HA16114P Datasheet, PDF (7/38 Pages) Hitachi Semiconductor – Switching Regulator for Chopper Type DC/DC Converter

HA16114P/PJ/FP/FPJ, HA16120FP/FPJ
The oscillator frequency f_OSC can be calculated as follows.
f_OSC =
1
t₁ + t₂ + t₃
Here, t₁ =
t2 =
C_T × (V_H − V_L)
1.1 V/R_T
C_T × (V_H − V_L)
3 × 1.1 V/R_T
t3 ≈ 0.8 µs (comparator delay time)
Since V_H − V_L = 0.6 V
f_OSC ≈
1
0.73 × C_T × R_T + 0.8 (µs)
(Hz)
At high frequencies the comparator delay causes the sawtooth wave to overshoot the 1.6 V threshold and
undershoot the 1.0 V threshold, and changes the dead-band thresholds accordingly. Select constants by
testing under implementation conditions.
Current
mirror
1.1 V
3.2 V
(Internal voltage)
1:4
C_T charging
I_O
Oscillator
comparator
Discharg
-ing 3I_O
R_T
C_T
I_O
External circuit
V_H = 1.6 V typ
Vref
2.5 V
R_A
R_C
R_B
Sync
circuit
SYNC
V_L = 1.0 V typ
t₂
t₁ : t₂ = 3 : 1
t₁
Figure 1.1 Equivalent Circuit of Oscillator
7