UC3842A
High Performance Current Mode Controller

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The UC384xA family of controlICs provides the nec- essary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count. Internally imple-mented circuits include a trimmed oscillator for pre-cise DUTY CYCLE CONTROL under voltage lock- out featuring start-up currentl ess than0.5mA,a pre-cision reference trimmed for accuracyat the error am pinput,logicto insure latched operation,a PWM comparatorwhich also providescurrent limit control, and a totem pole output stage designed to source or sink high peak current.The outputstage,suitable for driving N-Channel MOSFETs, is low in the off-state.

Differences between member softh is family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC3842A and UC3844A have UVLO thresholds of 16V (on) and 10V (off), ideally suitedoff lineapplications The corresponding thresh- olds for the UC3843A and UC3845A are 8.5V and 7.9V.The UC3842A and UC3843A can operate to dutycycles approa ching100%.A range of the zero to <50 is obtained by the UC3844A and UC3845A by the addition of an internal toggle flip flop which blanks the out put off every otherclock cycle.
Symbol
Parameter
Value
Unit
Vi
SupplyVoltage(lowimpedance source)
30
V
Vi
SupplyVoltage(Ii < 30mA)
SelfLimiting
IO
OutputCurrent
±1
A
EO
OutputEnergy (capacitive load)
5
μJ
AnalogInputs (pins2, 3)
–0.3to 5.5
V
ErrorAmplifierOutput SinkCurrent
10
mA
Ptot
PowerDissipation at Tamb ≤ 25°C (Minidip)
1.25
W
Ptot
PowerDissipation at Tamb≤ 25°C (SO8)
800
mW
Tstg
Storage Temperature Range
–65to 150
°C
TJ
Junction OperatingTemperature
–40to 150
°C
TL
LeadTemperature (soldering 10s)
300
°C

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Datasheet

Size: 262.89KB
Page: 6
PDF: UC3842A.pdf
  • Description:
    High Performance Current Mode Controller
  • MFG:
    FCI [First Components International]
 

Abstract


UC3842A High Performance
Current Mode Controller
l Trimmed Oscillator Discharge Current for Precise Duty
Cycle Control
l Current Mode Operation to 500 kHz
l Automatic Feed Forward Compensation
l Latching PWM for Cycle–By–Cycle Current Limiting
l Internally Trimmed Reference with Undervoltage Lockout
l High Current Totem Pole Output
l Undervoltage Lockout with Hysteresis
l Low Startup and Operating Current
CS SUFFIX
PLASTIC PACKAGE
SOP-14
The UC3842A series of high performance
fixed frequency current mode controllers are
specifically designed for off–line and dc–to–dc
converter applications offering the designer a cost
effective solution with minimal external components.
This integrated circuit features 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.
This device is available in an 8–pin dual–in–
line 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 UC3842A has UVLO thresholds of
16V(on) and 10V(off), ideally suited for off–line
converters.
CD SUFFIX
PLASTIC PACKAGE
8 DIP
PIN CONNECTIONSSIMPLIFIED BLOCK DIAGRAM
Pin numbers adjacent to terminals are for the D suffix 8-DIP package.
Pin numbers in parenthesis are for the S suffix SOP–14 package.
NOTES: 1. Maximum Package power dissipation limits must be observed.
2. Adjust VCC above the Startup threshold before setting to 15 V.
3. Low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible
Tlow = 0 C, Thigh = +70 C.
4. This parameter is measured at the latch trip point with V
FB
= 0V.
5. Comparator gain is defined as: A
V
D V Output Compensation
D V Current Sense Input
D8 SUFFIX
PLASTIC PACKAGE
8 SOP

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