S-9365AAAAAI6TIG2 SII [Seiko Instruments Inc], S-9365AAAAAI6TIG2 Datasheet - Page 22

• Manufacturer Part Number: S-9365AAAAAI6TIG2
• Description: STEP-UP, SUPER-SMALL PACKAGE, 1.2 MHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
• Manufacturer: SII [Seiko Instruments Inc]

22
S-8365/8366 Series
STEP-UP, SUPER-SMALL PACKAGE, 1.2 MHz PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
5. External transistor
5.1 Bipolar NPN type
5.2 Enhanced MOS FET type
A bipolar (NPN) or enhanced (Nch) MOS FET transistor can be used as an external transistor.
The driving ability to increase output current by using a bipolar transistor is determined based on the h
and R
Smaller R
pulses or the V
experimentation.
Inserting a speed-up capacitor (C
and increases efficiency.
Select a speed-up capacitor for which the C
Actually, however, the optimum C
so determine the optimum value based on experimentation.
Use an Nch power MOS FET. A MOS FET that has low ON-resistance (R
ideal for gaining efficiency. The ON-resistance and input capacitance generally have a tradeoff relationship.
ON-resistance is efficient in the range where the output current is high with relatively low frequency switching,
and input capacitance is efficient in the range where the output current is medium to low with high frequency
switching. Therefore, select a MOS FET for which the ON-resistance and input capacitance are optimum under
your usage conditions.
The input voltage (V
withstand voltage is higher than the maximum value used for the input voltage, and for which the drain
withstand voltage is greater than or equal to the output voltage (V
If a MOS FET for which the threshold value is near the UVLO detection voltage is used, a high current flows
upon power-on, and, in the worst case, the output voltage might not increase and the timer latch type
short-circuit protection circuit might operate. Therefore, select a MOS FET for which the threshold value is
sufficiently lower than the UVLO detection voltage.
The recommended R
the bipolar transistor by using I
R
b
=
b
V
value of the bipolar transistor. Figure 19 shows the peripheral circuit.
DD
b
I
− 0.7
b
values increase the output current, but decrease the efficiency. Actually, the current might flow on
DD
－
or V
DD
I
EXTH
0.4
b
SS
) is supplied as the gate voltage of a MOS FET, so select a MOS FET for which the gate
value is around 1 kΩ. Calculate the required base current (I
voltage might drop due to wiring resistance, so determine the optimum value based on
b
Figure 19 External Transistor Peripheral Circuit
=
b
b
) in parallel with the R
value varies depending on the characteristics of the bipolar transistor used,
h
I
PK
FE
Pch
Nch
Seiko Instruments Inc.
, and then select an R
b
V
value satisfies C
DD
EXT
b
resistor as shown in Figure 19 reduces switching loss
2200 pF
1 kΩ
b
C
R
≤
b
b
b
value smaller than that determined using:
OUT
2 × π × R
) + the forward voltage of the diode (V
b
I
PK
1
× f
ON
OSC
) and input capacitance (C
× 0.7
b
) based on the h
.
Rev.1.1
FE
FE
value of
ISS
D
value
).
_00
) is