PAM3103VOUTUBADJ datasheet(6/10 Pages) PAM

6 / 10 page

Capacitor Selection and Regulator Stability

ADJ Output Voltage Programming

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 PAM3103 must be

carefully selected for regulator stability and

performance.

Please note that the distance

between C

and the input pin of the PAM3103

should not exceed 0.5 inch. Ceramic capacitors are

suitable for the PAM3103. Capacitors with larger

values and lower ESR (equivalent series

resistance) provide better PSRR and line-transient

response.

The PAM3103 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 >

The output voltage of the PAM3103 adjustable

regulator is programed by using an external

resistor divider as shown in Figure1. The output

voltage is calculated as below:

V =V

(1+R1/R2)

Resistor R 1 and R2 should be chosen for

approximately 7 A divider current. Lower value

resistors can be used but offer no advantage and

waste more power. Higher value should be avoided

as leakage current at ADJ pin increase the output

voltage error.

V/V

- 1

C u r v e7o f

on page 5 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 PAM3103.

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 t o t he transient spike. A larger

capacitance along with smaller ESR results in a

smaller spike.

The PAM3103 can be shut down by pulling the

EN input low, and turned on by tying the EN

input to VIN or leaving the EN input floating.

The PAM3103 features a 0.75

device as a pass transistor. The P-

MOS pass transistor enables the PAM3103 to

consume only 65 A of ground current during low

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

This feature increases the battery operation life

time.

A regulator's minimum input-output voltage

differential (or dropout voltage) determines the

lowest usable supply voltage. The PAM3103 has

a typical 300mV dropout voltage. In battery-

powered systems, this will determine the useful

end-of-life battery voltage.

The PAM3103 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 PAM3103 also has a built-in short circuit

current limit.

OREF

2.2μF with

ESR>5mΩ ensures stability.

Ω P-Channel

MOSFET

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 .

the PAM3103 load-transient

response

is unnecessary when R1 or R2

<20k . The recommended design procedure is to

choose R2=169k

to set the divider current at 7 A

and then calculate R1 as below:

R1=(

)R2

Ωμ

Application Information

09/2008 Rev 1.2

Power Analog Microelectronics Inc

www.poweranalog.com

PAM3103

300mA Adjustable High PSRR CMOS Linear Regulator

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