Dual-Output Power-Supply
Controller for Notebook Computers
MAX786
_________________Detailed Description
The MAX786 converts a 5.5V to 30V input to four outputs
(Figure 1). It produces two high-power, PWM, switch-
mode 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. An internal 5V, 5mA supply
(VL) and a 3.3V, 5mA reference voltage are also gener-
ated via linear regulators, as shown in Figure 2. Fault
protection circuitry shuts off the PWMs when the inter-
nal 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 MAX786 has two close relatives: the MAX782 and
the MAX783. The MAX782 and MAX783 each include
an extra flyback winding regulator and linear regulators
for dual, +12V/programmable PCMCIA VPP outputs.
The MAX782/MAX783 data sheet contains extra appli-
cations information on the MAX786 not found in this
data sheet.
+3.3V Switch-Mode Supply
The +3.3V supply is generated by a current-mode,
PWM step-down regulator using two N-channel
MOSFETs, a rectifier, and an LC output filter (Figure 1).
The gate-drive signal to the high-side MOSFET, which
must exceed the battery voltage, is provided by
a boost circuit that uses a 100nF capacitor connected
to BST3.
INPUT
5.5V TO 30V
(NOTE 1)
C1
33µF
D2A
1N4148
C5
0.1µF
25
27
26
LX3
24
V+
C10
33µF
23
VL
D2B
1N4148
C4
0.1µF
N2
4.7µF
22
+5V AT 5mA
BST3
DH3
BST5
DH5
LX5
18
16
17
+3.3V
AT
3A
R1
25mΩ
L1
10µH
N1
L2
10µH
R2
25m
+5V
AT
3A
C6
330µF
D1
1N5819
C7 C12
150µF 150µF
N3
DL3
DL5
19
N4
D3
1N5819
1
(NOTE 2)
C9
0.01µF
+3.3V ON/OFF
+5V ON/OFF
SHUTDOWN
OSC SYNC
MAX786
CS3
CS5
FB5
SS5
VH
D1
Q1
D2
Q2
15
21
14
6
4
8
5
7
(NOTE 2)
C8
0.01µF
COMPARATOR SUPPLY INPUT
IN
OUT
IN
OUT
COMPARATOR 2
COMPARATOR 1
28 FB3
2
3
13
12
11
SS3
ON3
ON5
SHDN
SYNC
NOTE 1: INPUT VOLTAGE RANGE 6.5V TO 30V
AS SHOWN. SEE
LOW-VOLTAGE
(6-CELL) OPERATION
SECTION FOR
DETAILS.
NOTE 2: USE SHORT, KELVIN-CONNECTED PC
BOARD TRACES PLACED VERY CLOSE
TO ONE ANOTHER.
GND
9
REF PGND
10
20
+3.3V AT 5mA
C3
1µF
Figure 1. MAX786 Application Circuit
8
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