HA16107P Datasheet, PDF (6/40 Pages) Hitachi Semiconductor – PWM Switching Regulator for High-performance Voltage Mode Control

HA16107P/FP, HA16108P/FP
1. Timing in Normal Operation
Timing in these ICs is based on a triangular voltage waveform. The rising edge (leading edge) defines the deadband
time t_DB. The falling edge (trailing edge) defines the ON-duty control band t_ON. PWM output is on in the area
within t_ON that is bounded above by the triangle wave V_CT and error output V_E/O.
The following pin outputs are related to PWM control:
 C_T (pin 7): triangle-wave voltage output
 E/O (pin 15): error output voltage
 R_T2 (pin 8): ON-duty pulse output voltage
 OUT (pin 2): PWM pulse output (for driving the gate of a power MOS FET)
2. Triangle Oscillator, Waveform and Frequency
The triangle oscillator in these ICs generates a triangular waveform by charging and discharging timing capacitor C_T
with a constant current, as shown in the equivalent circuit. The C_T charge current is:
I(C_Tchg) = I₁ =
V_REF − 2V_BE
R_T1
The discharge current is:
I(C_Tdischg) = 2I₂ − I₁,
where
I₂ =
V_REF − 2V_BE
R_T2
In these equations Vref (reference voltage) is typically 6.45 V, and V_BE (base-emitter voltage of internal transistors)
is about 0.7 V.
The deadband time is:
t_DB
=
C_T × R_T1 × 2V
V_REF − 2V_BE
+ 0.25 µs
≈ 0.4 × C_T × R_T1 + 0.25 µs
The ON-duty time is:
t_ON
=
t_DB
×
R_T2
2R_T1 − R_T2
The 0.25 µs in these equations is a correction term for internal circuit delays.
The maximum ON-duty is
Du max =
R_T2
2R_T1
The oscillating frequency is:
f_OSC =
1
0.4 C_T R_T1 + 0.25 µ
1–
R_T2
2R_T1
+ 0.25 µ
1
=
(Hz)
0.8 C_T R_T12 + 0.25µ × 2R_T1
2R_T1 − R_T2
+ 0.25 µ
When R_T1 = R_T2, the maximum ON-duty is 50%, and:
1
f_OSC ≈ _{0.8 CT RT1 + 0.25 µ × 2 + 0.25 µ}
1
= _{0.8 CT RT1 + 0.75 µ} (Hz)
This approximation is fairly close, but it should be checked in-circuit.
Rev.4.00 Jun 15, 2005 page 6 of 39