5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
MAX1626/MAX1627
______________________________________________________________Pin Description
PIN
NAME
MAX1626
1
MAX1627
1
OUT
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).
Feedback Input for adjustable-output operation. Connect to an external voltage
divider between the output and GND (see the
Setting the Output Voltage
section).
3.3V or 5V Selection. Output voltage is set to 3.3V when this pin is low or 5V when it
is high.
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.
1.3V Reference Output. Can source 100µA. Bypass with 0.1µF.
Positive Supply Input. Bypass with 0.47µF.
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).
Gate Drive for External P-Channel MOSFET. EXT swings between V+ and GND.
Ground
FUNCTION
—
2
2
—
FB
3/5
3
4
5
6
7
8
3
4
5
6
7
8
SHDN
REF
V+
CS
EXT
GND
INPUT
C2
68µF LOW-ESR
TANTALUM
C3
68µF LOW-ESR
TANTALUM
C5
0.47µF
1.5V
EXT
REF
REF
ERROR
COMPARATOR
OUT
R2
(FB)
R1
R3
3/5
SHDN
MAX1626
MAX1627
MINIMUM ON-TIME
ONE-SHOT
TRIG
Q
Q
TRIG
MINIMUM OFF-TIME
ONE-SHOT
V+
MAX1626
3/5
CS
SHDN
REF
C4
0.1µF
EXT
GND
OUT
D1
P
R
SENSE
0.04Ω
U1
LOGIC-LEVEL MOSFET
L1
22µH, 3A
OUTPUT
C1
220µF
LOW-ESR
TANTALUM
S
Q
R
CURRENT-SENSE
COMPARATOR
V+
CS
L1: SUMIDA CDRH125-220
D1: NIHON NSQ03A03
U1: MORTOLA MMSF3PO2HD
( ) MAX1627 ONLY
MAX1626 ONLY
Figure 1. MAX1626 Typical Operating Circuit
6
Figure 2. Simplified Functional Diagram
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