PAM3101AAA310 datasheet(12/24 Pages) PAM

12 / 24 page

Capacitor Selection and Regulator Stability

Load Transient Considerations

Shutdown Input Operation

Internal P-Channel Pass Transistor

Input-Output ( Dropout ) Voltage

Current Limit and Short Circuit Protection

Similar to any low dropout regulator, the external

capacitors used with the PAM3101 must be

carefully selected for regulator stability and

performance.

A capacitor C of more than 1μF can be employed

in the input pin, while there is no upper limit for

the capacitance of C . Please note that the

distance between C

and the input pin of the

PAM3101 should not exceed 0.5 inch. Ceramic

capacitors a re suitable for t he PAM3101.

Capacitors with larger values and lower ESR

(equivalent series resistance) provide better

PSRR and line-transient response.

The PAM3101 is designed specifically to work

with low ESR ceramic output capacitors in order

to save space and improve performance. Using

an output ceramic capacitor whose value is

>μ

A 10nF bypass capacitor connected to BYP pin is

suggested for suppressing output noise. The

capacitor, in series connection with an internal

200k

resistor, forms a low-pass filter for noise

reduction. Increasing the capacitance will slightly

decrease the output noise, but increase the start-

up time.

Curve 10 of the PAM3101 load-transient

response on page 10 shows two components of

the output response: a DC shift from the output

impedance due to the load current change and

transient response. The DC shift is quite small

due to excellent load regulation of the PAM3101.

The transient spike, resulting from a step change

in the load current from 1mA to 300mA, is 20mV.

The ESR of the output capacitor is critical to the

transient spike. A larger capacitance along with

smaller ESR results in a smaller spike.

The PAM3101 is shut down by pulling the EN

input low, and is turned on by tying the EN input

to VIN or leaving the EN input floating.

The PAM3101 features a 0.75

device as a pass transistor. The P-

MOS pass transistor enables the PAM3101 to

consume only 65 A of ground current during low

dropout, light-load, or heavy-load operations.

This feature increases the battery operation life

time.

A regulator's minimum input-output voltage

difference (or dropout voltage) determines the

lowest usable supply voltage. The PAM3101 has

a typical 300mV dropout voltage. In battery-

powered systems, this will determine the useful

end-of-life battery voltage.

The PAM3101 features a current limit, which

monitors and controls the gate voltage of the

pass transistor. The output current can be

limited to 400mA by regulating the gate voltage.

The PAM3101 also has a built-in short circuit

current limit.

2.2 F with ESR>5mΩ ensures stability.

Ω P-Channel

MOSFET

Application Information

09/2008 Rev 1.4

Power Analog Microelectronics Inc

www.poweranalog.com

PAM3101

300mA High PSRR Low Dropout CMOS Linear Regulator

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