The UC1842/3/4/5 family of control devices provides the necessary features to implement off-line or dc-to-dc fixed frequency current mode control schemes with a minimal external parts count

UC2845

Manufacturer Part NumberUC2845
DescriptionThe UC1842/3/4/5 family of control devices provides the necessary features to implement off-line or dc-to-dc fixed frequency current mode control schemes with a minimal external parts count
ManufacturerTexas Instruments
UC2845 datasheet
 


Specifications of UC2845

TopologyBoost, Flyback, ForwardControl MethodCurrent
Duty Cycle(max)(%)50Frequency(max)(khz)450
Uvlo Thresholds On/off(v)8.4/7.6Pin/package14SOIC, 8PDIP, 8SOIC
Vin(min)(v)7.6Vin(max)(v)30
Regulated Outputs(#)1Operating Temperature Range(c)-40 to 85
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CURRENT MODE PWM CONTROLLER
FEATURES
Optimized For Off-line and DC-to-DC
Converters
Low Start-Up Current (<1 mA)
Automatic Feed Forward Compensation
Pulse-by-Pulse Current Limiting
Enhanced Load Response Characteristics
Under-Voltage Lockout With Hysteresis
Double Pulse Suppression
High Current Totem Pole Output
Internally Trimmed Bandgap Reference
500-kHz Operation
Low R
Error Amp
O
V
7 12
cc
34 V
5
9
GROUND
4
7
OSC
R
/C
T
T
Error
Amp
V
2
3
FB
COMP
1
1
CURRENT
3
5
SENSE
Note 1:
A = DIL−8 Pin Number. B = SO−14 and CFP−14 Pin Number.
A/B
Note 2:
Toggle flip flop used only in 1844 and 1845.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
DESCRIPTION
The UC1842/3/4/5 family of control devices provides
the necessary features to implement off-line or
dc-to-dc fixed frequency current mode control
schemes with a minimal external parts count.
Internally implemented circuits include under-voltage
lockout featuring start up current less than 1 mA, a
precision reference trimmed for accuracy at the error
amp input, logic to insure latched operation, a PWM
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 UC1842 and UC1844 have UVLO
thresholds of 16 V
off-line applications. The corresponding thresholds
for the UC1843 and UC1845 are 8.4 V and 7.6 V.
The UC1842 and UC1843 can operate to duty cycles
approaching 100%. A range of zero to 50% is
obtained by the UC1844 and UC1845 by the addition
of an internal toggle flip flop which blanks the output
off every other clock cycle.
BLOCK DIAGRAM
UVLO
5 V
S/R
REF
2.50 V
VREF
Good
Logic
2R
R
1 V
CURRENT
SENSE
COMPARATOR
UC1842/3/4/5
UC2842/3/4/5
UC3842/3/4/5
SLUS223C – APRIL 1997 – REVISED JUNE 2007
and 10 V
, ideally suited to
ON
OFF
8 14
V
REF
5 V
50 mA
Internal
BIAS
7
11
V
C
6
10
T
OUTPUT
S
R
5
8
PWM
LATCH
POWER
GROUND
Copyright © 1997–2007, Texas Instruments Incorporated

UC2845 Summary of contents

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    ... COMPARATOR UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 SLUS223C – APRIL 1997 – REVISED JUNE 2007 and ideally suited to ON OFF REF Internal BIAS OUTPUT PWM LATCH POWER GROUND Copyright © 1997–2007, Texas Instruments Incorporated ...

  • Page 2

    UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 SLUS223C – APRIL 1997 – REVISED JUNE 2007 ABSOLUTE MAXIMUM RATINGS Low impedance source Supply voltage I CC Output current Output energy (capacitive load) Analog inputs (Pins 2, 3) Error amp output sink current T A Power ...

  • Page 3

    THERMAL CHARACTERISTICS over operating free-air temperature range (unless otherwise noted) PACKAGE DIL-8 SOIC-8 SOIC-14 CFP-14 PLCC-20 (1) data values stated were derived from MIL-STD-1835B. JC (2) Specified (junction to ambient) is for devices mounted range ...

  • Page 4

    UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 SLUS223C – APRIL 1997 – REVISED JUNE 2007 ELECTRICAL CHARACTERISTICS (continued) Unless otherwise stated, these specifications apply for –55 C UC284X for the 384X PARAMETER ERROR AMP SECTION Input Voltage ...

  • Page 5

    ERROR AMP CONFIGURATION Error amp can source or sink up to 0.5 mA UNDER-VOLTAGE LOCKOUT During under-voltage lock-out, the output drive is biased to sink minor amounts of current. Pin 6 should be shunted to ground with ...

  • Page 6

    UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 SLUS223C – APRIL 1997 – REVISED JUNE 2007 OSCILLATOR SECTION V 8 REF GROUND 5 1.72 For R > ...

  • Page 7

    OPEN-LOOP LABORATORY FIXTURE High peak currents associated with capacitive loads necessitate careful grounding techniques. Timing and bypas capacitors should be conected close to pin single point ground. The transistor and 5k potentiometer are used to sample ...

  • Page 8

    UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5 SLUS223C – APRIL 1997 – REVISED JUNE 2007 OFFLINE FLYBACK REGULATOR VARO 117 VAC 250 F 250 4 150 ...

  • Page 9

    PACKAGING INFORMATION Orderable Device (1) Package Type Package Status 5962-8670401PA ACTIVE CDIP 5962-8670401XA ACTIVE LCCC 5962-8670402PA ACTIVE CDIP 5962-8670402XA ACTIVE LCCC 5962-8670403PA ACTIVE CDIP 5962-8670403XA ACTIVE LCCC 5962-8670404DA ACTIVE CFP 5962-8670404PA ACTIVE CDIP 5962-8670404XA ACTIVE LCCC UC1842J ACTIVE CDIP ...

  • Page 10

    Orderable Device (1) Package Type Package Status UC2842D8 ACTIVE SOIC UC2842D8G4 ACTIVE SOIC UC2842D8TR ACTIVE SOIC UC2842D8TRG4 ACTIVE SOIC UC2842DG4 ACTIVE SOIC UC2842DTR ACTIVE SOIC UC2842DTRG4 ACTIVE SOIC UC2842J OBSOLETE CDIP UC2842N ACTIVE PDIP UC2842NG4 ACTIVE PDIP UC2843D ACTIVE ...

  • Page 11

    ... UC2844N ACTIVE PDIP UC2844NG4 ACTIVE PDIP UC2845D ACTIVE SOIC UC2845D8 ACTIVE SOIC UC2845D8G4 ACTIVE SOIC UC2845D8TR ACTIVE SOIC UC2845D8TRG4 ACTIVE SOIC UC2845DG4 ACTIVE SOIC Pins Package Qty (2) Eco Plan Drawing Ball Finish Green (RoHS CU NIPDAU for Pkg Type & no Sb/Br) ...

  • Page 12

    ... Orderable Device (1) Package Type Package Status UC2845DTR ACTIVE SOIC UC2845DTRG4 ACTIVE SOIC UC2845J OBSOLETE CDIP UC2845N ACTIVE PDIP UC2845NG4 ACTIVE PDIP UC3842D ACTIVE SOIC UC3842D8 ACTIVE SOIC UC3842D8G4 ACTIVE SOIC UC3842D8TR ACTIVE SOIC UC3842D8TRG4 ACTIVE SOIC UC3842DG4 ACTIVE SOIC ...

  • Page 13

    Orderable Device (1) Package Type Package Status UC3843D8TR ACTIVE SOIC UC3843D8TRG4 ACTIVE SOIC UC3843DG4 ACTIVE SOIC UC3843DTR ACTIVE SOIC UC3843DTRG4 ACTIVE SOIC UC3843N ACTIVE PDIP UC3843NG4 ACTIVE PDIP UC3843QTR OBSOLETE PLCC UC3844D ACTIVE SOIC UC3844D8 ACTIVE SOIC UC3844D8G4 ACTIVE ...

  • Page 14

    Orderable Device (1) Package Type Package Status UC3845D ACTIVE SOIC UC3845D8 ACTIVE SOIC UC3845D8G4 ACTIVE SOIC UC3845D8TR ACTIVE SOIC UC3845D8TRG4 ACTIVE SOIC UC3845DG4 ACTIVE SOIC UC3845DTR ACTIVE SOIC UC3845DTRG4 ACTIVE SOIC UC3845N ACTIVE PDIP UC3845NG4 ACTIVE PDIP (1) The ...

  • Page 15

    MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date ...

  • Page 16

    ... Device Package Package Type Drawing UC2842D8TR SOIC D UC2842DTR SOIC D UC2843D8TR SOIC D UC2843DTR SOIC D UC2844D8TR SOIC D UC2844DTR SOIC D UC2845D8TR SOIC D UC2845DTR SOIC D UC3842D8TR SOIC D UC3842DTR SOIC D UC3843D8TR SOIC D UC3843DTR SOIC D UC3844D8TR SOIC D UC3844DTR SOIC D UC3845D8TR SOIC D UC3845DTR SOIC D ...

  • Page 17

    ... Device Package Type UC2842D8TR SOIC UC2842DTR SOIC UC2843D8TR SOIC UC2843DTR SOIC UC2844D8TR SOIC UC2844DTR SOIC UC2845D8TR SOIC UC2845DTR SOIC UC3842D8TR SOIC UC3842DTR SOIC UC3843D8TR SOIC UC3843DTR SOIC UC3844D8TR SOIC UC3844DTR SOIC UC3845D8TR SOIC UC3845DTR SOIC ...

  • Page 18

    JG (R-GDIP-T8) 0.400 (10,16) 0.355 (9,00 0.065 (1,65) 0.045 (1,14) 0.063 (1,60) 0.015 (0,38) 0.023 (0,58) 0.015 (0,38) 0.100 (2,54) NOTES: A. All linear dimensions are in inches (millimeters). B. This drawing is subject to change without notice. ...

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    FN (S-PQCC-J**) 20 PIN SHOWN NO. OF PINS ** MIN 0.385 (9,78) 20 0.485 (12,32) 28 0.685 (17,40) 44 0.785 (19,94) 52 0.985 (25,02) 68 1.185 (30,10) 84 ...

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    ... Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements, and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are sold subject to TI’ ...