cs52845 ON Semiconductor, cs52845 Datasheet - Page 5

• Manufacturer Part Number: cs52845
• Description: Current Mode Pwm Control Circuit
• Manufacturer: ON Semiconductor

Figure 2: Timing Diagram
Figure 3: Duty Cycle parameters.
F/F Output
EA Output
RESET
Current
Toggle
Switch
V
OSC
V
OSC
V
CC
I
O
O
V
V
upper
lower
t
t
on
off
=t
=t
t
t
on
c
c
c
+2t
d
t
d
t
off
Circuit Description:: continued
5
The times T
High peak currents associated with capacitive loads neces-
sitate careful grounding techniques. Timing and bypass
capacitors should be connected close to Gnd in a single
point ground.
The transistor and 5k potentiometer are used to sample
the oscillator waveform and apply an adjustable ramp to
Sense.
Substituting in typical values for the parameters in the
above formulas:
then
For better accuracy R
t
t
V
t
t
c
d
c
d
REF
= R
= R
= R
c
0.5534R
and T
= 5.0V, V
T
T
T
C
C
C
T
T
T
ln
Setting the Oscillator
ln
d
ln
T
can be determined as follows:
(
(
C
(
T
upper
V
V
2.3 - 0.0083 R
4.0 - 0.0083 R
V
T
V
Grounding
should be 10k .
REF
REF
REF
REF
= 2.7V, V
- I
- I
- V
- V
d
d
R
R
upper
lower
T
T
- V
- V
T
T
lower
)
upper
lower
)
= 1.0V, I
)
d
= 8.3mA,