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PDF UC3842B Fiche technique - American First Semiconductor

Numéro de référence UC3842B
Description UC3842B/3B/4B/5B - High Performance Current Mode Controllers
Fabricant American First Semiconductor 
Logo American First Semiconductor Logo 

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UC3842B Datasheet, Description
High Performance Current Mode Controllers
General Description
UC3842B/3B/4B/5B,UC2842B/3B
Package outline
The UC3842B/3B/4B/5B, series are high performance fixed
frequency current mode controllers. They are specifically designed for
Off–Line and dc–to–dc converter applications offering the designer a
cost–effective solution with minimal external components. These
integrated circuits feature a trimmed oscillator for precise duty cycle
control, a temperature compensated reference, high gain error
amplifier, current sensing comparator, and a high current totem pole
output ideally suited for driving a power MOSFET.
Also included are protective features consisting of input and
reference undervoltage lockouts each with hysteresis, cycle–by–cycle
current limiting, programmable output deadtime, and a latch for single
pulse metering.
These devices are available in an 8–pin dual–in–line and surface
mount (SO–8) plastic package as well as the 14–pin plastic surface
mount (SO–14). The SO–14 package has separate power and ground
pins for the totem pole output stage.
The UCX842B has UVLO thresholds of 16 V (on) and 10 V (off),
ideally suited for off–line converters. The UCX843B is tailored for
lower voltage applications having UVLO thresholds of 8.5 V (on) and
7.6 V (off).
Features
Trimmed Oscillator for Precise Frequency Control
Oscillator Frequency Guaranteed at 250 kHz
Current Mode Operation to 500 kHz
Automatic Feed Forward Compensation
Latching PWM for Cycle–By–Cycle Current Limiting
Internally Trimmed Reference with Undervoltage Lockout
High Current Totem Pole Output
Undervoltage Lockout with Hysteresis
Low Startup and Operating Current
Vref
8(14)
RT/CT
4(7)
Voltage
Feedback
Input
2(3)
Output
Compensation
1(1)
VCC 7(12)
R
5.0V
Reference
VCC
Undervoltage
Lockout
R
Vref
Undervoltage
Lockout
Oscillator
+
-
Error
Amplifier
Latching
PWM
Gnd 5(9)
Pin numbers in parenthesis are for the D suffix SO-14 package.
Figure 1. Simplified Block Diagram
VC
7(11)
Output
6(10)
Power
Ground
5(8)
Current
Sense
3(5) Input
8
1
8
1
DIP-8
SOP-8
14
1
SOP-14
Pin Connections
Compensation 1
Voltage Feedback 2
Current Sense 3
RT/CT 4
8 Vref
7 VCC
6 Output
5 Gnd
(Top View)
Compensation 1
NC 2
Voltage Feedback 3
NC 4
Current Sense 5
NC 6
RT/CT 7
14 Vref
13 NC
12 VCC
11 VC
10 Output
9 Gnd
8 Power Ground
(Top View)
@ 2010 Copyright By American First Semiconductor
Page 1/16
UC3842B Fiche technique
UC3842B/3B/4B/5B,UC2842B/3B
Electrical Characteristics(VCC = 15 V [Note 4], RT = 10 k, CT = 3.3 nF. For typical values TA = 25°C, for min/max values
TA is the operating ambient temperature range that applies [Note 5], unless otherwise noted.)
UC284XB
UC384XB
Characteristics
Symbol Min Typ Max Min Typ Max
Error Amplifier Section
Voltage Feedback Input (VO = 2.5 V)
Input Bias Current (VFB = 5.0 V)
Open Loop Voltage Gain (VO = 2.0 V to 4.0 V)
Unity Gain Bandwidth (TJ = 25°C)
Power Supply Rejection Ratio (VCC = 12 V to 25 V)
Output Current
Sink (VO = 1.1 V, VFB = 2.7 V)
Source (VO = 5.0 V, VFB = 2.3 V)
Output Voltage Swing
High State (RL = 15 k to ground, VFB = 2.3 V)
Low State (RL = 15 k to Vref, VFB = 2.7 V)
(UC284XB, UC384XB)
VFB
IIB
AVOL
BW
PSRR
2.45 2.5 2.55 2.42 2.5 2.58
– – 0.1 –1.0 – – 0.1 – 2.0
65 90 – 65 90 –
0.7 1.0 – 0.7 1.0 –
60 70 – 60 70 –
ISink 2.0 12 – 2.0 12 –
ISource
– 0.5 –1.0
– 0.5 –1.0
VOH 5.0 6.2 – 5.0 6.2 –
VOL
– 0.8 1.1 – 0.8 1.1
Current Sense Section
Current Sense Input Voltage Gain (Notes 6 & 7)
(UC284XB, UC384XB)
Maximum Current Sense Input Threshold (Note 6)
(UC284XB, UC384XB)
Power Supply Rejection Ratio (VCC = 12 V to 25 V, Note 6)
Input Bias Current
Propagation Delay (Current Sense Input to Output)
Output Section
Output Voltage
Low State (ISink = 20 mA)
(ISink = 200 mA) (UC284XB, UC384XB)
High State (ISource = 20 mA) (UC284XB, UC384XB)
(ISource = 200 mA)
Output Voltage with UVLO Activated (VCC = 6.0 V, ISink = 1.0 mA)
Output Voltage Rise Time (CL = 1.0 nF, TJ = 25°C)
Output Voltage Fall Time (CL = 1.0 nF, TJ = 25°C)
Undervoltage Lockout Section
Startup Threshold (VCC)
UCX842B/4B
UCX843B/5B
AV
Vth
PSRR
IIB
tPLH(In/Out)
VOL
VOH
VOL(UVLO)
tr
tf
Vth
2.85
0.9
13
12
15
7.8
3.0
1.0
70
– 2.0
150
0.08
1.4
13.5
13.0
0.1
45
35
16
8.4
3.15
1.1
–10
300
0.4
2.2
1.1
150
150
17
9.0
2.85
0.9
13
12
14.5
7.8
3.0
1.0
70
– 2.0
150
0.08
1.4
13.5
13.0
0.1
45
35
16
8.4
3.15
1.1
–10
300
0.4
2.2
1.1
150
150
17.5
9.0
Minimum Operating Voltage After Turn–On (VCC)
UCX842B/4B
UCX843B/5B
VCC(min)
9.0 10 11 8.5 10
7.0 7.6 8.2 7.0 7.6
4. Adjust VCC above the Startup threshold before setting to 15 V.
5. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible.
Tlow = 0°C for UC3842B/3B/4B/5B; –25°C for UC2842B/3B
Thigh = +70°C for UC3842B/3B/4B/5B; +85°C for UC2842B/3B
6. This parameter is measured at the latch trip point with VFB = 0 V.
7. Comparator gain is defined as: AV
V Output Compensation
V Current Sense Input
11.5
8.2
Unit
V
µA
dB
MHz
dB
mA
V
V/V
V
dB
µA
ns
V
V
ns
ns
V
V
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Page 3/16

3 Page

UC3842B pdf
UC3842B/3B/4B/5B,UC2842B/3B
VCC = 15 V
IO = 1.0 mA to 20 mA
TA = 25°C
VCC = 12 V to 25
TA = 25°C
2.0 ms/DIV
Figure 12. Reference Load Regulation
0
ÄÄÄ ÄÄÄÄÄÄÄÄÄVCC
Source Saturation
VCC = 15 V
(Load to Ground) 80 µs Pulsed Load
ÄÄÄÄÄÄÄÄÄÄÄÄÄ-1.0 TA=25°C
120 Hz Rate
ÄÄÄÄÄ-Ă2.0
ÄÄÄÄTA = -Ă55°C
3.0
ÄÄÄTA = -Ă55°C
ÄÄÄ ÄÄÄ2.0
TA = 25°C
ÄÄÄÄ ÄÄ1.0 Sink Saturation
(Load to VCC)
Gnd
ÄÄÄÄ ÄÄ0
0 200 400 600 800
IO, OUTPUT LOAD CURRENT (mA)
Figure 14. Output Saturation Voltage
versus Load Current
VCC = 30 V
CL = 15 pF
TA = 25°C
100 ns/DIV
Figure 16. Output Cross Conduction
2.0 ms/DIV
Figure 13. Reference Line Regulation
90%
VCC = 15 V
CL = 1.0 nF
TA = 25°C
10%
50 ns/DIV
Figure 15. Output Waveform
25
20
15
10
RT = 10 k
ÄÄÄÄCT = 3.3 nF
5 VFB = 0 V
ÄÄÄÄISense = 0 V
ÄÄÄÄTA = 25°C
0
0 10 20 30 40
VCC, SUPPLY VOLTAGE (V)
Figure 17. Supply Current versus Supply Voltage
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