ML4903
FUNCTIONAL DESCRIPTION
UNDERVOLTAGE LOCKOUT
The ML4903 has hysteretic undervoltage lockout
protection circuits for both the 12V (V
DD
) and 5V (V
CC
)
supplies. During an input undervoltage condition, the
internal reference and voltage monitor circuits remain in
operation, but P DRV and N DRV are disabled and the
PWR GOOD output will be false (low).
(Continued)
COMPENSATION
The COMP pin is connected to the output of the
transconductance amplifier which forms the gain block
for the proportional control loop of the ML4903. An RC
network from this pin to GND is used to compensate the
amplifier.
R6
10Ω
12VIN
C20
22µF
25V
C10
220nF
16V
L1
1µH
C12
220nF
16V
R3
1MΩ
R2
1kΩ
5VIN
VID0
VID1
VID2
VID3
VID4
OUTEN
1
2
3
4
5
6
7
PWRGD
C22
1nF
C14
220nF
16V
8
9
10
D0
D1
D2
D3
RANGE
SHDN
N/C
PWR GOOD
VREF
GND
U1
ML4903
PROTECT
VDD
VCC
P DRV
N DRV
PWR GND
N/C
COMP
ISENSE
VFB
20
19
18
17
16
15
14
13
12
11
R4
470kΩ
C13
1nF
C1
C11
220nF
16V
C2
C3
Q1, Q2
2X IRF7416
Q3, Q4
2X IRF7413
L2
5.6µH
VCCP
R1
33Ω
C4-C9
R5
100Ω
VSS
C1 - C3 - 820µF, 16V, Sanyo 16MV820GX
C4 - C9 - 1500µF, 6.3V, Sanyo 6MV1500GX
Figure 1. Typical VRM Circuit
6