AMC7635
APPLICATION INFORMATION
V
IN
V
IN
V
OUT
V
OUT
AMC7635
C
IN
1uF
BP
C
BP
1000pF
GND
EN
C
OUT
2.2uF
GND
Detailed Description
The AMC7635 CMOS low dropout regulator contains a PMOS pass transistor, a voltage reference, an error
amplifier, over-current protection, and thermal shutdown circuit.
The P-channel pass transistor receives data from the error amplifier, over-current shutdown, and thermal
protection circuits. During normal operation, the error amplifier compares the output voltage to a precision
reference. T hermal shutdown and over-current circuits become active when the junction temperature exceeds
150℃, or the current exceeds 300mA. During thermal shutdown, the output voltage remains low. Normal operation
is restored when the junction temperature drops below 120℃.
External Capacitors
The AMC7635 is stable with an output capacitor to ground of 2.2µF or greater. Ceramic capacitors have the
lowest ESR, and will offer the best AC performance. Conversely, Aluminum Electrolytic capacitors exhibit the
highest ESR, resulting in the poorest AC response. Unfortunately, large value ceramic capacitors are comparatively
expensive. One option is to parallel a 0.1µF ceramic capacitor with a 10µF Aluminum Electrolytic. The benefit is
low ESR, high capacitance, and low over-all cost.
A second capacitor is recommended between the input and ground to stabilize V
IN
. The input capacitor should be
at least 0.1µF to have a beneficial effect.
A third capacitor can be connected between the BP pin and GND. This capacitor can be a low cost Polyester
Film variety between the value of 0.001 ~ 0.01µF. A larger capacitor improves the AC ripple rejection, but also
makes the output come up slowly. This "Soft" turn-on is desirable in some applications to limit turn-on surges.
All capacitors should be placed in close proximity to the pins. A "Quiet" ground termination is desirable. This
can be achieved with a "Star" connection.
EN
The EN pin is normally pulled to high. When shutdown, pulled low, the PMOS pass transistor shuts off, and
all internal circuits are powered down. In this state, the quiescent current is less than 1µA. This pin behaves much
like an electronic switch.
Copyright
©
2007 ADDtek Corp.
7
DD078_A
-- SEPTEMBER 2007
ADDTEK [ ADDTEK CORP ]
