5 V/3 .3 V o r Ad ju s t a b le , Hig h -Effic ie n c y,
Lo w -Dro p o u t , S t e p -Do w n DC-DC Co n t ro lle rs
49/MAX651
V+
FB
DUAL-MODE™
COMPARATOR
MAX1649
MAX1651
50mV
OUT
SHDN
REF
ERROR
COMPARATOR
1.5V
REFERENCE
N
MINIMUM
Q
OFF-TIME TRIG
ONE-SHOT
FROM V+
EXT
S
Q
F/F
MAXIMUM
TRIG ON-TIME
ONE-SHOT
Q
R
CURRENT
COMPARATOR
CS
110mV
FROM V+
GND
™ Dual-Mode is a trademark of Maxim Integrated Products
Figure 2. Block Diagram
S h u t d o w n Mo d e
When SHDN is high, the MAX1649/MAX1651 enter shut-
down mode. In this mode, the internal biasing circuitry is
turned off (including the reference) and the supply cur-
rent drops to less than 5µA. EXT goes high, turning off the
external MOSFET. SHDN is a logic-level input. Connect
SHDN to GND for normal operation.
Qu ie s c e n t Cu rre n t
In normal operation, the device's typical quiescent cur-
rent is 78µA. In an actual application, even with no load,
additional current is drawn to supply external feedback
resistors (if used) and the diode and capacitor leakage
currents. In the circuit of Figure 1, with V+ at 5V and
V
OUT
at 3.3V, typical no-load supply current for the
entire circuit is 90µA.
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7
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
