UBA2033 datasheet(12/20 Pages) PHILIPS

12 / 20 page

2002 Oct 08

Philips Semiconductors

Product speciﬁcation

HF full bridge driver IC

UBA2033

Additional application information

GATE RESISTORS

At ignition of an HID lamp, a large EMC spark occurs. This

can result in a large voltage transient or oscillation at the

gates of the full bridge MOSFETs (LL, LR, HR and HL).

When these gates are directly coupled to the gate drivers

(pins GHR, GLR, GHL and GLL), voltage overstress of the

driver outputs may occur. Therefore it is advised to add a

resistor with a minimum value of 100

Ω in series with each

gate driver to isolate the gate driver outputs from the actual

power MOSFETs gate.

’Dead time’ can also be adjusted via the combination gate

resistor and gate-source capacitance.

GATE CHARGE AND SUPPLY CURRENT AT HIGH FREQUENCY

USE

The total gate current needed to charge the gates of the

power MOSFETs equals:

Where:

Igate = gate current

fbridge = bridge frequency

Qgate = gate charge.

This current is supplied via the internal low voltage supply

(VDD). Since this current is limited to 11 mA (see

“Characteristics” table note 1), at higher frequencies and

with MOSFETs having a relative high gate charge, this

maximum VDD supply current may not be sufficient

anymore. As a result the internal low voltage supply (VDD)

and the gate drive voltage will drop resulting in an increase

of the higher resistance (Ron) of the full bridge MOSFETs.

In this case an auxiliary low voltage supply is necessary.

gate

bridge

gate

UBA2033 Datasheet(PDF) 12 Page - NXP Semiconductors