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UC2843B Datasheet

(UC2842B - UC2845B) HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

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UC2842B/3B/4B/5B
® UC3842B/3B/4B/5B
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
. TRIMMED OSCILLATOR FOR PRECISE FRE-
QUENCY CONTROL
. OSCILLATOR FREQUENCY GUARANTEED
AT 250kHz
. CURRENT MODE OPERATION TO 500kHz
. AUTOMATIC FEED FORWARD COMPENSA-
TION
. LATCHING PWM FOR CYCLE-BY-CYCLE
CURRENT LIMITING
. INTERNALLY TRIMMED REFERENCE WITH
UNDERVOLTAGE LOCKOUT
. HIGH CURRENT TOTEM POLE OUTPUT
. UNDERVOLTAGE LOCKOUT WITH HYSTER-
ESIS
. LOW START-UP AND OPERATING CURRENT
Minidip
SO8
comparatorwhich alsoprovidescurrent limit control,
and a totem pole output stage designed to source
or sink high peakcurrent. The outputstage, suitable
for driving N-Channel MOSFETs, is low in the off-
state.
DESCRIPTION
Differences between members of this family are the
under-voltagelockout thresholds and maximum duty
TheUC384xB family ofcontrolICs providesthe nec- cycle ranges. The UC3842B and UC3844B have
essary features to implement off-line or DC to DC UVLO thresholds of 16V (on) and 10V (off), ideally
fixed frequency current mode control schemes wwwwit.DhataSheet4Us.cuomitedoff-lineapplicationsThecorrespondingthresh-
a minimal external parts count. Internally imple- oldsforthe UC3843BandUC3845Bare8.5 V and7.9
mented circuits include a trimmed oscillator for pre- V. The UC3842B and UC3843B can operate to duty
cise DUTY CYCLE CONTROL under voltage lock- cycles approaching 100%. A range of the zero to <
outfeaturingstart-up current less than0.5mA,a pre- 50 % is obtained by the UC3844B and UC3845B by
cision reference trimmed for accuracy at the error the addition of an internal toggle flip flopwhich blanks
amp input, logicto insure latched operation,a PWM the output off every otherclock cycle.
BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B)
7
Vi
5
GROUND
4
RT/CT
VFB
COMP
CURRENT
SENSE
2
1
3
34V UVLO
S/R
5V
REF
2.50V
OSC
VREF GOOD
LOGIC
INTERNAL
BIAS
T
8 VREF
5V 50mA
6
OUTPUT
ERROR AMP.
+
-
2R
R
S
R
1V
CURRENT
SENSE
COMPARATOR
PWM
LATCH
UC3842B
D95IN331
March 1999
1/15


STMicroelectronics Electronic Components Datasheet

UC2843B Datasheet

(UC2842B - UC2845B) HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

No Preview Available !

UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
ABSOLUTE MAXIMUM RATINGS
Sy mb o l
P ar ame te r
Vi Supply Voltage (low impedance source)
Vi Supply Voltage (Ii < 30mA)
IO Output Current
EO Output Energy (capacitive load)
Analog Inputs (pins 2, 3)
Error Amplifier Output Sink Current
Ptot Power Dissipation at Tamb 25 °C (Minidip)
Ptot Power Dissipation at Tamb 25 °C (SO8)
Tstg Storage Temperature Range
TJ Junction Operating Temperature
TL Lead Temperature (soldering 10s)
* All voltages are with respect to pin 5, all currents are positive into the specified terminal.
PIN CONNECTION (top view)
M ini dip/ SO 8
Valu e
30
Self Limiting
±1
5
– 0.3 to 5.5
10
1.25
800
– 65 to 150
– 40 to 150
300
Un it
V
A
µJ
V
mA
W
mW
°C
°C
°C
COMP
VFB
ISENSE
RT/CT
18
27
36
45
D95IN332
VREF
Vi
OUTPUT
GROUND
PIN FUNCTIONS
No Function
Description
1 COMP This pin is the Error Amplifier output and is made available for loop compensation.
2 VFB This is the inverting input of the Error Amplifier. It is normally connected to the switching
power supply output through a resistor divider.
3 ISENSE A voltage proportional to inductor current is connected to this input. The PWM uses this
information to terminate the output switch conduction.
4 RT/CT The oscillator frequency and maximum Output duty cycle are programmed by connecting
resistor RT to Vref and cpacitor CT to ground. Operation to 500kHz is possible.
5 GROUND This pin is the combined control circuitry and power ground.
6 OUTPUT This output directly drives the gate of a power MOSFET. Peak currents up to 1A are sourced
and sunk by this pin.
7 VCC This pin is the positive supply of the control IC.
8 Vref This is the reference output. It provides charging current for capacitor CT through resistor RT.
ORDERING NUMBERS
SO8
UC2842BD1; UC3842BD1
UC2843BD1; UC3843BD1
UC2844BD1; UC3844BD1
UC2845BD1; UC3845BD1
Minidip
UC2842BN; UC3842BN
UC2843BN; UC3843BN
UC2844BN; UC3844BN
UC2845BN; UC3845BN
2/15


Part Number UC2843B
Description (UC2842B - UC2845B) HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
Maker ST Microelectronics
Total Page 15 Pages
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