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UC3844BN Datasheet

HIGH-PERFORMANCE 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
DESCRIPTION
The UC384xB family of control ICs 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 current less than 0.5mA, a pre-
cision reference trimmed for accuracy at the error
amp input, logic to insure latched operation, a PWM
Minidip
SO8
comparator which also provides current limit control,
and a totem pole output stage designed to source
or sink high peak current. The output stage, suitable
for driving N-Channel MOSFETs, is low in the off-
state.
Differences between members of this family are the
under-voltage lockout thresholds and maximum duty
cycle ranges. The UC3842B and UC3844B have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding thresh-
olds for the UC3843B and UC3845B are 8.5 V and 7.9
V. The UC3842B and UC3843B can operate to duty
cycles approaching 100%. A range of the zero to <
50 % is obtained by the UC3844B and UC3845B by
the addition of an internal toggle flip flop which blanks
the output off every other clock cycle.
BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B)
7
Vi
5
GROUND
4
RT/CT
2
VFB
1
COMP
CURRENT 3
SENSE
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

UC3844BN Datasheet

HIGH-PERFORMANCE PWM CONTROLLER

No Preview Available !

UC2842B/3B/4B/5B - UC3842B/3B/4B/5B
ABSOLUTE MAXIMUM RATINGS
Symbol
Parameter
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)
Minidip/SO8
Value
30
Self Limiting
±1
5
– 0.3 to 5.5
10
1.25
800
– 65 to 150
– 40 to 150
300
Unit
V
A
µJ
V
mA
W
mW
°C
°C
°C
COMP
VFB
ISENSE
RT/CT
1
8
2
7
3
6
4
5
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 UC3844BN
Description HIGH-PERFORMANCE PWM CONTROLLER
Maker ST Microelectronics
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UC3844BN Datasheet PDF






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