PAM3101
300mA High PSRR Low Dropout CMOS Linear Regulator
Application Information
Capacitor Selection and Regulator Stability
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
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
PAM3101 should not exceed 0.5 inch. Ceramic
c a p a c i t o r s a r e s u i t a b l e f o r t h e PA M 3 1 0 1 .
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
> 2.2 μ F with ESR>5mΩ ensures stability.
A 10nF bypass capacitor connected to BYP pin is
suggested for suppressing output noise. The
capacitor, in series connection with an internal
200k Ω resistor, forms a low-pass filter for noise
reduction. Increasing the capacitance will slightly
decrease the output noise, but increase the start-
up time.
Load Transient Considerations
C u r v e 1 0 o f t h e PA M 3 1 0 1 l o a d - t r a n s i e n t
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.
Shutdown Input Operation
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.
Internal P-Channel Pass Transistor
The PAM3101 features a 0.75 Ω P-Channel
MOSFET device as a pass transistor. The P-
MOS pass transistor enables the PAM3101 to
consume only 65 μ A of ground current during low
dropout, light-load, or heavy-load operations.
This feature increases the battery operation life
time.
Input-Output ( Dropout ) Voltage
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.
Current Limit and Short Circuit Protection
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.
Power Analog Microelectronics
,
Inc
www.poweranalog.com
09/2008 Rev 1.4
12
PAM [ POWER ANALOG MICOELECTRONICS ]
