参数资料
型号: UC3844NG
厂商: ON Semiconductor
文件页数: 10/16页
文件大小: 0K
描述: IC REG CTRLR PWM CM 8-DIP
产品变化通告: Product Discontinuation 15/May/2006
标准包装: 50
PWM 型: 电流模式
输出数: 1
频率 - 最大: 60kHz
占空比: 50%
电源电压: 10 V ~ 30 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: 0°C ~ 70°C
封装/外壳: 8-DIP(0.300",7.62mm)
包装: 管件
其它名称: UC3844NGOS
UC3844, UC3845, UC2844, UC2845
7(12)
V CC
V in
8(14)
R
5.0V ref
+
?
+
R
Bias
+
+
?
?
7(11)
5.0V ref
4(7)
+
OSC
?
V Clamp
T
6(10)
Q1
8(14)
R
R
Bias
+
+
?
R2
2(3)
+
?
EA
1.0mA
2R
R
?
+
S
Q
R
Comp/Latch
5(8)
4(7)
+
OSC
?
T
R1
1(1)
5(9)
1.0V
3(5)
R S
2(3)
+
?
EA
1.0mA
2R
R
?
+
S
R
Q
I pk(max) ≈
V Clamp
1.67
R 2
+1
R 1
+ 0.33 x 10 ?3
R 1 R 2
R 1 + R 2
V Clamp
R S
Where: 0 ≤ V Clamp ≤ 1.0 V
C
1(1)
t Soft?Start   3600C in m F
5(9)
1.0V
Figure 20. Adjustable Reduction of Clamp Level
Figure 21. Soft ? Start Circuit
7(12)
V CC
V in
C
I pk(max) ≈
5.0V ref
R
+
+
?
+
2R
R
R 1 R 2
+
+
R S I pk r DS(on)
V Pin 5 ≈
S
(10) G K
R S
R2
R1
8(14)
4(7)
2(3)
1(1)
MPSA63
V Clamp
V Clamp
R S
+
?
+
?
R
Bias +
?
?
OSC
T
V Clamp
1.0mA S
Q
R
EA
Comp/Latch
1.0V
5(9)
1.67
+ 0.33 x 10 ?3
R 2 R 1 + R 2
+1
R 1
Where: 0 ≤ V Clamp ≤ 1.0 V
+
?
7(11)
6(10)
5(8)
3(5)
Q1
R S
?
5.0V ref
+
?
?
+
(12)
+
?
?
T
S
Q
R
Comp/Latch
Control CIrcuitry
Ground:
To Pin (9)
V CC
(11)
(8)
(5) Return
V in
r DM(on) + R S
If: SENSEFET = MTP10N10M
R S = 200
Then: V pin 5 = 0.075 I pk
D SENSEFET
M
Power Ground
To Input Source
1/4 W
t Softstart = ? In
1?
V C
3V Clamp
C
R 1 R 2
R 1 + R 2
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
I pk(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
7(12)
V CC
V in
5.0V ref
+
?
+
+
+
?
?
7(11)
?
T
6(10)
Q1
?
+
S
R
Q
5(8)
Comp/Latch
R
3(5)
C
R S
The addition of the RC filter will eliminate
instability caused by the leading edge spike on
the current waveform.
Figure 24. Current Waveform Spike Suppression
http://onsemi.com
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