3v supply, 5v supply – Rainbow Electronics MAX782 User Manual
Page 9
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.
VPPA
DA0
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
33
µ
F
D1A
1N4148
C5
N1
L1
10
µ
H
R1
25m
Ω
+3.3V at 3A
C14
150
µ
F
C7
150
µ
F
D3
1N5819
N3
C9
0.01
µ
F
+3.3V ON/OFF
+5V ON/OFF
OSC SYNC
C3
1
µ
F
C2
4.7
µ
F
C11
1
µ
F
C10
1
µ
F
D1B
1N4148 C4
0.1
µ
F
D2
EC11FS1
N2
1:2.2
L2 10
µ
H
D4
1N5819
N4
R2
20m
Ω
C12
2.2
µ
F
C6
330
µ
F
+5V at 3A
C8
0.01
µ
F
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
33
µ
F
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)
0.1
µ
F
Figure 1. MAX782 Application Circuit