Pam3112, Application information – Diodes PAM3112 User Manual
Page 7
PAM3112
Document number: DSxxxxx Rev. 2 - 3
7 of 17
January 2013
© Diodes Incorporated
PAM3112
A Product Line of
Diodes Incorporated
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
startup time.
Load Transient Consideration
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 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 V
IN
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 batterypowered 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:
(
)
I
*
V
I
*
V
V
P
GND
IN
O
OUT
IN
D
+
−
=
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:
(
)
θ
−
=
JA
A
)
MAX
(
J
)
MAX
(
D
/
T
T
P