TC1301B-DAAVUATR Datasheet, PDF (14/28 Pages) Microchip Technology – Dual LDO with Microcontroller RESET Function

TC1301A/B
5.0 DETAILED DESCRIPTION
5.1 Device Overview
The TC1301A/B is a combination device consisting of
one 300 mA LDO regulator with a fixed output voltage,
V_OUT1 (1.5V – 3.3V), one 150 mA LDO regulator with a
fixed output voltage, V_OUT2 (1.5V – 3.3V), and a
microcontroller voltage monitor/RESET (2.2V to 3.2V).
For the TC1301A, 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 TC1301B, V_OUT1 and V_OUT2 each have
independent shutdown input pins (SHDN1 and
SHDN2) to control their respective outputs. In the case
of the TC1301B, the voltage detect input of the
microcontroller RESET function is internally connected
to the V_OUT1 output of the device.
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 RESET Output
The RESET output is used to detect whether the level
on the input of V_DET (TC1301A) or V_OUT1 (TC1301B) is
above or below a preset threshold. If the voltage
detected is below the preset threshold, the RESET
output is capable of sinking 1.2 mA (V_RESET < 0.2V
maximum). Once the voltage being monitored is above
the preset threshold, the RESET output pin will
transition from a logic-low to a logic-high after a 300 ms
delay. The RESET output is a push-pull configuration
and will actively pull the RESET output up to V_DET
when not in RESET.
5.5 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 applica-
tions. 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
DS21798C-page 14
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.
5.6 Output Capacitor
A minimum output capacitance of 1 µF for each of the
TC1301A/B LDO outputs is necessary for stability.
Ceramic capacitors are recommended because of their
size, cost and environmental robustness qualities.
Electrolytic (Tantalum or Aluminum) capacitors can be
used on the LDO outputs as well. The Equivalent
Series Resistance (ESR) requirements on the
electrolytic output capacitors 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 TC1301A/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.
5.7 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 results in a longer time-period for the LDO outputs
to reach their rated output voltage when started from
SHDN or V_IN.
5.8 GND
For the optimal noise and PSRR performance, the
GND pin of the TC1301A/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.
5.9 SHDN1/SHDN2 Operation
The TC1301A 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 TC1301A, V_OUT1 is
not affected by SHDN2 and will be enabled as long as
the input voltage is present.
The TC1301B SHDN1 and SHDN2 pins are used to
turn V_OUT1 and V_OUT2 ON and OFF. They operate
independent of each other.
© 2008 Microchip Technology Inc.