HA16654A Datasheet, PDF (12/15 Pages) Hitachi Semiconductor – PWM Controlled Switching Regulator

HA16654A, HA16664A Series
500 k
OSC Frequency vs. Timing Resistor (HA16654A)
200 k
CT =220 pF
CT = 560 pF
OSC Frequency vs. Timing Resistor (HA16664A)
200 k
150 k
C_T = 220 pF
C_T = 560 pF
100 k
10 k
20 k
50 k 100 k
Timing Resistor R_T (kΩ)
200 k
100 k
10 k
20 k
50 k 100 k
Timing Resistor R_T (Ω)
200 k
Formula for the oscillation frequency f
f = 1 / [ {C_T (R_T + 1 × 10³)(a ⋅ R_T + b) / (Vref − V_BE)} + 100 × 10^−9]
C_T : Timing capacitor (F)
R_T : Timing resistor (Ω)
Vref : Reference voltage 5.0 (V) (Typ)
V_BE : Base-emitter voltage 0.65 (V) (Typ)
The following table show empirical values of
a and b for different values of C_T.
C_T (pF)
220
560
a
−2.30 × 10^−6
−8.37 × 10^−6
b
1.247
1.575
Also,
f ≈ 4.35 / (C_T ⋅ R_T)
−2
−4
−6
−8
−10
200
1.2
a
1.3
1.4
b
1.5
1.6
300 400 500 600
C_T (pF)
12