HA17524P Datasheet, PDF (4/18 Pages) Hitachi Semiconductor – Switching Regulator Controller

HA17524P/FP
Blocks Description
Oscillator: The oscillation frequency f is calculated from the following equations. Figure 3 shows one
example.
f 1.15/(R_T •C_T)
R_T = 1.8k to 100 k Ω
C_T = 0.001µ to 0.1 µF
f = 140 Hz to 500 kHz
1M
400 k
100 k
40 k
10 k
4k
1k
400
V_CC = 20 V
Ta = 25°C
C
T _{= 0.001 µF}
C
T _{= 0.01 µF}
C
T _{= 0.1 µF}
100
1k
4 k 10 k 40 k 100 k
Timing Resistance R_T ( Ω)
Figure 3 Oscillating Frequency vs Timing Resistance
Then the ramp wave shown in figure 4 is available at pin 7, C_T terminal, since C_T is charged by the constant
current I generated by R_T.
4