XR79110

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exar.com/XR79110

Rev 2B

© 2015-2017 Exar Corporation

Programming the On-Time

ing to following equation:

where:

shown in figures 19, 21, 23

Over-Current Protection (OCP)

for four consecutive switching cycles, then Module enters

hiccup mode of operation. In hiccup, the MOSFET gates

are turned off for 110ms (hiccup timeout). Following the hic-

cup timeout, a soft-start is attempted. If OCP persists, hic-

cup timeout will repeat. The Module will remain in hiccup

mode until load current is reduced below the programmed

the following equation:

Where:

RDS is the MOSFET rated On Resistance (10mΩ)

8mV is the OCP comparator maximum offset

ILIM is the internal current that generates the necessary

OCP comparator threshold (use 45μA).

Note that ILIM has a positive temperature coefficient of

0.4%/°C (figure 9). This is meant to roughly match and

compensate for positive temperature coefficient of the syn-

in figure 7.

Short-Circuit Protection (SCP)

If the output voltage drops below 60% of its programmed

value, the Module will enter hiccup mode. Hiccup will per-

sist until short-circuit is removed. SCP circuit becomes

active after PGOOD asserts high.

Over-Temperature (OTP)

OTP triggers at a nominal die temperature of 150°C. The

gate of switching FET and synchronous FET are turned off.

When die temperature cools down to 135°C, soft-start is ini-

tiated and operation resumes.

Programming the Output Voltage

Use an external voltage divider as shown in the Application

where R2 has a nominal value of 2kΩ.

Programming the Soft-start

Place a capacitor CSS between the SS and AGND pins to

program the soft-start. In order to program a soft-start time

of TSS, calculate the required capacitance CSS from the

following equation:

R

ON

9

–

10



–





2.7

10

–

10

------------------------------------------------------------

=

T

ON





-------------------------------

=

R

ON

fEff



----------------





25

9

–

10

 V

IN





–

2.7

10

–

10

-------------------------------------------------------------------------

=

RLIM

RDS



 8mV

+

ILIM

------------------------------------------------------

=

R1

R2

0.6

-------------

1

–







=

CSS

TSS

10A

0.6V

--------------







=