AN30185A
14
Ver. BEB
• UVLO function
When power supply rises to 2.6 V or higher at EN = High, UVLO is released, and the operation of each
function starts.
Since this function's hysteresis is 100 mV, UVLO detects when power supply falls to 2.5 V or lower,
then each
function shuts down.
• Reset function
RESET pin shifts to High at 30 ms delay after power supply rises to 2.92 V or higher.
(Output type : Nch MOS open drain)
Since this function's hysteresis is 110 mV, RESET pin shifts to Low when power supply falls to
2.81 V or lower.(No delay in case of High → Low)
• DC-DC1 (Output voltage : 1.0 V)
When UVLO is released, DC-DC1 starts and outputs 1.0 V. Soft-start function operates for 1 ms after startup.
Since output voltage rises slowly, limiting input current, it is possible to prevent rush current and overshoot.
When UVLO detects, DC-DC1 turns off. When EN pin shifts to Low, an output pin (FB1) is terminated
with a resistor.
• External Pch-MOSFET gate control function
PCNT pin is discharged by the constant current (2.5 μA) at 0.94 ms delay after UVLO is released.
By connecting the gate of Pch MOSFET to PCNT pin, it is possible to turn on this FET softly.
At the same time, the termination with a resistor of DIS pin is released.
Just after UVLO detects, PCNT pin voltage becomes V
IN
and DIS pin is terminated with a resistor.
• DC-DC2 (Output voltage : 1.8 V)
When both EN pin and EN2 pin are fixed to High, DC-DC2 turns on and outputs 1.8 V. Start-up timing
is as follows.
1) In case that EN pin becomes Low → High when EN2 pin is fixed to High
→ 3.75 ms delay from UVLO release
2) In case that EN2 pin becomes Low → High within 3.75 ms from UVLO release when EN pin
is fixed to High
→ 3.75 ms delay from UVLO release
3) In case that EN2 pin becomes Low → High after 3.75 ms from UVLO release when EN pin
is fixed to High
→ 1.88 ms to 3.76 ms delay from when EN2 pin becomes Low → High
DC-DC2 has the same soft-start function as DC-DC1 and starts, preventing rush current and overshoot.
DC-DC2 stops because UVLO detects. When EN pin shifts to Low, an output pin (FB2) is terminated
with a resistor.
DC-DC2 also stops when EN2 pin becomes Low, and the output pin is terminated with a resistor.
• BUF (Output voltage : 0.9 V)
BUF pin outputs 0.9 V when both EN pin and EN2 pin are fixed to High. Start-up timing is 0.47 ms delay
after DC-DC2
turns on. BUF starts, preventing rush current and overshoot.
BUF stops because UVLO detects. BUF is terminated with a resistor when EN pin shifts to Low.
BUF also stops when EN2 pin becomes Low, and the output pin is terminated with a resistor.
OPERATION (Continued)
3. Protection
Note) The characteristics listed below are reference values derived from the design of the IC and are not guaranteed.
