3

UCC1839

UCC2839

UCC3839

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

Precision Reference

REF

4.95

5

5.05

V

4.9

5.1

V

VA+/REF

0.298

0.3

0.302

V/V

VDD Regulator

VDD

7

7.5

8

V

1.3

2

mA

Note 1: Guaranteed by design. Not 100% tested in production.

CA–: Current Error Amplifier Negative Input.

CAO: Current Error Amplifier Output. Output source cur-

rent is limited, and output sink current is guaranteed to

be greater than the VAO output source current. Current

loop compensation components are generally connected

to CAO and CA–.

CA+: Current Error Amplifier Positive Input.

CS–: Current Sense Amplifier Negative Input.

CSO: Current Sense Amplifier Output. Internally set gain

CS+: Current Sense Amplifier Positive Input.

GM: Gm (transconductance) Programming Pin. Resistor

Ω to GND.

GND: Chip Ground.

LED: Output of LED Driver. Connect LED from VDD pin

to LED.

REF: 5V Precision Reference Buffer Output. Minimum

Decoupling Capacitance = 0.01

µF

VA–: Voltage Error Amplifier Negative Input. Voltage Er-

ror Amplifier is internally referenced to 1.5V

VAO: Voltage Error Amplifier Output. In a two loop aver-

age current mode control configuration, VAO is con-

nected to CA+ and is the current command signal. VAO

is internally clamped not to exceed 5V for short circuit

control. In a single loop voltage mode control configura-

tion with a parallel average short circuit current control

loop, VAO is connected directly to CAO. Output source

current is limited, and output sink current is guaranteed

to be greater than the CAO output source current.

VDD: 7.5V Regulator output.

Supply for most of the

chip. Minimum Decoupling Capacitance = 0.01

µF

VGATE: External FET Gate Control Voltage.

PIN DESCRIPTIONS

Fig. 1 shows a typical secondary side average current

mode controller configuration using the UCC3839. In this

configuration, output voltage is sensed and regulated by

the voltage error amplifier. Its output, VAO provides the

reference for the current error amplifier at the CA+ pin.

VAO can be connected to CA+ directly or through a re-

sistive divider depending on the particular application re-

quirements.

Average current mode control needs accurate output cur-

rent information which is provided by a low value current

sense resistor. The voltage proportional to the con-

verter’s output current is sensed and amplified by the

precision current sense amplifier of the chip. The

onboard current sense amplifier has a gain of 8 and is in-

tended for differential sensing of the shunt voltage with a

common mode voltage range from 0V up to 5V. The out-

put of the current sense amplifier, CSO is 1V for zero in-

put which guarantees that the circuit can control currents

down to 0A.

The CSO signal is fed to the CA– input of the current er-

ror amplifier through a resistor. The current error ampli-

fier takes the VAO and CSO signals and generates the

error signal for the pulse width modulator.

APPLICATION INFORMATION