscillator is effectively gated off at light loads
because the minimum current comparator immediately
resets the high-side latch at the beginning of each
cycle, unless the FB_ signal falls below the reference
voltage level.

_______________________________________________________________________________________ 9

A flyback winding controller regulates the +15V VDD
supply in the absence of a load on the main 3.3V out­put. If VDD falls below the preset +13V VDD regulation
threshold, a 1µs one-shot is triggered that extends the
low-side switch’s on-time beyond the point where the
inductor current crosses zero (in discontinuous mode).
This causes inductor (primary) current to reverse,
pulling current out of the output filter capacitor and
causing the flyback transformer to operate in the for­ward mode. The low impedance presented by the
transformer secondary in forward mode allows the
+15V filter capacitor to be quickly charged up again,
bringing VDD into regulation.