TC1302A datasheet(12/26 Pages) MICROCHIP

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TC1302A/B

DS21333B-page 12

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

VOUT1 (1.5V – 3.3V) and one 150 mA LDO regulator

with a fixed output voltage VOUT2 (1.5V – 3.3V).

For the TC1302A, the 300 mA output (VOUT1) is always

present, independent of the level of SHDN2. The

150 mA output (VOUT2) can be turned ON/OFF by

controlling the level of SHDN2.

For the TC1302B, VOUT1 and VOUT2 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 VOUT1 = 104 mV @

300 mA. A 1 µF (minimum) output capacitor is needed

for stability and should be located as close to the VOUT1

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 VOUT2 = 150mV. A 1µF

(minimum) capacitor is needed for stability and should

be located as close to the VOUT2 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

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

10 nF

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 VIN.

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 VOUT2 ON

and OFF. A logic-high level on SHDN2 will enable the

VOUT2 output, while a logic-low on the SHDN2 pin will

disable the VOUT2 output. For the TC1302A, VOUT1 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 VOUT1 and VOUT2 ON and OFF. They operate

independent of each other.

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