R1212D Datasheet, PDF (15/41 Pages) RICOH electronics devices division – STEP-UP DC/DC CONTOLLER

R1212D
<Latch Protection Operation>
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. The 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 supply voltage down to UVLO detector threshold or lower,
and make it rise up to the normal input voltage.
Once after becoming the maximum duty cycle, if the duty cycle decreases before latch operation works, the
charging the capacitor stops immediately, and the DELAY pin voltage is fixed at GND level with IDLY2.
The delay time of latch protection can be calculated with C2, VDLY, and the delay pin charge current, IDLY1, as in
the next formula.
t=C2 × VDLY/IDLY1
Output Short
DELAY
VDLY
AMPOUT
DTC
Normal
Maxduty Operation
Latched
EXT
IDLY1
VDLY
DELAY
C2
15