NCP1252ADR2G ON Semiconductor, NCP1252ADR2G Datasheet - Page 16

• Manufacturer Part Number: NCP1252ADR2G
• Description: IC PWM CTLR CURRENT MODE 8-SOIC
• Manufacturer: ON Semiconductor

Specifications of NCP1252ADR2G

• Frequency - Max: 500kHz
• Pwm Type: Current Mode
• Number Of Outputs: 1
• Duty Cycle: 50%
• Voltage - Supply: 9 V ~ 28 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: -25°C ~ 125°C
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Duty Cycle (max): 48 %
• Mounting Style: SMD/SMT
• Switching Frequency: 92 KHz to 550 KHz
• Maximum Operating Temperature: + 125 C
• Fall Time: 22 ns
• Rise Time: 26 ns
• Synchronous Pin: No
• Topology: Flyback, Forward
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

added to prevent sub−harmonics oscillation.
ramp compensation.
•
•
•
•
•
•
any sub−harmonics oscillation in case of duty cycle above 50%.
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Table 4. ORDERING INFORMATION
Specification Brochure, BRD8011/D.
NCP1252ADR2G
NCP1252BDR2G
NCP1252CDR2G
Internal ramp compensation level
Secondary−side downslope projected over the sense resistor is:
Natural primary ramp:
Thus the natural ramp compensation is:
Here the natural ramp compensation is lower than the desired ramp compensation, so an external compensation should be
We can know calculate external resistor (R
Thus with R
The following example illustrates a power supply where the natural ramp offers enough ramp compensation to avoid external
2 switch−Forward Power supply specification:
Secondary−side downslope projected over the sense resistor is:
The natural primary ramp is:
And the natural ramp compensation will be:
So in that case the natural ramp compensation due to the magnetizing inductance of the transformer will be enough to prevent
Regulated output: 12 V
L
V
Current sense resistor: 0.75 W
Switching frequency: 125 kHz
V
power supply works.
out
f
bulk
= 0.7 V (drop voltage on the regulated output)
= 27 mH
= 350 V, minimum input voltage at which the
comp
Device
S
S
= 510 W, 100% compensation ramp is applied on the CS pin.
sense
sense
Ratio +
+
+
R
S
(V
comp
(V
natural
S
S
out
out
sense
natural
L
L
S
d
d
out
+ R
out
) V
) V
natural_comp
int
natural_comp
+
(d
+
+
V
L
ramp
f
comp
f
)
)
mag
DC
bulk
N
N
V
N
N
V
L
ramp
s
p
p
mag
s
bulk
S
1 * Ratio
max
R
* d
R
R
int
Ratio
sense
comp
sense
sense
+
+
R
F
natural_comp
sense
sw
S
S
S
S
) to reach the correct compensation level.
natural
å S
sense
natural
A version
B version
C version
å S
å S
sense
Version
å S
http://onsemi.com
å R
å S
sense
natural
sense
int
å d
å d
natural
comp
)
+ 3.5
å Ratio +
+
natural_comp
+
natural_comp
16
0.84
+
+ 26.5 @ 10
(12 ) 0.7)
(12 ) 0.7)
+
27 @ 10
13 @ 10
27 @ 10
•
•
•
•
•
125 kHz + 520 mV
7 @ 10
350
Duty cycle max: DC
V
R
Targeted ramp compensation level: 100%
Transformer specification:
350
ramp
ramp
29.99 @ (1.00 * 0.67)
−6
−3
+ 20.19
−6
+ 37.5
− L
− N
−3
= 3.5 V, Internal ramp level.
= 26.5 kW, Internal pull−up resistance
0.085
0.75 + 20.19 mV
0.085
29.99
0.75 + 37.5 mV
29.99
3
mag
s
1 * 0.019
/N
Marking
1252A
1252B
1252C
0.019
p
520
= 7 mH
+ 67.3%
= 0.085
+ 125%
0.75 + 29.99 mV
0.75 + 29.99 mV
+ 509 W
ms
max
= 84%
+ 0.019
ms
ms
2500/Tape & Reel
2500/Tape & Reel
2500/Tape & Reel
ms
ms
Shipping
†