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HA16116FP Datasheet, PDF (8/34 Pages) Hitachi Semiconductor – Switching Regulator for Chopper Type DC/DC Converter
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HA16116FP/FPJ, HA16121FP/FPJ
The triangle wave is a voltage waveform used as a reference in creating a PWM pulse. This block operates
according to the following principles. A constant current IO, determined by an external timing resistor RT,
is made to flow continuously to external timing capacitor CT. When the CT pin voltage exceeds the
comparator threshold voltage VH, the comparator output causes a switch to operate, discharging a current IO
from CT. Next, when the CT pin voltage drops below threshold voltage VL, the comparator output again
causes the switch to operate, stopping the IO discharge. The triangle wave is generated by this repeated
operation.
Note that IO = 1.1 V/RT. Since the IO current mirror circuit has a very limited current producing ability, RT
should be set to ≥ 5 kΩ (IO ≥ 220 µA).
With this IC series, VH and VL of the triangle wave are fixed internally at about 1.6 V and 1.0 V by the
internal resistors RA, RB, and RC. The oscillator frequency can be calculated as follows.
fOSC
=
1
t1 + t2 + t3
Here,
t1 =
CT ⋅ (VH − VL)
1.1 V/RT
= CT RT ⋅ (VH − VL)
1.1 V
t2 =
CT ⋅ (VH − VL)
(2 − 1) × 1.1 V/RT
=
CT RT ⋅ (VH − VL)
1.1 V
=
t1
VH − VL = 0.6 V
t1 = t2 =
0.6
1.1
CT RT
t3 ≈ 0.8 µs (comparator delay time in the oscillator)
Accordingly,
fOSC ≈
1
2t1 + t3
≈
1
1.1 CT RT + 0.8 µs
[Hz]
Note that the value of fOSC may differ slightly from the above calculation depending on the amount of delay
in the comparator circuit. Also, at high frequencies this comparator delay can cause triangle wave
overshoot or undershoot, skewing the dead band threshold. Confirm the actual value in implementation
and adjust the constants accordingly.
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