Table 1. typical soft-start times – Rainbow Electronics MAX763A User Manual
Page 7
MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
_______________________________________________________________________________________
7
SHDN
BIAS
GEN
OUT
CC
C5
330pF
1.23V
BANDGAP
ERROR AMP
C6
1000pF
REF
SS
1M
±35%
C1
0.047
µ
F
Σ
RAMP
GEN
SLOPE COMPENSATION
OVERCURRENT COMPARATOR
CURRENT
SENSE AMP
RSENSE
F/F
S
R
Q
PWM
COMPARATOR
SS CLAMP
200kHz
OSC
GND
VUVLO
UNDERVOLTAGE
LOCKOUT
D1
1N5817
C4
150
µ
F
VOUT
3.3V
L1
22
µ
H
LX
C2
1.0
µ
F
VIN
V+
C3
150
µ
F
MAX748A
MAX763A
MAX748A 3.3V to 16.0V
MAX763A 3.3V to 11.0V
Figure 1. Detailed Block Diagram with External Components
Circuit Cond.
Soft-Start Time (ms) vs. C1 (µF)
V+ (V) I
OUT
(mA) C1 = 0.01 C1 = 0.047 C1 = 0.1 C1 = 0.47
8
0
1
4
7
12
12*
0
1
2
3
6
8
200
10
33
50
200
12*
200
7
17
20
80
8
300
13
44
65
325
12*
300
8
25
35
140
* MAX748A only
Table 1. Typical Soft-Start Times
(Circuit of Figure 3, C4 = 150µF)
FROM SHDN
C1
SS
SS CLAMP
1M
±35%
1.23V
MAX748A
MAX763A
Figure 2. Soft-Start Circuitry Block Diagram