UNISONIC TECHNOLOGIES UC3844, UC3845 DATA SHEET

UNISONIC TECHNOLOGIES CO., LTD

UC3844/45 LINEAR INTEGRATED CIRCUIT

HIGH PERFORMANCE
CURRENT MODE PWM
CONTROLLERS

 DESCRIPTION

The UTC UC3844/3845 are high performance fixed frequency

current mode controllers that specifically designed for Off-Line and
DC to DC converter applications with minimal external parts count.

The differences between UC3844 and UC3845 are the maximum

duty cycle ranges and under-voltage lockout thresholds. The

UC3844 ideally suited to off-line applications with UVLO thresholds

of 16V

8.5V

 FEATURES

(ON)

and 7.6V

(ON)

and 10V

(OFF)

, and UC3845 has UVLO thresholds of

(OFF)

for lower voltage applications.

*Pb-free plating product number:

UC3844L/UC3845L

* Operation output switching frequency up to 500 kHz
* Output deadtime adjustable from 50% to 70%
* Automatic feed forward compensation
* Latching PWM for cycle-by-cycle current limiting
* High current totem pole output
* Internally trimmed reference with under voltage lockout
* UVLO with hysteresis
* Low startup and operating current

 ORDERING INFORMATION

Order Number

Normal Lead Free Plating
UC3844-D08-T UC3844L-D08-T DIP-8 Tube
UC3844-S08-R UC3844L-S08-R SOP-8 Tape Reel
UC3844-S08-T UC3844L-S08-T SOP-8 Tube
UC3845-D08-T UC3845L-D08-T DIP-8 Tube
UC3845-S08-R UC3845L-S08-R SOP-8 Tape Reel
UC3845-S08-T UC3845L-S08-T SOP-8 Tube

Package Packing

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UC3844/45 LINEAR INTEGRATED CIRCUIT

 PIN CONFIGURATION

 PIN DESCRIPTION

PIN NO PIN NAME FUNCTION

1 Compensation Error amplifier output, this pin is made available for loop compensation.

2 VFB

3 ISENSE

4 RT/CT

5 GND Power ground.

6 Output

7 VCC Positive supply.
8 V

REF

Voltage Feedback, the inverting input of the Error Amplifier. It is normally connected to the
switching power supply output through a resistor divider.
A voltage proportional to inductor current is connected to this input. The PWM uses this
information to terminate the output switch conduction.
The Oscillator frequency and maximum output duty cycle are programmed by connecting
resistor R

This output directly drives the gate of a power MOSFET. Peak currents up to 1A are
sourced and sunk by this pin. The output switches at one-half the oscillator frequency.

Reference output, provides charging current for capacitor CT though resistor RT.

to Vref and capacitor CT to ground. Operation to 1 MHz is possible.

T

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UC3844/45 LINEAR INTEGRATED CIRCUIT

 BLOCK DIAGRAM

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