UC2845BD1 查看數據表（PDF） - Motorola => Freescale
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UC2845BD1 Datasheet PDF : 16 Pages
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UC3844B, 45B UC2844B, 45B
Figure 19. Adjustable Reduction of Clamp Level
VCC
Vin
7(12)
8(14)
R
Bias
5.0V Ref
+
–
4(7)
R2
2(3)
R
Osc
+
1.0 mA
+
–
VClamp
EA
2R
R
1.0V
T
S
Q
R
Comp/Latch
7(11)
Q1
6(10)
5(8)
1(1)
3(5)
RS
R1
5(9)
ǒ ) Ǔ ǒ ) Ǔ [ VClamp ≈
1.67
R2
R1
1
+ 0.33x10–3
R1R2
R1 R2
Where: 0 ≤ VClamp ≤ 1.0 V
Ipk(max)
VClamp
RS
Figure 20. Soft–Start Circuit
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 µF
Figure 21. Adjustable Buffered Reduction of
Clamp Level with Soft–Start
VCC
Vin
7(12)
8(14)
R
Bias
5.0V Ref
+
–
R
+
–
4(7)
2(3)
R2
Osc
+
1.0 mA
VClamp
EA
2R
R
1.0V
T
S
Q
R
Comp/Latch
1(1)
C
R1 MPSA63
5(9)
7(11)
Q1
6(10)
5(8)
3(5)
RS
1.67
VClamp ≈ R2
ǒ ) ǓR1
1
Where: 0 ≤ VClamp ≤ 1.0 V
+ * ƪ * ƫ ) [ tSoft-Start
In 1
VC
3VClamp
C
R1
R1
R2
R2
Ipk(max)
VClamp
RS
Figure 22. Current Sensing Power MOSFET
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 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.
10
MOTOROLA ANALOG IC DEVICE DATA
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