FLF3215T-R47N datasheet(12/19 Pages) MICREL

12 / 19 page

Micrel, Inc.

MIC23163/4

July 29, 2013

Revision 2.0

Functional Description

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 2.2µF bypass capacitor

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

required. Refer to the “PCB Layout Recommendations”

section for details.

EN/Shutdown

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

0.1µA. When disabled the MIC23164 switches an internal

load of 180

Ω on the regulators switch node to discharge

the output. The MIC23163/4 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.

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.

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.

Refer

the

“PCB

Layout

Recommendations” section for details.

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. Refer to

the “PCB Layout Recommendations” section for details.

The power good (PG) pin is an open drain output which

indicates logic high when the output voltage is typically

above 90% of its steady state voltage. A pull-up resistor

of more than 5k

Ω should be connected from PG to V

OUT.

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

voltage ramp up time. The approximate equation for the

ramp time in seconds is 270 × 10

3 × ln(10) × C

SS. For

example, for a CSS = 1nF, TRISE ~ 600µs. The minimum

recommended value for CSS is 1nF.

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 0.7V

reference within the regulation loop.

The output voltage can be programmed between 0.7V

and VIN using Equation 1:











 +

REF

OUT

Eq. 1

where:

R1 is the top resistor, R2 is the bottom resistor.

Table 1. Example Feedback Resistor Values

VOUT

1.2V

215k

301k

1.5V

301k

261k

1.8V

340k

215k

2.5V

274k

107k

3.3V

383k

102k

3.6V

422k

102k

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