Datasheet

UCC28610

SLUS888F –JANUARY 2009–REVISED SEPTEMBER 2012

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Ferrite Chip or Bead Solution

The ferrite chip or bead connected to the gate of the HVMOSFET provides the best result because it suppresses

ringing in the gate, source, and drain circuits of the HVMOSFET with minimal added losses. Select the ferrite

chip for its resistance value in the ringing frequency range (for example, 60 Ω at 100 MHz). The peak current

rating of the ferrite chip or bead must be sufficient for the drain – gate discharge current that occurs during the

turn-off transient. Excessively large bead reactance can result in low frequency surges of VGG at peak load.

Normally, good results can be achieved with a 0603 ferrite chip device.

DRV Capacitor Solution

A capacitor between DRV and GND can reduce ringing on VGG. Select the DRV capacitor experimentally by

observing the effect on the VGG pin during the first turn-off edge and during the turn-off edge at full load

operation. The capacitor should be less than 3.3 nF so that it does not significantly reduce efficiency. Use a

capacitor with a low Q, such as one with Y5V dielectric. This technique will not completely damp the ringing yet it

can provide sufficient protection against stray inductance between the source of the HVMOSFET and the DRV

pin.

Gate Turn-Off Resistor Solution

A gate turn-off resistor in the range 0 Ω < R

G-OFF

< 5 Ω can damp ringing. The turn-off resistance is limited in

order to prevent the stray source inductance of the HVMOSFET from over charging VGG through the body diode

of the HS Drive MOSFET, in addition to any peak current error problems that would be caused by additional

delay. The damping effect of the gate resistor works better in applications with low current and small source

inductance.

A much larger resistance can be tolerated during the HVMOSFET turn-on transition due to DCM operation. The

recommended turn-on resistance range is 0 Ω <R

G-ON

< 200 Ω in order to prevent the turn-on delay from

interfering with valley switching.

Thermal Shutdown

The UCC28610 protects itself from overheating with an internal thermal shutdown circuit. If the junction

temperature exceeds the thermal shutdown point, T

, the UCC28610 initiates a shutdown event and permits

retry after the retry time, t

RETRY

. Shutdown/Retry cycles continue if the junction temperature is not less than T

minus T

SD_HYST

Product Folder Links: UCC28610