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 I
O
, determined by an external timing resistor R
T
, is
made to flow continuously to external timing capacitor C
T
. When the C
T
pin voltage exceeds the
comparator threshold voltage V
H
, the comparator output causes a switch to operate, discharging a current I
O
from C
T
. Next, when the C
T
pin voltage drops below threshold voltage V
L
, the comparator output again
causes the switch to operate, stopping the I
O
discharge. The triangle wave is generated by this repeated
operation.
Note that I
O
= 1.1 V/R
T
. Since the I
O
current mirror circuit has a very limited current producing ability, R
T
should be set to
≥
5 kΩ (I
O
≥
220
µA).
With this IC series, V
H
and V
L
of the triangle wave are fixed internally at about 1.6 V and 1.0 V by the
internal resistors R
A
, R
B
, and R
C
. The oscillator frequency can be calculated as follows.
f
OSC
=
Here,
t
1
=
t
2
=
C R
⋅
(V
H
−
V
L
)
C
T
⋅
(V
H
−
V
L
)
=
T T
1.1 V/R
T
1.1 V
C R
⋅
(V
H
−
V
L
)
C
T
⋅
(V
H
−
V
L
)
=
T T
= t
1
(2
−
1)
×
1.1 V/R
T
1.1 V
1
t
1
+ t
2
+ t
3
V
H
−
V
L
= 0.6 V
t
1
= t
2
=
0.6
C R
1.1
T T
t
3
≈
0.8
µs
(comparator delay time in the oscillator)
Accordingly,
f
OSC
≈
1
1
[Hz]
≈
2t
1
+ t
3
1.1 C
T
R
T
+ 0.8
µs
Note that the value of f
OSC
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.
Rev.2.0, Sep.18.2003, page 8 of 33
RENESAS [ RENESAS TECHNOLOGY CORP ]
