The LTC1698 is a precision secondary-side forward converter controller that synchronously drives external N-channel MOSFETs. It is designed for use with the LT3781 primary-side synchronous forward converter controller to create a completely isolated power supply. The LT3781 synchronizes the LTC1698 through a small pulse transformer and the LTC1698 drives a feedback optocoupler to close the feedback loop. Output accuracy of ±0.8% and high efficiency over a wide range of load currents are obtained. The LTC1698 provides accurate secondary-side current limit using an external current sense resistor. The input voltage at the MARGIN pin provides ±5% output voltage adjustment. A power good flag and overvoltage input are provided to ensure proper power supply conditions. An auxiliary 3.3V logic supply is included that supplies up to 10mA of output current.
The LTC1698 provides a secondary‑side solution for isolated forward converters, delivering up to 0.8 % output voltage accuracy and high efficiency over a wide load range. It works with the LT3781 primary‑side controller to form a fully isolated power supply, offering features such as programmable current‑limit protection, over‑voltage fault protection, and a 3.3 V auxiliary logic supply.
The device includes dual N‑channel MOSFET drivers, optocoupler feedback, and a range of pins for synchronization, voltage monitoring, and power‑good signaling. It is offered in 16‑lead SSOP and SO packages and is suitable for industrial control, telecommunications, and automotive power systems.
| Supply Voltage (Vpp) | 6 V – 12.6 V |
|---|---|
| Input Voltage Range (MARGIN, Vep, OVPIN, Isysenp) | -0.3 V to 5.3 V |
| Operating Temperature Range | -40 °C to 85 °C |
| Lead Temperature (Soldering, 10 s) | 300 °C |
An external 4.7 µF bypass capacitor is required on the Vpp pin.