Rainbow Electronics MAX773 - Manual (Page 10)

MAX770–MAX773
frequencies (up to 300kHz), allowing the use of tiny
external components.
As with traditional PFM converters, the power transistor
is not turned on until the voltage comparator senses
that the output is out of regulation. However, unlike tra-
ditional PFM converters, the MAX770–MAX773 switch
using the combination of a peak current limit and a pair
of one-shots that set the maximum on-time (16µs) and
minimum off-time (2.3µs); there is no oscillator. Once
off, the minimum off-time one-shot holds the switch
off for 2.3µs. After this minimum time, the switch either
1) stays off if the output is in regulation, or 2) turns on
again if the output is out of regulation.
The control circuitry allows the ICs to operate in contin-
uous-conduction mode (CCM) while maintaining high
efficiency with heavy loads. When the power switch is
5V/12V/15V or Adjustable, High-Efficiency,
Low I
Q , Step-Up DC-DC Controllers
10 ______________________________________________________________________________________
MAX770
V
IN
= 3V
REF
SHDN
FB
AGND
GND
N
7
EXT
CS
C2
0.1
µ F
C1
100 µ F
L1
22 µ H D1
1N5817
MTP3055EL
R SENSE
75m Ω
C4
300
µ F
C3
0.1 µ F
5
4
3
6
1
8
2
V+
V OUT = 5V
@ 1A
Figure 2a. 5V Preset Output, Bootstrapped Figure 2b. 12V Preset Output, Bootstrapped
Figure 2c. 12V Output, Non-Bootstrapped Figure 2d. 9V Output, Bootstrapped
MAX770
MAX771
MAX772
V
IN
= 5V
REF
SHDN
AGND
GND
N
7
EXT
CS
FB
L1
22 µ H
D1
1N5817
R1
18k
C4
200
µ F
C3
0.1 µ F
5
4
6
1
8
3
2
V+
C1
68 µ F
V OUT = 12V
@ 0.5A
R2
127k
R SENSE
100m Ω
C2
0.1
µ F
V OUT
V REF
R2 = (R1)
(
-1
)
V REF = 1.5V
MAX770
MAX771
MAX772
REF
SHDN
AGND
GND
N
7
EXT
CS
FB
C1
47 µ F L1
20 µ H
D1
1N5817
R1
28k
C4
100
µ F
C3
0.1 µ F
5
4
6
1
8
3
2
V+
V OUT = 9V
R2
140k
R
SENSE
C2
0.1
µ F
V
OUT
V REF
R2 = (R1)
(
-1
)
V REF = 1.5V
Si9410DY
V IN = 4V
MAX771
V
IN
= 5V
REF
SHDN
FB
AGND
GND
N
7
EXT
CS
C2
0.1
µ F
C1
68 µ F
L1
22 µ H D1
1N5817
Si9410DY
R SENSE
100m Ω
C4
200
µ F
C3
0.1 µ F
5
4
3
6
1
8
2
V+
V OUT = 12V
@ 0.5A