MAX1626 Datasheet, PDF (6/16 Pages) Maxim Integrated Products – 5V/3.3V or Adjustable, 100% Duty-Cycle, High-Efficiency, Step-Down DC-DC Controllers

5V/3.3V or Adjustable, 100% Duty-Cycle,
High-Efficiency, Step-Down DC-DC Controllers
______________________________________________________________Pin Description
PIN
MAX1626 MAX1627
1
1
—
2
2
—
3
3
4
4
5
5
6
6
7
7
8
8
NAME
OUT
FB
3/5
SHDN
REF
V+
CS
EXT
GND
FUNCTION
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
INPUT
C2
68µF LOW-ESR
TANTALUM
C3
68µF LOW-ESR
TANTALUM
C5
0.47µF
C4
0.1µF
V+
MAX1626
3/5
RSENSE
0.04Ω
CS
U1
SHDN
EXT
REF _{GND OUT}
LOGIC-LEVEL MOSFET
P _L1
22µH, 3A
OUTPUT
C1
D1
220µF
LOW-ESR
TANTALUM
L1: SUMIDA CDRH125-220
D1: NIHON NSQ03A03
U1: MORTOLA MMSF3PO2HD
Figure 1. MAX1626 Typical Operating Circuit
EXT
REF
MAX1626
MAX1627
1.5V
MINIMUM ON-TIME
ONE-SHOT
Q
TRIG
ERROR
REF _COMPARATOR
R2
Q
TRIG
MINIMUM OFF-TIME
ONE-SHOT
R1
R3
Q
S
R
OUT
(FB)
3/5
SHDN
CURRENT-SENSE
COMPARATOR
Figure 2. Simplified Functional Diagram
V+
CS
( ) MAX1627 ONLY
MAX1626 ONLY
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