S-8363B-I6T1U2 Datasheet, PDF (14/50 Pages) Seiko Instruments Inc – PWM/PFM SWITCHABLE SWITCHING REGULATOR

STEP-UP, SUPER-SMALL PACKAGE, 1.2 MHz PWM/PFM SWITCHABLE SWITCHING REGULATOR
S-8363 Series
Rev.2.0_01
4. Power-off pin
This pin stops or starts step-up operations.
When the ON / OFF pin is set to the low level, the internal driver of the CONT pin is turned off and all internal circuits
stop substantially reducing the current consumption.
The ON / OFF pin is set up as shown in Figure 13 and is internally pulled down by using the depression transistor,
so all circuits stop even if this pin is floating. Do not apply a voltage of between 0.25 V and 0.75 V to
the ON / OFF pin because applying such a voltage increases the current consumption. If the ON / OFF pin is not used,
connect it to the VIN pin.
Table 8
ON/OFF pin
“H”
“L”
CR oscillation
circuit
Operates
Stops
Output voltage
Set value
VIN − VD
VIN
VIN
ON/OFF
VSS
Figure 13
5. Current limit circuit
A current limit circuit is built in the S-8363 Series.
The current limit circuit monitors the current that flows in the Nch power MOS FET and limits current in order to
prevent thermal destruction of the IC due to an overload or magnetic saturation of the inductor.
When a current exceeding the current limit detection value flows in the Nch power MOS FET, the current limit
circuit operates and turns off the Nch power MOS FET since the current limit detection until one clock of the
oscillator ends. The Nch power MOS FET is turned on in the next clock and the current limit circuit resumes
current detection operation. If the value of the current that flows in the Nch power MOS FET remains the current
limit detection value or more, the current limit circuit functions again and the same operation is repeated. Once
the value of the current that flows in the Nch power MOS FET is lowered up to the specified value, the normal
operation status restores.
The current limit detection value is fixed to 1.1 A (typ.) in the IC. However, under the condition that ON duty is
small, between the detection delay time of the current limit circuit and the ON time of the Nch power MOS FET,
the difference is small. Therefore, the current value which is actually limited is increased. Usually, when the
difference between the VIN pin and VOUT pin is small, on duty is decreased and the limited current value is
increased.
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