MIC24045 datasheet(28/46 Pages) MICROCHIP

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MIC24045

DS20005568A-page 28

 2016 Microchip Technology Inc.

7.0

APPLICATION INFORMATION

7.1

Programming External UVLO

The EN pin can be used to program an automatic

turn-on of the MIC24045 when the VIN (or VINLDO)

power rails have exceeded a desired threshold. This

programmable UVLO function

is achieved

described in Figure 7-1.

FIGURE 7-1:

Programmable External

UVLO Function.

The programmed VIN UVLO threshold VIN_RISE is

given by:

EQUATION 7-1:

To desensitize the VIN UVLO threshold against varia-

tions of the pull-up current EN_I, it is recommended to

run the R1-R2 voltage divider at a significantly higher

current level than the EN_I current.

The corresponding VIN UVLO hysteresis, VIN_HYS, is

calculated as follows:

EQUATION 7-2:

7.2

Output Voltage Sensing

To achieve accurate output voltage regulation, the

OUTSNS pin (internal feedback divider top terminal)

should be Kelvin-connected as close as possible to the

point-of-regulation top terminal. Since both the internal

reference and the internal feedback divider’s bottom

terminal refer to AGND, it is important to minimize

voltage

drops

between

the

AGND and the

point-of-regulation return terminal.

7.3

VOUT On-The-Fly Changes

It is possible to change the output voltage on-the-fly

during power delivery by writing a different value to

possible only within each VOUT range, as specified in

the VOUT selection table in Register 5-4.

The transition from one particular VOUT value to

another is under control of the I2C interface. The num-

ber of steps from one code to another and the speed of

the transition are left to the end user.

Single Write instructions separated by a Repeated

START (Sr) can be used to update Register 5-4 multi-

ple subsequent times, without releasing the I2C bus.

Please refer to section Section 8.5.2 “Single Write

with Repeated Start (Sr)”

for more details.

The minimum tSU_STA specification (set-up time for a

repeated START condition), the SCL frequency and the

length of the Single Write message (3 bytes) dictate a

limitation on the maximum update rate of the VOUT

code at Register 5-4.

Ramping down the output voltage at no or light load

implies inductor current reversal (i.e., the MIC24045

will be sinking current from the output capacitor). The

larger the output capacitor value, the larger the reverse

inductor current will be for a given negative VOUT vari-

ation.The voltage steps and the ramping step rate

should be small enough to maintain a safe level of

reverse current magnitude. This is especially important

when using large output capacitors.

7.4

Inductor Selection and Slope

Compensation

When selecting an inductor, it is important to consider

the following factors:

• Inductance

• Rated Current value

• Size requirements

• DC Resistance (DCR)

• Core losses

Enable

Comparator

EN_I

2 µA

AGND

EN_R

1.21V

VINLDO

Enable

Power

Delivery

135 mV

VIN

IN_RISE

EN_R

-------





EN_I



where:

EN_R

= 1.21V

EN_I

= 2 µA

RI, R2

= External resistors

IN_HYS

135 mV

-------







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