Rainbow Electronics MAX763A - Manual (Page 7)

MAX748A/MAX763A
3.3V, Step-Down,
Current-Mode PWM DC-DC Converters
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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