APPLICATION NOTES
Definition of Terms
Typical application circuit (adjustable output)
Dropout Voltage: The input-output voltage differential at which
the circuit stops to regulate against further reduction in input
voltage. Measured when the output voltage has dropped 100mV
from the nominal voltage obtained at 1V input, dropout voltage is
dependent upon load current and junction temperature.
Input Voltage: The DC voltage applied to the input terminal with
respect to ground.
VIN
100k
OUT
VOUT
OFF
ON/OFF
AMS3102
ADJUSTABLE
R1
28k
Input-Output Differential: The voltage difference between the
unregulated input voltage and the regulated output voltage for
which the regulator will regulate.
10µ
F
+
ADJ
ON
C1
22
µ
F
GND
R2
Line Regulation: The change in output voltage for a change in
the input voltage. The line regulation is measured under conditions
of low dissipation or by using low duty cycle pulse testing such
that the average chip temperature is not significantly affected.
Load Regulation: The change in output voltage for a change in
load current at constant chip temperature.
Minimum Load
Long term stability: Output voltage stability under accelerated
life-test conditions after 1000 hours with maximum rated voltage
and junction temperature.
In circuits using the fixed output voltage versions, minimum load
is not required. For circuits using the adjustable device, the value
of R1 and R2 should be chosen such, that a current of
approximately 40µA flows through the network. The reference
Output Noise Voltage: The rms AC voltage at the output, with
constant load and no input ripple, measured over a specified
frequency range.
voltage (1.235V) is measured between the adjust pin and VOUT
.
Quiescent Current: That part of the positive input current that
does not contribute to the positive load current. The regulator
ground lead current.
The output voltage can be set by the two resistors R1 and R2
using the following equation:
Ripple Rejection: The ratio of the peak-to –peak input ripple
voltage to the peak-to-peak output ripple voltage at specified
frequency.
R1+ R2
VO = VREF
R1
Temperature Stability of VO: The percentage change in output
voltage for a thermal variation from room temperature to either
temperature extreme.
The value of R1 is recommended to be between 25kΩ to 30 kΩ,
and the value of R2 will set the output voltage.
External capacitor
The AMS3102 series require an output capacitor of 2.2µF or
greater to ensure device stability. Without the capacitor the device
may oscillate.
Most type of tantalum or electrolytic capacitor can be used in the
applications. A critical characteristic of the capacitors is an ESR
value of 5Ω or less and a resonant frequency above 500kHz. The
value of this capacitor can be increased without limits.
For higher loads, the value of the capacitor should be increased,
specially when the output voltage is set for 2.5V or less. The
AMS3102 lowest fixed output voltage value is 2.0V.
Advanced Monolithic Systems http://www.ams-semitech.com
AMS [ Advanced Monolithic Systems Ltd ]
