S-8340A25AFT-T2-X Datasheet, PDF (18/55 Pages) Seiko Instruments Inc – SWITCHABLE SWITCHING REGULATOR CONTROLLER

STEP-UP, 600 kHz, PWM CONTROL OR PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8340/8341 Series
Rev.4.0_01
The soft-start circuit of the S-8340/8341 Series increases the duty ratio gradually as shown in Figure 10.
The soft-start time (tSS) can be set with an external capacitor (CSS).
Figure 10 Image of EXT Pin Waveform
If fOSC = 600 kHz and CSS = 4700 pF, the time until the duty ratio of 50% is reached is 9.7 ms (typ.).
If VIN ≥ 2 V, the approximate time until a specific duty ratio is reached is calculated from the following formula :
8.336 × Duty [%] + 682.45
If fOSC = 600 kHz, tSS [ms] = CSS [pF] ×
535000
If fOSC = 300 kHz, tSS [ms] = CSS [pF] × ^{6.564 × Duty [%] + 698}
229000
Even if the IC reaches a certain duty at a duty ratio of 0 to 43%, there may be a delay of the output voltage (VOUT) in
reaching the specified voltage (VOUT(S)). This delay occurs due to the delay of the error amplifier reference voltage
in reaching the specified voltage (1.0 V). Note that the maximum delay time may be the value calculated when a
duty ratio is 43%.
3. ON/OFF Pin (Shutdown Pin)
The ON/OFF pin stops or starts the step-up operation.
When the ON/OFF pin is set to "L", all the internal circuits stop operating, reducing power consumption. The EXT
pin voltage becomes equal to the VSS voltage, thereby turning off the switching transistor.
The ON/OFF pin is configured as shown in Figure 11 and is not either pulled up or pulled down. So, do not use it
in a floating state. Applying 0.3 to 0.8 V to the ON/OFF pin increases current consumption. So do not apply such
voltage. When the ON/OFF pin is not used, connect it to the VDD pin. The ON/OFF pin does not have hysterisis.
VDD
ON/OFF
VSS
Figure 11 ON/OFF Pin Structure
ON/OFF Pin CR Oscillation Circuit
Output Voltage
“H”
Operating
Set value
“L”
Stopped
≅VIN^*1
*1. Voltage obtained by extracting the voltage drop due to DC
resistance of the inductor and the diode forward voltage from VIN.
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