PAM3112 Datasheet, PDF (7/16 Pages) Power Analog Micoelectronics – 300mA CMOS Linear Regulator

PAM3112
300mA CMOS Linear Regulator
Application Information
Capacitor Selection and Regulator Stability
Similar to any low dropout regulator, the external
capacitors used with the PAM3112 must be
carefully selected for regulator stability and
performance.
A capacitor C_IN of more than 1μF can be used at
the PAM3112 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
PAM3112 should not exceed 0.5 inch. Ceramic
capacitors are suitable for the PAM3112.
Capacitors with larger values and lower ESR
(equivalent series resistance) provide better
PSRR and line-transient response.
The PAM3112 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.
A 10nF bypass capacitor connected to BYP pin is
suggested for suppressing output noise. The
capacitor, in series connection with an internal
200kΩ 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
Curve 7 of the PAM3112 load-transient response
on page 6 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 PAM3112. 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 is smaller spike.
Shutdown Input Operation
The PAM3112 is 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 PAM3112 features a 0.75Ω P-Channel
MOSFET device as a pass transistor. The P-MOS
pass transistor enables the PAM3112 to consume
only 65μA of ground current during low dropout,
light-load, or heavy-load operation. These
features increase 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 PAM3112 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 PAM3112 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
PAM3112 also has a built-in short circuit current
limit.
Thermal considerations
Thermal protection limits power dissipation in the
PAM3112. When the junction temperature
exceeds 150°C, the OTP (Over Temperature
Protection) starts the thermal shutdown and turns
the pass transistor off. The pass transistor
resumes operation after the junction temperature
drops below 120°C.
For continuous operation, the junction
temperature should be maintained below 125°C.
The power dissipation is defined as:
P_D= (V_IN-V ) _OUT *I_O+V *_IN I_GND
The maximum power dissipation depends on the
thermal resistance of IC package, PCB layout, the
rate of surrounding airflow and temperature
difference between junction and ambient. The
maximum power dissipation can be calculated by
the following formula:
P_D(MAX) = (T_J(MAX)-T_A)/θ_JA
Power Analog Microelectronics,Inc
www.poweranalog.com
7
10/2008 Rev 1.3