R1211D103C datasheet(13/40 Pages) RICOH

13 / 40 page

R1211x

(Step3)

When SS reaches 1V, soft-start operation finishes. VREF becomes constant voltage (=1V). Then the switching

operation becomes normal mode.

VFB,VREF

DTC

AMPOUT

SS,VREF

Step1

Step2

Step3

VFB

VOUT

VIN

The operation of Latch protection circuit is as follows: When AMPOUT becomes "H" and the IC detects

maximum duty cycle, charge to an external capacitor, C2 of DELAY pin starts. And maximum duty cycle

continues and the voltage of DELAY pin reaches delay voltage detector threshold, VDLY, outputs "L" to EXT pin

and turns off the external power MOSFET.

To release the latch protection operation, make the IC be standby mode with CE pin and make it active in

terms of R1211x002B/D version. Otherwise, make supply voltage down to UVLO detector threshold or lower,

and make it rise up to the normal input voltage.

During the soft-start time, if the duty cycle may be the maximum, protection circuit does not work and DELAY

pin is fixed at GND level.

The delay time of latch protection can be calculated with C2, VDLY, and Delay Pin Charge Current, IDLY1, as in

the next formula.

t=C2

× VDLY/IDLY1

Once after the maximum duty is detected and released before delay time, charge to the capacitor is halt and

delay pin outputs "L".

AMPOUT

DTC

Output Short

Normal

Latched

Maxduty Operation

EXT

DELAY

VDLY

R1211D103C Datasheet(PDF) 13 Page - RICOH electronics devices division