User Manual

MAX782
Triple-Output Power-Supply
Controller for Notebook Computers
_______________________________________________________________________________________ 9
+3.3V Supply
The +3.3V supply is produced by a current-mode PWM
step-down regulator using two small N-channel MOSFETs,
a catch diode, an inductor, and a filter capacitor.
Efficiency is greatly enhanced by the use of the second
MOSFET (connected from LX3 to PGND), which acts as
a synchronous rectifier. A 100nF capacitor connected
to BST3 provides the drive voltage for the high-side
(upper) N-channel MOSFET.
A current limit set by an external sense resistor prevents
excessive inductor current during start-up or under
short-circuit conditions. A soft-start capacitor can be
chosen to tailor the rate at which the output ramps up.
This supply can be turned on by connecting ON3 to
logic high, or can be turned off by connecting ON3 to
GND. All logic levels are TTL and CMOS compatible.
+5V Supply
The +5V output is produced by a current-mode PWM
step-down regulator similar to the +3.3V supply. This
supply uses a transformer primary as its inductor, the
secondary of which is used for the high-side (VDD)
supply. It also has current limiting and soft-start. It can
be turned off by connecting ON5 to GND, or turned on
by connecting ON5 to logic high.
The +5V supply’s dropout voltage, as configured in
Figure 1, is typically 400mV at 2A. As V
IN
approaches
5V, the +5V output gracefully falls with V
IN
until the VL
regulator output hits its undervoltage lockout threshold.
At this point, the +5V supply turns off.
The default frequency for both PWM controllers is
300kHz (with SYNC connected to REF), but 200kHz
may be used by connecting SYNC to GND or VL.
VPPADA0
DA1
DB0
DB1
BST3
DH3
LX3
DL3
CS3
FB3
SS3
ON3
ON5
SYNC
VPPB
VDD
BST5
DH5
LX5
DL5
CS5
FB5
SS5
VH
D1-D3
Q1-Q3
9
11
10
24
22
23
25
21
27
20
5
2, 3, 4
8, 7, 6
16
15
18
17
31
33
32
30
35
34
36
1
19
14
GND REF PGND
29 28
12 13 26
BATTERY INPUT
5.5V TO 30V
(NOTE 1)
VPP
CONTROL
INPUTS
C1
33µF
D1A
1N4148
C5
N1
L1
10µH
R1
25mΩ
+3.3V at 3A
C14
150µF
C7
150µF
D3
1N5819
N3
C9
0.01µF
+3.3V ON/OFF
+5V ON/OFF
OSC SYNC
C3
1µF
C2
4.7µF
C11
1µF
C10
1µF
D1B
1N4148
C4
0.1µF
D2
EC11FS1
N2
1:2.2
L2 10µH
D4
1N5819
N4
R2
20mΩ
C12
2.2µF
C6
330µF
+5V at 3A
C8
0.01µF
3
3
COMPARATOR SUPPLY INPUT
COMPARATOR INPUTS
COMPARATOR OUTPUTS
3.3V AT 5mA
+5V at 5mA
0V, 5V, 12V
+15V AT 300mA, SEE 
HIGH-SIDE SUPPLY (VDD) 
SECTION.
0V, 5V, 12V
MAX782
V+ VL
C13
33µF
N1-N4 = Si9410DY
NOTE 1: BATTERY VOLTAGE RANGE 6.5V to 30V 
WITH COMPONENTS SHOWN
SEE
LOW-VOLTAGE (6-CELL) OPERATION SECTION.
NOTE 2: SEE FIGURE 5.
(NOTE 2)
(NOTE 2)
0.1µF
Figure 1. MAX782 Application Circuit