Open-loop LLC transformer driver for isolated bias supplies


Product details


Topology Resonant LLC Duty cycle (Max) (%) 50 UVLO thresholds on/off (V) 8.5/8 Features Adjustable Switching Frequency, Current Limiting, Enable/Shutdown, Resonant, Soft Start, Thermal Shutdown Operating temperature range (C) -40 to 125 Rating Catalog open-in-new Find other PWM controllers & resonant controllers

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  • Open-loop LLC transformer driver
  • Ultra-low EMI
  • Supply range: 9 V to 34 V
  • Output power: 6-W with 24-V input
  • Resistor programmable switching frequency from 100 kHz to 1.2 MHz
  • Synchronization to external clock
  • Programmable maximum dead-time with automatic dead-time adjustment
  • Undervoltage lockout
  • Adjustable over-current protection threshold
  • External disable function
  • Input over voltage protection
  • Over temperature protection (TSD)
  • Fault-code output for system intelligence
  • Latched and fault-auto-restart versions available
  • 8-Pin DGN package with thermal pad
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The UCC25800-Q1 open-loop LLC transformer driver integrates the switching power stage, the control, and the protection circuits to simplify isolated bias supply designs. The LLC topology allows the design to utilize a transformer with higher leakage inductance, but much smaller parasitic primary-to-secondary capacitance. This low-capacitance transformer design enables an order of magnitude reduction in the common-mode current injection through the bias transformer. This makes the UCC25800-Q1 an ideal solution for the isolated bias supply in various automotive applications to minimize the EMI noise caused by the high speed switching devices. The UCC25800-Q1 operates with soft switching to further reduce the EMI noise.

UCC25800-Q1 has a programmable frequency range of 100 kHz to 1.2 MHz. This high switching frequency reduces the transformer size and footprint, as well as the overall cost of the bias supply. The integrated SYNC function allows the bias supplies in the system to be synchronized with an external clock signal, further reducing the system level noise.

The dead-time of UCC25800-Q1 is adjusted automatically to minimize the conduction loss and simplify the design. The maximum dead-time is programmable to ensure power stage design flexibility.

With the integrated low-resistance switching power stage, the UCC25800-Q1 can achieve a 6-W design with 24-V input. With a fixed input voltage that is above 9 V and below 34 V, the open-loop LLC converter control also helps the output regulation to remain ±5% when the load is above 10%.

The programmable over-current protection (OCP) allows flexibility on the power stage design to minimize the transformer size, further reducing the system cost. The protection features such as adjustable OCP, input OVP, TSD and the protection from pin faults ensure robust operation. A fixed 1.5-ms soft start reduces the inrush current during start-up and fault recovery.

UCC25800-Q1 also provides a dedicated multi-function pin for external disabling, and fault code reporting. The fault code reporting sends the fault code once the bias supply is in the protection mode, allowing the system level controller to make more intelligent decisions during system failure modes.

The UCC25800-Q1 is offered in an 8-pin DGN package with the thermal pad to enhance its thermal handling capability.

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Technical documentation

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Type Title Date
* Data sheet UCC25800-Q1 Open-Loop LLC Transformer Driver for Isolated Bias Supplies datasheet (Rev. A) Jul. 20, 2021
Application note Bias Supply Design for Isolated Gate Driver Using UCC25800-Q1 Mar. 31, 2021
User guide Using the UCC25800EVM-037 2-W LLC Half-Bridge Converter with Pre-Regulator Mar. 12, 2021
Certificate UCC25800EVM-037 EU RoHS Declaration of Conformity (DoC) Dec. 16, 2020

Design & development

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Hardware development

document-generic User guide

This isolated open-loop LLC transformer driver converter is based on the device UCC25800 and has a pair of outputs, +18-V and -5-V, and provides output power up to 2 W from 6-V to 26-V DC input to provide isolated bias power to SiC MOSFET or IGBT gate drivers for traction inverter and industrial (...)

  • UCC25800 2-W LLC converter with 6-V to 26-V dc input and 18-V and 5-V outputs
  • Provide isolated bias power to SiC MOSFET or IGBT gate drivers for traction inverter and industry inverter applications
  • Allow transformer with significant leakage inductance but much less primary-to-secondary capacitance to (...)

Software development

SLUC705.ZIP (604 KB)

Design tools & simulation

SLUM781.ZIP (152 KB) - SIMPLIS Model

Reference designs

Isolated IGBT and SiC driver bias supply reference design for traction-inverter applications
PMP22835 — This isolated open-loop LLC transformer driver converter provides dual +20-V and -4-V outputs up to 6 W for traction inverter applications. The LLC topology allows the transformer to have significant leakage inductance, but a much smaller primary-secondary capacitance, which significantly reduces (...)
document-generic Schematic document-generic User guide

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