MIC5373 datasheet(14/19 Pages) MICREL

14 / 19 page

Micrel, Inc.

MIC5373/83

July 2010

M9999-070110

Pin Descriptions

INLDO

The LDO input pins INLDO1/2 and INLDO3 provide the

input power to the linear regulators LDO1, LDO2 and

LDO3. The input operating voltage range is from 1.7V to

5.5V. For input voltages from 1.7V to 2.5V the output

current must be limited to 30mA each. Due to line

inductance a 1µF capacitor placed close to the INLDO

pins and the GND pin is recommended. Please refer to

layout recommendations.

BIAS

The BIAS pin provides power to the internal reference

and control sections of the MIC5373/83. A 0.1µF

ceramic capacitor must be connected from BIAS to GND

for clean operation.

EN (MIC5373)

The enable pins EN1, EN2 and EN3 provide logic level

control for the outputs OUT1, OUT2 and OUT3,

respectively. A logic high signal on an enable pin

activates the respective LDO. A logic low signal on an

enable pin deactivates the respective LDO. Do not leave

the EN pins floating, as it would leave the regulator in an

unknown state.

/EN (MIC5383)

The enable pins /EN1, /EN2 and /EN3 provide logic level

control for the outputs OUT1, OUT2 and OUT3,

respectively. A logic high signal on an enable pin

deactivates the respective LDO. A logic low signal on an

enable pin activates the respective LDO. Do not leave

the EN pins floating, as it would leave the regulator in an

unknown state.

OUT

OUT1, OUT2 and OUT3 are the output pins of each

LDO. A minimum of 1µF capacitor be placed as close as

possible to each of the OUT pins. A minimum voltage

rating of 6.3V is recommended for each capacitor.

GND

The GND pin is the ground path for the control circuitry

and the power ground for all LDOs. The current loop for

the ground should be kept as short as possible. Refer to

the layout recommendations for more details.

POR

The POR (power-on-reset) pin is an open drain output. A

resistor (10kΩ to 100kΩ) can be used for a pull up to

either the input or the output voltage of the regulator.

POR is asserted high when the voltage at DLY reaches

1.25V. A delay can be added by placing a capacitor from

the DLY pin to ground.

POR_IN

The POR_IN (power-on-reset input) pin compares any

voltage to an internal 0.9V reference. This function can

be used to monitor any of the LDO outputs or any

external voltage rail. When the monitored voltage is

greater than 0.9V, the POR_IN flag will internally trigger

a 1.25µA source current to charge the external capacitor

at the DLY pin. A resistor divider network may be used

to divide down the monitored voltage to be compared

with the 0.9V at the POR_IN. This resistor network can

change the trigger point to any voltage level. A small

decoupling capacitor is recommended between POR_IN

and ground to reject high frequency noise that might

interfere with the POR circuit. Do not leave the POR_IN

pin floating.

DLY

The delay pin is used to set the POR delay time. Adding

a capacitor to this pin adjusts the delay of the POR

signal. When the POR_IN flag is triggered, a constant

1.25µA current begins to charge the external capacitor

tied to the DLY pin. When the capacitor reaches 1.25V

the POR will be pulled high by the external pull up

resistor. The equation to calculate the charge time is

shown:

⎟

⎠

⎞

⎜

⎝

⎛

−6

DLY

Delay

1.25V

(s)

The delay time (t) is in seconds, the delay voltage is

1.25V internally, and the external delay capacitance

(CDLY) is in microfarads. For a 1µF delay capacitor, the

delay time will be 1 second. A capacitor at the DLY pin is

recommended when the POR function is used in order to

prevent unexpected triggering of the POR signal in noisy

systems.

The MR (manual reset) pin resets the output of POR and

DLY generator regardless if the monitored voltage is in

regulation or not. Applying a voltage greater than 1.2V

on the MR pin will cause the POR voltage to be pulled

low. When a voltage below 0.2V is applied to the MR

pin, the internal 1.25µA will begin to charge the DLY pin

until it reaches 1.25V.

When the DLY pin reaches

1.25V, the POR voltage will be pulled high by the pull up

external resistor again. Do not leave the MR pin floating.

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