Product Overview

The UC1901 series is engineered to address challenges in closing a feedback control loop across a voltage isolation boundary. Serving as a stable and dependable alternative to optical couplers, these devices employ an amplitude modulation system that enables a loop error signal to be coupled using a small RF transformer or capacitor. The programmable, high-frequency oscillator within the UC1901 series allows for the use of smaller, more cost-effective transformers that can easily meet the isolation requirements of modern line-operated power systems. In addition to RF operation, these devices feature an external clock input that enables synchronization with a system clock or the switching frequency of a SMPS. An added benefit is the status monitoring circuit, which provides an active-low output when the sensed error voltage is within ±10% of the reference. The DRIVERA output, DRIVERB output, and STATUS output remain disabled until the input supply reaches a sufficient level to ensure proper device operation. These devices can also function as a DC driver for optical couplers, offering advantages such as 4.5 to 40V supply operation, a 1% accurate reference, and a high gain general-purpose amplifier, even in applications where an AC system is not desired.

Key Features

• Amplitude-Modulation System for Transformer Coupling of Isolated Feedback Error Signals
• Cost-Effective Alternative to Optical Couplers
• Internal 1% Reference and Error Amplifier
• Internal Carrier Oscillator Capable of Operating up to 5MHz
• Modulator Synchronizable to an External Clock
• Loop Status Monitoring
• Application Guidance
• The error amplifier compensation terminal, Pin 12, is designed to provide feedback to the amplifier's inverting input at Pin 11. In most applications, a series DC blocking capacitor should be included in the feedback network. The amplifier is internally compensated for unity feedback. The waveform at the driver outputs is a squarewave with an amplitude proportional to the error amplifier input signal. There is a fixed 12dB of gain from the error amplifier compensation pin to the modulator driver outputs. The frequency of the output waveform is controlled by either the internal oscillator or an external clock signal. When using the internal oscillator, the squarewave will have a fixed 50% duty cycle. If the internal oscillator is disabled by connecting Pin 1, CR, to VIN, then the frequency and duty cycle of the output will be determined by the input clock waveform at Pin 2. If the oscillator remains disabled and there is no clock input at Pin 2, there will be a linear 12dB of signal gain to one or the other of the driver outputs, depending on the DC state of Pin 2. The driver outputs are emitter followers capable of sourcing a minimum of 15mA of current. The sink current, internally limited at 700µA, can be increased by adding resistors to ground at the driver outputs.