PAM3103 Datasheet, PDF (6/10 Pages) Power Analog Micoelectronics – 300mAAdjustable High PSRR CMOS Linear Regulator

PAM3103
300mA Adjustable High PSRR CMOS Linear Regulator
Application Information
Capacitor Selection and Regulator Stability
Similar to any low dropout regulator, the external
capacitors used with the PAM3103 must be
carefully selected for regulator stability and
performance.
A capacitor C_IN of more than 1μF can be employed
in the input pin, while there is no upper limit for the
capacitance of C ._IN Please note that the distance
between C_IN 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 >2.2μF with
ESR>5mΩ ensures stability.
ADJ Output Voltage Programming
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_O=V ( _REF 1+R1/R2)
Resistor R1 and R2 should be chosen for
approximately 7μA 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. C_C is unnecessary when R1 or R2
<20kΩ. The recommended design procedure is to
choose R2=169kΩ to set the divider current at 7μA
and then calculate R1 as below:
R1=(V_O/V_REF - 1)R2
Load Transient Considerations
Curve 7 of the PAM3103 load-transient
response 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 to the transient spike. A larger
capacitance along with smaller ESR results in a
smaller spike.
Shutdown Input Operation
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.
Internal P-Channel Pass Transistor
The PAM3103 features a 0.75Ω P-Channel
MOSFET device as a pass transistor. The P-
MOS pass transistor enables the PAM3103 to
consume only 65μA of ground current during low
dropout, light-load, or heavy-load operation.
This feature increases the battery operation life
time.
Input-Output (Dropout) Voltage
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.
Current Limit and Short Circuit Protection
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.
Power Analog Microelectronics,Inc
www.poweranalog.com
6
09/2008 Rev 1.2