UCC2839_13 Datasheet, PDF (1/7 Pages) Texas Instruments – Secondary Side Average Current Mode Controller

UCC2839
UCC3839
Secondary Side Average Current Mode Controller
FEATURES
• Practical Secondary Side Control of
Isolated Power Supplies
• Provides a Self Regulating Bias
Supply From a High Input Voltage
Using an External N-Channel
Depletion Mode FET
• Onboard Precision, Fixed Gain,
Differential Current Sense Amplifier
• Wide Bandwidth Current Error
Amplifier
• 5V Reference
• High Current, Programmable Gm
Amplifier Optimized to Drive
Opto-couplers
DESCRIPTION
The UCC3839 provides the control functions for secondary side average
current mode control in isolated power supplies. Start up, pulse width mod-
ulation and MOSFET drive must be accomplished independently on the
primary side. Communication from secondary to primary side is antici-
pated through an opto-isolator.
Accordingly, the UCC3839 contains a fixed gain current sense amplifier,
voltage and current error amplifiers, and a Gm type buffer/driver amplifier
for the opto-isolator. Additional housekeeping functions include a precision
5V reference and a bias supply regulator.
Power for the UCC3839 can be generated by peak rectifying the voltage of
the secondary winding of the isolation transformer. From this unregulated
voltage, the UCC3839’s bias supply regulator will generate its own 7.5V
bias supply using an external, N-channel, depletion mode FET.
The UCC3839 can be configured for traditional average current mode con-
trol where the output of the voltage error amplifier commands the current
error amplifier. It can also be configured for output voltage regulation with
average current mode short circuit current limiting, employing two parallel
control loops regulating the output voltage and output current independ-
ently.
BLOCK DIAGRAM
SLUS179A - APRIL 1999 - REVISED NOVEMBER 2001
UDG-97011