Fixed Frequency Current Mode PWM Controller
DESCRIPTION
FEATURES
APPLICATION
ORDERING INFORMATION
Temperature Range
Package Orderable Device Package Qty SOP8L
Pb-Free
UC3842D 75Units/Tube DIP8L PIN CONFIGURATION
UC3842P
50Units/Tube
UC3842 is a fixed frequency current-mode PWM controller. It is specially designed for Off Line and DC-to-DC converter applications with minimal external component. This
integrated circuit features a trimmed oscillator for precise duty cycle control, a temperature compensated reference, a high gain error amplifier, a current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET.
The device is protective features consisting of input and reference under-voltage lockouts each with hysteresis, cycle-by-cycle current limiting.
1234
5
678(Top View)
Compensation Voltage Feedback
Current Sense
R T /C T
V ref V CC Output GND
● Wireless Base Station Power ● Telecom and Datacom Power ● Industrial Power Systems ● PC Power Supplies
● Automatic Feed Forward Compensation ● High Current Totem Pole Output
● Internally Trimmed Bandgap Reference ● Undervoltage Lockout with Hysteresis ● Low Start Up Current
● Optimized for offline converter ● Double pulse suppression
● Current mode operation to 500kHz
0°C to +70°C
SCHEMATIC DIAGRAM
PIN DESCRIPTION
No.Name Function Description 1Compensation
This pin is the Error Amplifier output and is made available for loop compensation.
2
Voltage Feedback
This is the inverting input of the Error Amplifier. It is normally
connected to the switching power supply output through a resistor divider.
3
Current Sense A voltage proportional to inductor current is connected to this input
The PWM uses this information to terminate the output switch
conduction.4
R T /C T
The Oscillator frequency and maximum Output duty cycle are
programmed by connecting resistor RT to V REF and capacitor C T to ground. Operation to 500kHz is possible.
5GND This pin is the combined control circuitry and power ground. 6
Output
This output directly drives the gate of a power MOSFET.Peakcurrents up to 1.0A are sourced and sunk by this pin.7V CC This pin is the positive supply of the control IC.
8
V REF
This is the reference output. It provides charging current for capacitor C T through resistor R T
Figure 1. Simplified Block Diagram
V R T Voltage Input
Output
C Current Sense Input
Pin numbers in parenthesis are for the D suffix SOIC-14 package.
ABSOLUTE MAXIMUM RATINGS
Symbol
Value
Unit Total Power Supply and Zener Current I CC + I Z
30
DC Supply Voltage
V CC 30V Output Current I o ±1.0A Output Energy (Capacitive Load per Cycle) W 5.0µJ Error Amp Output Sink Current
I oe 10mA Current Sense and Voltage Feedback Inputs V IN -0.3 to 5.5 V Maximum Power Dissipation @T A =25°C P D 0.862W Thermal Resistance, Junction-to-Air R BIA 145°C/W Maximum Operating Junction Temperature T J +150 °C Storage Temperature Range
T STG
-65 to +150
Parameter
Symbol
Min
Max
Unit
DC Supply Voltage V CC
1225V
mA
°C
Parameter
Operating Temperature
T A
70
°C
ELECTRICAL CHARACTERISTICS
(Vcc = 15V unless otherwise noted)
Parameter
Symbol
Test Conditions
Min
Max
Unit
4.9
5.1
Reference Out V REF
4.865
5.135
V
Line Regulation Reg LINE 20
mV Load Regulation
Reg LOAD
25
mV
Total Output Variation
over Line, Load,
Temperature (Note1) V FINAL 4.82 5.18V
Output Short Circuit Current
I SC -30-180 mA
RECOMMENDED OPERATION CONDITIONS
I O = 1.0mA, V CC = 15V,T A = 25±10°C
IO = 1.0mA, V CC = 15V, T A = T LOW to T HIGH V CC = 12V to 25V, T A = T LOW to T HIGH I O = 1.0 to 20mA, T A = T LOW to T HIGH V CC = 12V, I O = 1.0mA,T A = T LOW to T HIGH V CC = 25V, I O = 20mA, T A = T LOW to T HIGH
V CC =15V Reference Section
V CC = 15V, T J = 25°C R T =10K ¡, C T = 3.3nF 4757
Frequency f osc
V CC = 15V ,
T A = T LOW to T HIGH ,
R T = 10K ¡ C T = 3.3nF
46
60
kHz
Frequency Change with Voltage
Δ f osc /ΔV 1.0%
T J = 25°C 7.59.3
Discharge Current
I disch V osc = 2.0V V CC = 15V
T A = T LOW to T HIGH
7.2
9.5
mA
Error Amplifier Section Voltage Feedback Input
V FB V O = 2.5V ,V CC = 15V,T A = T LOW to T HIGH
2.42 2.58
V Input Bias Current I IB V FB = 2.7V,V CC = 15V,TA = T LOW to T HIGH
-2.0
μA Open Loop Voltage Gain
A VOL
V O = 2.0V to 4.0V,V CC = 15V,
T A = T LOW to T HIGH 65
dB
Unity Gain Bandwidth
BW V CC = 15V,
T A = T LOW to T HIGH 0.7MHz Power Supply Rejection Ratio
PSRR
V CC = 12V to 25V,T A = T LOW to T HIGH
60dB
Sink I SINK
V O = 1.1V, V FB = 2.7V,V CC = 15V,
T A = T LOW to T HIGH 2.0
Output Current
Source I SOURCE
V O = 5.0V, V FB = 2.3V,V CC = 15V,
T A = T LOW to T HIGH -0.5
mA
High State V OH 5.0
Output Voltage Swing
Low State
V OL
V FB = 2.7V, V CC = 15V R L(5.0) = 15KΩ,T A = T LOW to T HIGH
1.1
V
Oscillator Section
V FB = 2.7V, V CC = 15V R L(GND) = 15KΩ,T A = T LOW to T HIGH ELECTRICAL CHARACTERISTICS
Parameter Symbol
Test Conditions
Min
Max
Unit
V CC = 12V to 25V,
T A = T LOW to T HIGH,
R T =10kΩ, C T =3.3nF
Output Section I SINK = 20mA, V CC = 15V 0.4Low State V OL I SINK = 200mA, V CC = 15V 2.2
13Output Voltage
High State
V OH 12
V
Output Voltage with UVLO Activated V OL(UVLO)
V CC = 6V, I SINK = 1.0mA,T A = T LOW to T HIGH 1.1
V t r C L = 1.0nF,V CC = 15V,T A = T LOW to T HIGH 150
ns Output Voltage Fall Time
t f
150
ns
Under Voltage Lock out Section Startup Threshold
V th
7.87.9V Minimum Operating
Voltage After Turn-On V CC(MIN)
7.0
8.2
V
PWM Section Duty Cycle DC
V CC = 15V,
T A = T LOW to T HIGH ,
R T = 10KΩ, C T = 3.3nF
0 94%
Total Device
Startup: V CC = 14V 1.0Power Supply Current I CC Operating: V CC = 15V 17mA
Power Supply Zener Voltage
V z I CC = 25mA, V CC = 0 to 40V
30
40
V
Note 1: V FINAL = V REF25(Reg LINE +Reg LOAD )/1000±IV REF70(V REF0)-V REF25I V REF25
= V REF @T A =25°C;V REF70=V REF @T A =70°C;V REF0=V REF @T A =0°C.Note 2: T LOW = 0°C,T HIGH =+70°C
I SINK = 20mA, V CC = 15V I SINK = 200mA, V CC = 15V V CC = 0V to 25V, T A = T LOW to T HIGH Output Voltage Rise Time
Current Sense Section
Current Sense Input Voltage Gain
A V V F
B = 0V, V C
C = 15V,T A = T LOW to T HIGH 2.85 3.15 Maximum Current Sense Input Threshold V TH 0.9
1.1V Input Bias Current I IB
-10
μA
Propagation Delay (Current Sense Input to Output) t PLH 300ns
V FB = 0V,V CC = 15V,T A = T LOW to T HIGH V CC = 15V,
T A = T LOW to T HIGH V CC = 15V,
T A = T LOW to T HIGH
ELECTRICAL CHARACTERISTICS(CONTINUE)
Parameter
Symbol
Test Conditions
Min
Max
Unit
C L = 1.0nF, V CC = 15V,T A = T LOW to T HIGH V CC = 0V to 25V, T A = T LOW to T HIGH
Figure 2. Timing Resistor versus Oscillator Frequency Figure 3. Output Deadtime versus Oscillator Frequency
Figure 4. Oscillator Discharge Current versus Temperature Figure 5. Maximum Output Duty Cycle versus Timing Resistor
Figure 6. Error Amp Small Signal
Transient Response Figure 7. Error Amp Large Signal
Transient Response
2.55V
2.5V 2.45V
2.5V
3.0V
2.0V
50
20105.02.01.0
TYPICAL PERFORMANCE CHARACTERISTICS
f OSC ,OSCILLATOR FREQUENCY (Hz)
R T , T I M I N G R E S I S T O R (k Ω)
% D T ,P E R C E N T O U T P U T D E A D R M E
f OSC ,OSCILLATOR FREQUENCY (Hz)
I d i s c h g , D I S C H A R G E C U R R E N T (m A )
-55
-25
0255075100125
T A , AMBIENT TEMPERATURE (°C)
D m a x , M A X I M U M O U T P U T D U T Y C Y C L
E (%)
RT, TIMING RESISTOR (Ω)
V CC = 15 V A V = -1.0T A = 25°C
20 m V /D I V
0.5 μs/DIV
V CC = 15 V A V = -1.0T A = 25°C
20 m V /D I V
0.1 μs/DIV
