MB3782 Datasheet, PDF (10/28 Pages) Fujitsu Component Limited. – Switching Regulator Controller

MB3782
s USING THE RT PIN
The triangular waves, as shown in Figure 1, act to set the oscillator frequency by charging and discharging the
capacitor connected to the CT pin using the current value of the resistor connected to the RT pin.
In addition, when voltage level VREF/2 is output to external circuits from the RT pin, care must be taken in making
the external circuit connections to adjust for the fact that I1 is increased by the value of the current I2 to the
external circuits in determining the oscillator frequency (see Figure 2).
Triangular wave oscillator
VREF
2
2
IRT
RT
1
ICT
CT
ICT = IRT
= ^VREF
2RT
Figure 1 No VREF/2 connection to external circuits from RT pin
Triangular wave generator
To external circuits
VREF
2
2
IRT
IRT
I1
RT
1
ICT
CT
ICT = IRT
= I1 + I2
=
VREF
2RT
+ I2
Figure 2 VREF/2 connection to external circuits from RT pin
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