PAM3108 Datasheet, PDF (7/10 Pages) Power Analog Micoelectronics – Maximum 1.5A, Ultra Low Dropout Regulator

PAM3108
Maximum 1.5A, Ultra Low Dropout Regulator
Application Information
Capacitor Selection and Regulator Stability
Similar to any low dropout regulator, the external
capacitors used with the PAM3108 must be
carefully selected for regulator stability and
performance.
A capacitor C_IN of more than 10µF 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
PAM3108 should not exceed 0.5 inch. Ceramic
capacitors are suitable for the PAM3108.
Capacitors with larger values and lower ESR
(equivalent series resistance) provide better
PSRR and line-transient response.
The PAM3108 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
> 10µF with ESR>5mΩ ensures stability.
Shutdown Input Operation
The PAM3108 is shut down by pulling the EN
input low, and is turned on by tying the EN input to
CTRL or leaving the EN input floating.
Input-Output ( Dropout ) Voltage
A regulator's minimum input-output voltage
difference (or dropout voltage) determines the
lowest usable supply voltage. The PAM3108 has
a typical 150mV dropout voltage.
Current Limit and Short Circuit Protection
The PAM3108 features a current limit, which
monitors and controls the gate voltage of the
pass transistor. The output current can be limited
to 3A by regulating the gate voltage. The
PAM3108 also has a built-in short circuit current
limit.
Thermal considerations
Thermal protection limits power dissipation in the
PAM3108. When the junction temperature
exceeds 170°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 130°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
Where T_J(MAX) is the maximum allowable junction
t e m p e r a t u r e 1 2 5 °C , T _A i s t h e a m b i e n t
temperature and θ is the thermal resistance
JA
from the junction to the ambient.
Power Analog Microelectronics, Inc
www.poweranalog.com
7
07/2011 Rev1.0