The UCC3752 controller is designed for driving a power stage that generates low frequency, high voltage sinusoidal signals for telephone ringing applications. The controller and the power stage are most suitable for up to 5 line applications where low cost, high efficiency and minimum parts count are critical. A semi-regulated DC voltage is added as an offset to the ringing signal. The ring generator operation is non-isolated and open loop.
The UCC3752 directly drives primary side switches used to implement a push-pull resonant converter topology and transformer coupled sampling switches located on the secondary of the converter. For normal ring signal generation, the primary switching frequency and secondary sampling frequency are precisely offset from each other by the ringing frequency to produce a high voltage low frequency alias signal at the output. The off-hook condition is detected by sensing the AC current and when AC limit is exceeded, a flag is generated on the OFFHOOK pin.
The drive signal frequencies are derived from a high frequency (3579545 Hz) crystal. The primary switching frequency is 89.489 kHz and the sampling frequency is 20, 25 or 50 Hz less depending on the status of frequency select pins FS0 and FS1.
Novel Topology for Low-Cost, Efficient Generation of Ring Voltage
Suitable for Multi-Line Operation
Selectable 20, 25 and 50 Hz Ring Frequency
Secondary (AC) Current Limiting Generates an Off-Hook Detect Signal
Primary Current Limiting to Turn Power Stage Off Under Fault Conditions
Operates from a Single 12V Supply
The circuits described in this datasheet are covered under US Patent #5,663,878 and other patents pending.
