FUJITSU MB39A104 - Manual (Page 13)

MB39A104
13
■ SETTING THE OUTPUT VOLTAGE
■ SETTING THE TRIANGULAR OSCILLATION FREQUENCY
The triangular oscillation frequency is determined by the timing capacitor (C
T
) connected to the CT terminal (pin
13), and the timing resistor (R
T
) connected to the RT terminal (pin 12).
Moreover, it shifts more greatly than the calculated values according to the constant of timing resistor (R
T
) when
the triangular wave oscillation frequency exceeds 1 MHz. Therefore, set it referring to “Triangular Wave Oscillation
Frequency vs. Timing Resistor” and “Triangular Wave Oscillation Frequency vs. Timing Capacitor” in “
■ TYPICAL
CHARACTERISTICS”.
Triangular oscillation frequency : f
OSC
−
+
+
15
10
14 (CS2)
CS1
( −INE2)
−INE1
V O
R1
R2
1.24 V
Error Amp
1.24
R2
V O (V) =
(R1 + R2)
11
• Output Voltage Setting Circuit
f
OSC
(kHz) :=
1200000
C
T
(pF) × R
T
(k Ω)