March 18, 2014 – Linear Technology Korea (CEO Hong Sa-kwak) announced the release of a synchronous forward controller (Product Name: LT3752/LT3752-1) capable of high input voltages and featuring an active clamp transformer reset function. With VOUT-controlled startup and shutdown, an integrated housekeeping controller supplies bias current to both primary and secondary ICs. Internal bias generation eliminates the need to generate bias power using additional windings, thereby reducing the complexity and size of the main power transformer.

The LT3752 operates over an input voltage range of 6.5V to 100V. For inputs up to 400V and above, the LT3752-1 enables RC startup at input voltages limited to the maximum voltage by selecting only external components, making it ideal for HV/HEV automotive applications. Output voltage regulation of ±5% can be achieved without the use of an optocoupler. If an optocoupler is used, regulation of ±1.5% can be realized.

The LT3752/-1 sends control signals via a pulse transformer to the secondary MOSFET driver for synchronous rectification timing. This product can also be used in self-driven applications (when operating within a narrow input voltage range). In self-driven applications, the secondary MOSFET is controlled by power transformer pulses. When using the LT3752/-1, the secondary IC no longer requires a startup circuit for operation when the output voltage is 0V, so controlled VOUT startup is possible.

The LT3752/-1 includes a precise, programmable volt-second clamp. When the converter is set above its natural duty cycle, this product provides a duty cycle guardrail to limit the primary switch reset voltage and prevent transformer saturation during load transients. The volt-second clamp limits VOUT to a maximum when the optopath is open or when VOUT is defined in alternative opto-free applications. For non-isolated high step-down ratio applications, each IC includes a voltage error amplifier, enabling a very simple, non-isolated, fully regulated synchronous forward converter. Additional features include programmable overcurrent protection and adjustable input undervoltage and overvoltage lockouts with built-in thermal shutdown. The LT3752/-1 provides programmable operating switching frequencies from 100 kHz to 500 kHz and can be synchronized with an external clock, allowing for a wide range of output inductor values and transformer sizes.

The LT3752/-1 is available in a TSSOP-38 package with several pins removed for high-voltage spaces. The LT3752/-1 Class E and Class I versions operate over a junction temperature range of -40°C to 125°C. The LT3752/-1 Class H is guaranteed to operate over an operating junction temperature range of -40°C to 150°C. The LT3752/-1 Class MP is guaranteed to operate over an operating junction temperature range of -55°C to 150°C.

Photo Caption: Active Clamp Synchronous Forward Controller