UC2845D ON Semiconductor, UC2845D Datasheet - Page 10
UC2845D
Manufacturer Part Number
UC2845D
Description
Other Power Management 52kHz 1A Current PWM
Manufacturer
ON Semiconductor
Type
High Performance Current Mode Controllersr
Datasheet
1.UC2845DR2.pdf
(16 pages)
Specifications of UC2845D
Output Voltage Range
4.95 V to 5.05 V
Input Voltage Range
30 V
Operating Temperature Range
- 25 C to + 85 C
Mounting Style
SMD/SMT
Package / Case
SOIC-14
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
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V
Clamp
I
C
pk(max)
R2
R1
t
Softstart
Figure 22. Adjustable Buffered Reduction of
8(14)
R2
R1
4(7)
2(3)
1(1)
≈
8(14)
Figure 20. Adjustable Reduction of Clamp Level
4(7)
R
R
2(3)
1(1)
= − In
MPSA63
1.67
2
1
V
V
Clamp
Clamp
R
+ 1
S
Clamp Level with Soft−Start
+
−
EA
R
R
+
−
+ 0.33 x 10
1 −
+
Where: 0 ≤ V
EA
R
R
R
R
OSC
1.67
2
1
1.0mA
Bias
+
3V
OSC
+ 1
1.0mA
Bias
V
2R
Clamp
−3
C
R
+ 0.33 x 10
2R
Clamp
R
5(9)
V
C
≤ 1.0 V
Clamp
R
5(9)
−
R
+
V
1.0V
1
5.0V
1
R
Clamp
−3
R
+ R
1
−
+
R
1
−
+
1.0V
5.0V
+
−
+ R
2
ref
2
R
−
+
−
+
R
2
5.0V
+
−
R
2
ref
1
1
Comp/Latch
+ R
−
+
Comp/Latch
S
R
+
−
R
ref
T
Q
2
S
R
2
Comp/Latch
T
Figure 24. Current Waveform Spike Suppression
Q
I
S
R
pk(max)
+
T
−
Q
Where: 0 ≤ V
+
−
+
7(12)
−
≈
+
−
+
7(12)
−
V
+
Clamp
7(12)
−
R
http://onsemi.com
Clamp
V
S
CC
7(11)
6(10)
5(8)
3(5)
V
CC
7(11)
6(10)
5(8)
3(5)
≤ 1.0 V
V
CC
7(11)
6(10)
5(8)
3(5)
10
Q1
Q1
R
V
R
V
S
in
S
in
C
R
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)
−
+
5.0V
Figure 23. Current Sensing Power MOSFET
Q1
R
V
clamp level must be implemented. Refer to Figures 20 and 22.
−
+
+
−
S
in
ref
C
Comp/Latch
S
R
The addition of the RC filter will eliminate
instability caused by the leading edge spike on
the current waveform.
T
Q
Control CIrcuitry
8(14)
4(7)
2(3)
1(1)
t
+
To Pin (9)
−
Soft−Start
Ground:
Figure 21. Soft−Start Circuit
+
(12)
−
3600C in mF
+
−
EA
R
R
V
CC
+
(11)
(10)
(8)
(5)
OSC
1.0mA
Bias
G
1/4 W
R
2R
M
S
D
R
SENSEFET
V
in
To Input Source
K
Power Ground
5(9)
S
If: SENSEFET = MTP10N10M
Return
V
−
Pin
+
1.0V
5.0V
Then: V
5 ≈
−
+
+
−
ref
R
r
pin
S
DM(on)
R
S
R
T
I
S
5 = 0.075 I
pk
Q
= 200
r
DS(on)
+ R
S
pk