Pin Name Pin No. Type
ADJ 4 Input
4 Open drain
EN 3 Digital Input
1 Power in
5 Power out
Pin Function Description
FAN2508 Adjust. Ratio of potential divider from VOUT to ADJ
determines output voltage.
FAN2508-XX Bypass. Connect 470 pF capacitor for noise reduction.
FAN2509-XX Error. Error flag output.
0: Output voltage < 95% of nominal.
1: Output voltage > 95% of nominal.
0: Shutdown VOUT.
1: Enable VOUT.
Voltage Input. Supply voltage input.
Voltage Output. Regulated output voltage.
Designed utilizing CMOS process technology, the
FAN2508/09 family of products are carefully optimized for
use in compact battery-powered devices, offering a unique
combination of low power consumption, extremely low
dropout voltages, high tolerance for a variety of output
capacitors, and the ability to disable the output to less than
1µA under user control. In the circuit, a difference ampliﬁer
controls the current through a series-pass P-Channel
MOSFET, comparing the load voltage at the output with an
onboard low-drift bandgap reference. The series resistance
of the pass P-Channel MOSFET is approximately 1Ω,
resulting in an unusually low dropout voltage under load
when compared to older bipolar pass-transistor designs.
Protection circuitry is provided onboard for overload condi-
tions. In conditions where the device reaches temperatures
exceeding the speciﬁed maximums, an onboard circuit shuts
down the output, where it remains suspended until it has
cooled before re-enabling. The user is also free to shut down
the device using the Enable control pin at any time.
Careful design of the output regulator ampliﬁer assures loop
stability over a wide range of ESR values in the external
output capacitor. A wide range of values and types can be
accomodated, allowing the user to select a capacitor meeting
his space, cost, and performance requirements, and enjoy
reliable operation over temperature, load, and tolerance
2 REV. 1.0.6 2/14/03