Pam3103, Application information – Diodes PAM3103 User Manual
Page 6
PAM3103
Document number: DSxxxxx Rev. 1 - 5
6 of 11
July 2013
© Diodes Incorporated
PAM3103
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 PAM3103 must be carefully selected for regulator stability and
performance.
A capacitor C
IN
of more than 1
μF 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>5m
Ω ensures stabilty.
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:
2
R
/
1
R
1
V
V
REF
O
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.
CC is unnecessary when R1
or R2 <20k
Ω. The recommended design procedure is to choose R2 =169kΩ to set the divider current at 7µA and then calculate R1 as below:
2
R
1
V
/
V
1
R
REF
O
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 V
IN
or leaving the EN input floating.
Internal P-Channel Pass Transistor
The PAM3103 features a 0.75
Ω device as a pass transistor. The PMOS 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 batterypowered 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.