UC2844N Просмотр технического описания (PDF) - Motorola => Freescale
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UC2844N Datasheet PDF : 14 Pages
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UC3844, 45 UC2844, 45
Figure 19. Adjustable Reduction of Clamp Level
VCC
7(12)
Vin
8(14)
4(7)
R2
2(3)
1(1)
R1
R
Bias
R
Osc
+
+–
EA
1.0mA
2R
R
5.0Vref
+
–+
+
–
+–
–
VClamp
–+
1.0V
T
S
Q
R
Comp/Latch
5(9)
7(11)
Q1
6(10)
5(8)
3(5)
RS
VClamp
1.67
R2 + 1
R1
+ 0.33 x 10–3
R1 R2
R1 + R2
Ipk(max) ≈
VClamp
RS
Where: 0 ≤ VClamp ≤ 1.0 V
Figure 20. Soft–Start Circuit
8(14)
R
Bias
R
5.0Vref
+
+–
Osc
4(7)
+
–
T
+
1.0mA
–
2(3)
EA
2R
R
S
–+
RQ
1.0V
C
1(1)
tSoft–Start 3600C in µF
5(9)
Figure 21. Adjustable Buffered Reduction of
Clamp Level with Soft–Start
VCC
7(12)
Vin
8(14)
R
Bias
R
5.0Vref
+
+–
+– +
–
4(7)
2(3)
R2
1(1)
Osc
+
+–
EA
1.0mA
2R
R
–
VClamp
–+
1.0V
T
S
RQ
Comp/Latch
C
MPSA63
5(9)
R1
VClamp
1.67
+ 0.33 x 10–3 R1 R2
R2 + 1
R1 + R2
R1
Ipk(max)≈
VClamp
RS
Where: 0 ≤ VClamp ≤ 1.0 V
tSoftstart = – In
1–
VC
3VClamp
C
R1 R2
R1 + R2
7(11)
Q1
6(10)
5(8)
3(5)
RS
Figure 22. Current Sensing Power MOSFET
5.0Vref
+ +–
–
VCC
(12)
+– +
–
(11)
Vin
VPin
5
≈
RS Ipk rDS(on)
rDM(on) + RS
If: SENSEFET = MTP10N10M
RS = 200
Then: Vpin 5 = 0.075 Ipk
D SENSEFET
S
T
S
–+ R Q
Comp/Latch
Control CIrcuitry
Ground:
To Pin (9)
(10) G M
(8)
(5) RS
1/4 W
K
Power Ground
To Input Source
Return
Virtually lossless current sensing can be achieved with the implement of a SENSEFET
power switch. For proper operation during over current conditions, a reduction of the
Ipk(max) clamp level must be implemented. Refer to Figures 19 and 21.
Figure 23. Current Waveform Spike Suppression
VCC
7(12)
Vin
5.0Vref
+
–+
+ +–
–
–
T
S
–
+
Q
R
Comp/Latch
7(11)
Q1
6(10)
5(8)
R
3(5)
C
RS
The addition of the RC filter will eliminate
instability caused by the leading edge spike on
the current waveform.
10
MOTOROLA ANALOG IC DEVICE DATA
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