UC2844BNG View Datasheet(PDF) - ON Semiconductor
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UC2844BNG Datasheet PDF : 19 Pages
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UC3844B, UC3845B, UC2844B, UC2845B
VCC
Vin
7(12)
8(14)
4(7)
R2
2(3)
1(1)
R1
VClamp ≈
R
Bias
5.0V Ref
+
-
R
Osc
+
1.0 mA
+
-
VClamp
EA
2R
R
1.0V
T
S
Q
R
Comp/Latch
7(11)
Q1
6(10)
5(8)
3(5)
RS
5(9)
1.67
ǒ Ǔ R2
ǒ Ǔ R1
)
1
+ 0.33x10-3
R1R2
R1 ) R2
Where: 0 ≤ VClamp ≤ 1.0 V
Ipk(max)
[
VClamp
RS
Figure 20. Adjustable Reduction of Clamp Level
8(14)
R
Bias
5.0V Ref
R
+
-
Osc
4(7)
+
T
1.0mA
S
2(3)
Q
2R
R
1.0M
EA
R
1.0V
1(1)
C
5(9)
tSoft-Start ≈ 3600C in mF
Figure 21. Soft−Start Circuit
VCC
Vin
7(12)
8(14)
R
Bias
5.0V Ref
+
-
R
+
-
Osc
4(7)
+
VClamp
1.0 mA
2(3)
EA
R2
1(1)
R1 MPSA63
2R
R
1.0V
5(9)
T
S
Q
R
Comp/Latch
7(11)
Q1
6(10)
5(8)
3(5)
RS
1.67
ǒ Ǔ VClamp ≈
R2
R1
)
1
Where: 0 ≤ VClamp ≤ 1.0 V
ƪ ƫ tSoftStart + * In
1
*
VC
3VClamp
C
R1 R2
R1 ) R2
Ipk(max)
[
VClamp
RS
VCC
Vin
(12)
VPin 5
[
RS Ipk rDS(on)
rDM(on) ) RS
5.0V Ref
+
-
+
-
T
S
Q
R
If: SENSEFET = MTP10N10M
RS = 200
Then : VPin 5 [ 0.075 Ipk
(11)
G
(10)
D SENSEFET
S
K
M
(8)
Comp/Latch
(5)
RS
1/4 W
Power Ground:
To Input Source
Return
Control Circuitry Ground:
To Pin (9)
Virtually lossless current sensing can be achieved with the implementation
of a SENSEFETt power switch. For proper operation during over-current
conditions, a reduction of the Ipk(max) clamp level must be implemented.
Refer to Figures 20 and 22.
Figure 22. Adjustable Buffered Reduction of
Clamp Level with Soft−Start
Figure 23. Current Sensing Power MOSFET
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