LM5104 Waveforms

Operational Description

ADAPTIVE SHOOT-THROUGH PROTECTION

LM5104 is a high voltage, high speed dual output driver

designed to drive top and bottom MOSFET’s connected in

synchronous buck or half-bridge configuration, from one ex-

ternally provided PWM signal. LM5104 features adaptive

delay to prevent shoot-through current through top and bot-

tom MOSFETs during switching transitions. Referring to the

timing diagram Figure 3, the rising edge of the PWM input

(IN) turns off the bottom MOSFET (LO) after a short propa-

gation delay (t

the bottom gate voltage (LO) and triggers a programmable

delay generator when the LO pin falls below an internally set

threshold (

≈ Vdd/2). The gate drive of the upper MOSFET

(HO) is disabled until the deadtime expires. The upper gate

is enabled after the TIMER delay (t

MOSFET turns-on. The additional delay of the timer pre-

vents lower and upper MOSFETs from conducting simulta-

neously, thereby preventing shoot-through.

A falling transition on the PWM signal (IN) initiates the turn-

off of the upper MOSFET and turn-on of the lower MOSFET.

A short propagation delay (t

upper gate voltage begins to fall. Again, the adaptive shoot-

through circuitry and the programmable deadtime TIMER

delays the lower gate turn-on time. The upper MOSFET gate

voltage is monitored and the deadtime delay generator is

triggered when the upper MOSFET gate voltage with respect

to ground drops below an internally set threshold (

≈ Vdd/2).

The lower gate drive is momentarily disabled by the timer

and turns on the lower MOSFET after the deadtime delay

expires (t

20089005

FIGURE 3. Application Timing Waveforms

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