UC3845A

Pinout




Specifications

Symbol	Parameter	Value	Unit
Vi	SupplyVoltage(lowimpedance source)	30	V
Vi	SupplyVoltage(Ii < 30mA)	SelfLimiting
IO	OutputCurrent	±1	A
EO	OutputEnergy (capacitive load)	5	J
	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

Description

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.