Secondary Side Average Current Mode Controller

UC1826

UC2826

UC3826

FEATURES

•

Practical Secondary Side Control of

Isolated Power Supplies

•

1MHz Operation

•

Tailored Loop Bandwidth Provides

Excellent Noise Immunity

•

Voltage Feedforward Provides

Superior Transient Response

•

Accurate Programmable Maximum

Duty Cycle

•

Multiple Chips Can be Synchronized

to Fastest Oscillator

•

Wide Gain Bandwidth Product

(70MHz, Acl>10) Current Error

Amplifier

•

Up to Ten Devices Can Easily Share

a Common Load

DESCRIPTION

The UC1826 family of average current mode controllers accurately

accomplishes secondary side average current mode control. The sec-

ondary side output voltage is regulated by sensing the output voltage

and differentially sensing the AC switching current. The sensed output

voltage drives a voltage error amplifier. The AC switching current, mon-

itored by a current sense resistor, drives a high bandwidth, low offset

current error amplifier. The output of the voltage error amplifier can be

used to drive the current amplifier which filters the measured inductor

current. Fast transient response is accomplished by utilizing voltage

feedforward in generating the PWM ramp.

The UC1826 features load share, oscillator synchronization, undervolt-

age lockout, and programmable output control. Multiple chip operation

can be achieved by connecting up to ten UC1826 chips in parallel. The

SHARE bus and CLKSYN bus provide load sharing and synchroniza-

tion to the fastest oscillator respectively. With its tailored bandwidth, the

UC1826 provides excellent noise immunity and is an ideal controller to

achieve high power, secondary side average current mode control.

7/95

BLOCK DIAGRAM

UDG-95013

Pin Numbers refer to 24-pin packages.