5 V/3 .3 V o r Ad ju s t a b le , 1 0 0 % Du t y-Cyc le ,
Hig h -Effic ie n c y, S t e p -Do w n DC-DC Co n t ro lle rs
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
MAX1626
MAX1627
Sense input for fixed 5V or 3.3V output operation. OUT is internally connected to an
on-chip voltage divider (MAX1626). It does not supply current. Leave OUT uncon-
nected during adjustable-output operation (MAX1627).
1
1
OUT
Feedback Input for adjustable-output operation. Connect to an external voltage
divider between the output and GND (see the Setting the Output Voltage section).
—
2
2
FB
3.3V or 5V Selection. Output voltage is set to 3.3V when this pin is low or 5V when it
is high.
—
3/5
Active-High Shutdown Input. Device is placed in shutdown when SHDN is driven
high. In shutdown mode, the reference, output, and external MOSFET are turned off.
Connect to GND for normal operation.
3
3
SHDN
4
5
4
5
REF
V+
1.3V Reference Output. Can source 100µA. Bypass with 0.1µF.
Positive Supply Input. Bypass with 0.47µF.
/MAX1627
Current-Sense Input. Connect current-sense resistor between V+ and CS. External
MOSFET is turned off when the voltage across the resistor equals the current-limit
trip level (around 100mV).
6
6
CS
7
8
7
8
EXT
Gate Drive for External P-Channel MOSFET. EXT swings between V+ and GND.
Ground
GND
EXT
REF
ERROR
INPUT
C2
C3
1.5V
C5
0.47µF
68µF LOW-ESR
TANTALUM
68µF LOW-ESR
TANTALUM
REF
MAX1626
MAX1627
COMPARATOR
OUT
(FB)
MINIMUM ON-TIME
ONE-SHOT
R2
TRIG
Q
V+
Q
TRIG
R
0.04Ω
SENSE
R1
R3
MAX1626
GND
MINIMUM OFF-TIME
ONE-SHOT
3/5
CS
U1
3/5
LOGIC-LEVEL MOSFET
SHDN
EXT
P
L1
22µH, 3A
SHDN
Q
OUTPUT
S
R
REF
OUT
C1
C4
0.1µF
220µF
LOW-ESR
TANTALUM
D1
V+
CS
CURRENT-SENSE
COMPARATOR
L1: SUMIDA CDRH125-220
D1: NIHON NSQ03A03
U1: MORTOLA MMSF3PO2HD
( ) MAX1627 ONLY
MAX1626 ONLY
Figure 1. MAX1626 Typical Operating Circuit
Figure 2. Simplified Functional Diagram
6
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