MIC33153 datasheet(13/28 Pages) MICROCHIP

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DS20006223B-page 13

MIC33153

4.0

FUNCTIONAL DESCRIPTION

4.1

VIN

The input supply (VIN) provides power to the internal

MOSFETs for the switch mode regulator along with the

internal control circuitry. The VIN operating range is

2.7V to 5.5V so an input capacitor, with a minimum

voltage rating of 6.3V, is recommended. Due to the high

switching speed, a minimum 2.2 µF bypass capacitor

placed close to VIN and the power ground (PGND) pin

is required.

4.2

A logic high signal on the enable pin activates the

output voltage of the device. A logic low signal on the

enable pin deactivates the output and reduces supply

current to 0.01 µA. MIC33153 features external

soft-start circuitry via the soft-start (SS) pin that

reduces in rush current and prevents the output voltage

from overshooting at start up. Do not leave the EN pin

floating.

4.3

The switch (SW) connects directly to one end of the

inductor and provides the current path during switching

cycles. The other end of the inductor is connected to

the load, SNS pin and output capacitor. Due to the high

speed switching on this pin, the switch node should be

routed away from sensitive nodes whenever possible.

4.4

SNS

The sense (SNS) pin is connected to the output of the

device to provide feedback to the control circuitry. The

SNS connection should be placed close to the output

capacitor.

4.5

AGND

The analog ground (AGND) is the ground path for the

biasing and control circuitry. The current loop for the

signal ground should be separate from the power

ground (PGND) loop.

4.6

PGND

The power ground pin is the ground path for the high

current in PWM mode. The current loop for the power

ground should be as small as possible and separate

from the analog ground (AGND) loop as applicable.

4.7

Power Good (PG)

The Power Good (PG) pin is an open-drain output that

indicates logic high when the output voltage is typically

above 92% of its steady state voltage. When the output

voltage is below 86%, the PG pin indicates logic low. A

pull up resistor of more than 10 kΩ should be

connected from PG to VOUT.

4.8

Soft-Start

The soft-start (SS) pin is used to control the output

voltage ramp up time. The approximate equation for

the ramp time in milliseconds is:

EQUATION 4-1:

For example, for a CSS = 470 pF, TRISE ~ 0.3 ms or

300 µs. See Section 2.0, Typical Performance Curves

for a graphical guide. The minimum recommended

value for CSS is 100 pF.

4.9

The feedback (FB) pin is provided for the adjustable

voltage option (no internal connection for fixed

options). This is the control input for programming the

output voltage. A resistor divider network is connected

to this pin from the output and is compared to the

internal 0.62V reference within the regulation loop.

The output voltage can be programmed between 0.65V

and 3.6V using the following equation:

EQUATION 4-2:

tSS 270 10

3 ln 10

 

CSS



Where:

tSS =

Soft-start ramp up time of VOUT

CSS = External soft-start capacitance (in Farads)

VOUT VREF 1 R1

-------









Where:

R1 =

Top resistor

R2 =

Bottom resistor

VREF =

0.62V

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