MB3778 Datasheet, PDF (17/29 Pages) Fujitsu Component Limited. – Switching Regulator Controller

MB3778
s USING THE RT TERMINAL
The triangular waves, as shown in Figure “No VREF/2 connection to external circuits from RT terminal”, act to set
the oscillator frequency by charging and discharging the capacitor connected to the CT terminal using the current
value of the resistor connected to the RT terminal.
In addition, when voltage level VREF/2 is output to external circuits from the RT terminal, 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 “VREF/2 connection to external circuits
from RT terminal”).
• No VREF/2 connection to external circuits from RT terminal
Triangular wave
oscillator
( ) VREF
2
2
IRT
RT
1
ICT
CT
ICT = IRT
=
VREF
2RT
• VREF/2 connection to external circuits from RT terminal
Triangular wave
oscillator
To external circuits
( ) VREF
2
2
IRT
I2
I1
RT
1
ICT
CT
ICT = IRT
= I1 + I2
=
VREF
2RT
+
I2
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