UCC28056CDBVT datasheet(44/55 Pages) TI2

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UCC28056

SLUSD37E – OCTOBER 2017 – REVISED NOVEMBER 2019

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10 Power Supply Recommendations

To operate UCC28056 must be powered from an external VCC supply voltage of 11 V to 34 V. To limit package

dissipation ensure that the supply voltage is not higher than 12 V. Locally decouple the VCC supply with a

capacitor of at least 1 µF connected between the VCC and GND pins using short PCB traces. The controller may

consume current from the VCC rail for a significant period of time; the exact duration depends upon Line and

load, before the output voltage (VOut) reaches regulation. The supply used to power the UCC28056 must be able

to source this energy during the period that output voltage attains regulation.

11 Layout

11.1 Layout Guidelines

11.1.1 VOSNS Pin

Locate the ROS2 and COS2 components adjacent to the VOSNS pin along with the lowest resistor(s) that comprise

ROS1. High voltage drops across the resistor(s) that comprise ROS1. Allow adequate spacing around the high-

voltage nodes that connect to and within ROS1 to avoid air discharge across the PCB surface.

11.1.2 ZCD/CS Pin

Switching edge spikes imposed on the signal feeding this pin may cause the internal ESD structures to conduct,

causing a voltage offset to appear on the capacitive divider feeding this pin. To limit this risk, place the voltage

divider close to the ZCD/CS pin and far from the region of fast changing magnetic field. See the shaded area

show in Figure 37. Maintain a small number of nets between the resistors and capacitors in the divider to limit

capacitive pickup within the divider chain. Maintain the loop identified in Figure 36 small and contain the

minimum area to limit magnetic pickup. Run the connections between the current sense resistor and UCC28056

directly to the terminals of resistor and not be shared with power circuit traces.

When laying out the PCB start with the ZCD/CS pin divider placement and routing to ensure that the needs of

this pin come first.

11.1.3 VCC Pin

A local decoupling capacitor should be connected directly between the VCC and GND pins via short, dedicated,

PCB traces. This capacitor supplies the high current pulses needed to charge the gate capacitance of the power

MOSFET.

11.1.4 GND Pin

Be sure to separate the PCB traces for the GND net of the UCC28056 far from the power circuit GND net.

Connect the GND pin of the UCC28056 device to the power circuit GND at only one terminal of the current

sense resistor. This connection method ensures that the voltage between the UCC28056 device GND pin and

the ZCD/CS pins remains equal to the voltage across the current sense resistor during the MOSFET conduction

period.

11.1.5 DRV Pin

Avoid placing the DRV pin traces close to other high-impedance nets such as ZCD/CS or VOSNS. The fast rising

and falling edges associated with the waveform on this pin may capacitively couple onto these high impedance

nets causing disturbance near the switching edges.

11.1.6 COMP Pin

Locate the RC network attached to this pin close to the pin. Return to the GND pin should be via a short PCB

trace.

11.2 Layout Example

UCC28056CDBVT Datasheet(PDF) 44 Page - Texas Instruments

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