Pam3108, Application information – Diodes PAM3108 User Manual
Page 7
PAM3108
Document number: DSxxxxx Rev. 1 - 0
7 of 11
www.diodes.com
October 2012
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PAM3108
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 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 ESR5>mΩ 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 junct ion 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:
(
)
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
Where T
J(MAX)
is the maximum allowable junction temperature +125°C, T
A
is the ambient temperature and is the thermal resistance from the
junction to the ambient.