R1224N Datasheet, PDF (13/42 Pages) RICOH electronics devices division – PWM/VFM step-down DC/DC Converter

TIMING CHART
VIN
VOUT Set Output Voltage
UVLO Voltage
Input Voltage
Rising Time
CE
UVLO Reset
VOUT Set Output Voltage
Protection Circuit Delay Time
R1224N
VOUT Set Output
Voltage
EXT
VOUT Set Output
Voltage
VOUT
Stable
Operation
Reset Protection
Stable
Operation
Stable
Operation
Soft Start
Soft Start Soft Start
Soft Start
The timing chart shown above describes the changing process of input voltage rising, stable operating,
operating with large current, stable operating, input voltage falling, input voltage recovering, and stable
operating.
First, until when the input voltage (VIN) reaches UVLO voltage, the circuit inside keeps the condition of
pre-standby.
Second, after VIN becomes beyond the UVLO threshold, soft-start operation starts, when the soft-start
operation finishes, the operation becomes stable.
If too large current flows through the circuit because of short or other reasons, EXT signal ignores that during
the delay time of protection circuit. (The current value depends on the circuit.)
After the delay time passes, reset protection works, or EXT signal will be “H”, then output will turn off, then
soft-start operation starts. After the soft-start operation, EXT signal will be “L”, but if the large current is still
flowing, after the delay time of protection circuit passes, reset protection circuit will work again, the operation will
be continuously repeated unless the cause of large current flowing is not removed.
Once the cause of the large current flowing is removed, within the delay time, the operation will be back to the
stable one.
If the timing for release the large current is in the protection process, the operation will be back to the normal
one after the soft-start operation.
If the VIN becomes lower than the set VOUT, that situation is same as large current condition, so protection
circuit may be ready to work, therefore, after the delay time of protection circuit, EXT will be “H”.
Further, if the VIN is lower than UVLO voltage, the circuit inside will be stopped by UVLO function.
After that, if VIN rises, until when the VIN reaches UVLO voltage, the circuit inside keeps the condition of
spre-standby.
Then after VIN becomes beyond the UVLO threshold, soft-start operation starts, when the soft-start operation
finishes, the operation becomes stable.
13