Application Note: AN_SY50282
Buck Regulator
with CC/CV control
Preliminary Specification
General Description
Features
The SY50282 is a PWM controller with several features
to enhance performance of Buck converters. It integrates
a MOSFET with 500V breakdown voltage to decrease
physical volume. Both current and voltage regulation are
achieved by the controller. It drives the Buck converter
in the quasi-resonant mode to achieve higher efficiency
and better EMI performance.
Ordering Information
• Fast Startup (
VBUS
264V × 1.414
=
=186kΩ
I VIN_OVP
2mA
Sil
R ST <
Set RST
AN_SY50282 Rev.0.2
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11
AN_SY50282
R ST =4.7M
(b) Design CVIN
VBUS
-IST ) × t ST ( 90V × 1.414 -15µA) × 1.5s
R ST
4.7MΩ
CVIN =
=
=1.3µF
VVIN_ON
14V
(
Set CVIN
CVIN =1µF
#8 Set current sense resistor to achieve ideal output current
0.25A
tia
l-P
re
p
IOUT,LIM
ar
ed
Known conditions at this step
VREF
0.675V
The current sense resistor is
VREF
RISET =
= 1.04
2 I OUT ⋅ 1.3
VCOMP _ MAX
0.9
RISET _MIN =
=
= 0.88
I PK
1.02
fo
r
Refer to constant-current control
fid
en
Because the saturation current of Mosfet is 1.4A, the current limit is set in 1.02A to consider the margin, so the sense
resistance is not less than 0.88Ohm.(The circuit has a good start-up performance in 250mA output when sense resistor
is set in 0.88Ohm. )
.C
on
#7. Set ZCS pin
Refer to VOUT
Co
rp
First identify RZCSU need for line regulation.
Parameters Designed
RZCSU
200kΩ
er
gy
Then compute RZCSD
Sil
Conditions
VOUT
12V
RZCSU
200kΩ
R ZCSU
200K
R ZCSD =
=
= 22.1K
VOUT
12V
− 1)
-1 (
1.25V
VZCS,REF
VZCS_REF
1.25V
R ZCSD =22kΩ
#10 final result
AN_SY50282 Rev.0.2
Silergy Corp. Confidential- Prepared for Customer Use Only
12
Sil
er
gy
Co
rp
.C
on
fid
en
tia
l-P
re
p
ar
ed
fo
r
AN_SY50282
AN_SY50282 Rev.0.2
Silergy Corp. Confidential- Prepared for Customer Use Only
13
AN_SY50282
4.80 - 5.00
.C
on
1.40 - 1.60
0.25 base
0.18 - 0.25
en
°
-8
fid
0
45°
0.25 - 0.50
tia
l-P
re
p
0.60
Recommended Pad Layout
1.27 (TYP)
Co
rp
0.60 - 0.85
0.30 – 0.50
0.08 - 0.25
ar
ed
fo
r
5.40
3.80 - 4.00
1.27 TYP
5.80 - 6.20
6.10
1.55
SO8 Package Outline & PCB Layout Design
Sil
er
gy
Notes: All dimensions are in millimeters.
All dimensions don’t include mold flash & metal burr.
AN_SY50282 Rev.0.2
Silergy Corp. Confidential- Prepared for Customer Use Only
14
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