TC1302A_13 Datasheet, PDF (12/26 Pages) Microchip Technology – Low Quiescent Current Dual Output LDO

TC1302A/B
5.0 DETAILED DESCRIPTION
5.1 Device Overview
The TC1302A/B is a combination device consisting of
one 300 mA LDO regulator with a fixed output voltage
V_OUT1 (1.5V – 3.3V) and one 150 mA LDO regulator
with a fixed output voltage V_OUT2 (1.5V – 3.3V).
For the TC1302A, the 300 mA output (V_OUT1) is always
present, independent of the level of SHDN2. The
150 mA output (V_OUT2) can be turned ON/OFF by
controlling the level of SHDN2.
For the TC1302B, V_OUT1 and V_OUT2 each have
independent shutdown input pins (SHDN1 and
SHDN2) to control their respective outputs.
5.2 LDO Output #1
LDO output #1 is rated for 300 mA of output current.
The typical dropout voltage for V_OUT1 = 104 mV @
300 mA. A 1 µF (minimum) output capacitor is needed
for stability and should be located as close to the V_OUT1
pin and ground as possible.
5.3 LDO Output #2
LDO output #2 is rated for 150 mA of output current.
The typical dropout voltage for V_OUT2 = 150 mV. A 1 µF
(minimum) capacitor is needed for stability and should
be located as close to the V_OUT2 pin and ground as
possible.
5.4 Input Capacitor
Low input source impedance is necessary for the two
LDO outputs to operate properly. When operating from
batteries, or in applications with long lead length
(> 10 inches) between the input source and the LDO,
some input capacitance is recommended. A minimum
of 1.0 µF to 4.7 µF is recommended for most
applications. When using large capacitors on the LDO
outputs, larger capacitance is recommended on the
LDO input. The capacitor should be placed as close to
the input of the LDO as is practical. Larger input
capacitors will help reduce the input impedance and
further reduce any high-frequency noise on the input
and output of the LDO.
5.5 Output Capacitor
A minimum output capacitance of 1 µF for each of the
TC1302A/B LDO outputs is necessary for stability.
Ceramic capacitors are recommended because of their
size, cost and environmental robustness qualities.
Tantalum or aluminum electrolytic capacitors can be
used on the LDO outputs as well. The Equivalent
Series Resistance (ESR) requirements on the
electrolytic output capacitor’s are between 0 and 2
ohms. The output capacitor should be located as close
to the LDO output as is practical. Ceramic materials,
X7R and X5R, have low temperature coefficients and
are well within the acceptable ESR range required. A
typical 1 uF X5R 0805 capacitor has an ESR of 50 milli-
ohms. Larger LDO output capacitors can be used with
the TC1302A/B to improve dynamic performance and
power supply ripple rejection performance. A maximum
of 10 µF is recommended. Aluminum electrolytic
capacitors are not recommended for low temperature
applications of < -25 °C.
5.6 Bypass Input
The Bypass pin is connected to the internal LDO
reference. By adding capacitance to this pin, the LDO
ripple rejection, input voltage transient response and
output noise performance are all increased. A typical
bypass capacitor between 470 pF to 10 nF is
recommended. Larger bypass capacitors can be used,
but result in a longer time period for the LDO outputs to
reach their rated output voltage when started from
SHDN or V_IN.
5.7 GND
For the optimal noise and PSRR performance, the
GND pin of the TC1302A/B should be tied to a quiet
circuit ground. For applications that have switching or
noisy inputs, tie the GND pin to the return of the output
capacitor. Ground planes help lower inductance and
voltage spikes caused by fast transient load currents
and are recommended for applications that are
subjected to fast load transients.
5.8 SHDN1/SHDN2 Operation
The TC1302A SHDN2 pin is used to turn V_OUT2 ON
and OFF. A logic-high level on SHDN2 will enable the
V_OUT2 output, while a logic-low on the SHDN2 pin will
disable the V_OUT2 output. For the TC1302A, V_OUT1 is
not affected by SHDN2 and will be enabled as long as
the input voltage is present.
The TC1302B SHDN1 and SHDN2 pins are used to
turn V_OUT1 and V_OUT2 ON and OFF. They operate
independent of each other.
DS21333C-page 12
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