Rainbow Electronics MAX1627 - Manual (Page 6)

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