UC2845BN datasheet, PDF - EEWORLD Datasheet

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UC2845BN: DescriptionCurrent Mode PWM Controller 1A 500kHz 8-Pin PDIP Tube; CategoryPower/power management The power supply circuit; File Size163KB，15 Pages; ManufacturerSTMicroelectronics; Websitehttp://www.st.com/; Environmental Compliance

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UC2845BN Overview

Current Mode PWM Controller 1A 500kHz 8-Pin PDIP Tube

UC2845BN Parametric

Parameter Name	Attribute value
EU restricts the use of certain hazardous substances	Compliant
ECCN (US)	EAR99
Part Status	Active
HTS	8542.39.00.01
Type	Current Mode PWM Controller
Control Method	Current Mode PWM Controller
Topology	Boost\|Flyback
Number of PWM Outputs	1
Switching Frequency (kHz)	500
Maximum Duty Cycle (%)	50
Rise Time (ns)	50
Output Current (mA)	1000(Max)
Fall Time (ns)	50
Maximum Operating Supply Voltage (V)	30
Maximum Supply Current (mA)	17
Maximum Power Dissipation (mW)	1250
Adjustable Output	No
On/Off Pin	No
Synchronous Pin	No
Minimum Operating Temperature (°C)	-25
Maximum Operating Temperature (°C)	85
Packaging	Tube
Supplier Package	PDIP
Pin Count	8
Standard Package Name	DIP
Mounting	Through Hole
Package Height	3.32
Package Length	10.92(Max)
Package Width	6.6(Max)
PCB changed	8
Lead Shape	Through Hole

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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

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

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)

34V

GROUND

UVLO

S/R

REF

INTERNAL

BIAS

VREF GOOD

LOGIC

RT/CT

OSC

ERROR AMP.

VREF

5V 50mA

2.50V

OUTPUT

VFB

COMP

CURRENT

SENSE

CURRENT

SENSE

COMPARATOR

PWM

LATCH

UC3842B

D95IN331

March 1999

1/15

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