Triple-Output Power-Supply
Controller for Notebook Computers
MAX782
BATTERY INPUT
5.5V TO 30V
(NOTE 1)
C1
33µF
16
VPP
CONTROL
INPUTS
15
18
17
D1A
1N4148
C5
0.1µF
+3.3V at 3A
R1
25mΩ
L1
10µH
D3
1N5819
N1
31
33
32
30
N3
35
DA0
DA1
DB0
DB1
VPPB
VDD
C13
33µF
29
V+
28
VL
VPPA
9
11
10
C2
4.7µF
C11
1µF
C10
1µF
D1B
1N4148 C4
0.1µF
N2
+5V at 5mA
0V, 5V, 12V
0V, 5V, 12V
D2
EC11FS1
+15V AT 300mA, SEE
HIGH-SIDE SUPPLY (VDD)
SECTION.
C12
2.2µF
+5V at 3A
MAX782
BST3
DH3
LX3
DL3
CS3
BST5
DH5
LX5
DL5
CS5
FB5
SS5
VH
D1-D3
Q1-Q3
REF PGND
13
26
24
22
23
25
21
27
20
5
2, 3, 4
8, 7, 6
1:2.2
L2 10µH
D4
1N5819
N4
R2
20mΩ
C14 C7
150µF 150µF
C6
330µF
(NOTE 2)
+3.3V ON/OFF
+5V ON/OFF
OSC SYNC
C9
0.01µF
34 FB3
36
SS3
1
ON3
19
ON5
14 SYNC
GND
12
C8
0.01µF
3
3
(NOTE 2)
COMPARATOR SUPPLY INPUT
COMPARATOR INPUTS
COMPARATOR OUTPUTS
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.
3.3V AT 5mA
C3
1µF
Figure 1. MAX782 Application Circuit
+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.
9
_______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
