AN2738 datasheet(48/54 Pages) STMICROELECTRONICS

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The below-ground voltage on the OUT pin

AN2738

48/54

Doc ID 14589 Rev 2

Figure 43.

OUT below-ground voltage in transient conditions: limited boot over-

charging

11.4.3

Below-ground voltage spikes

As previously stated, the duration of the dynamic contribution of the below-ground voltage

on the OUT pin is not enough to over-charge the bootstrap capacitor. This fact usually

removes the risk of exceeding the recommended maximum value of 20 V for VBOOT -VOUT

voltage, but it increases the danger of pulling down the BOOT pin below ground, thus

violating its absolute minimum rating. As mentioned above, this phenomenon should be

avoided for safe IC gate driver operation. However, note that applicative bench tests have

shown the L6390

proper operation even with below-ground spikes on the OUT pin well

above - 50 V (see Figure 44).

VOUT

VCC

VBOOT

VBOOT - VOUT

virtual final value

in steady state

VBGV_static

VBGV_spike

VBOOT - VOUT

befor overcharge

VOUT

VBOOT - VOUT

safe operating

maximum range

(20V)

VBOOT - VOUT

real

overcharge

High side OFF time

HIN

AN2738 Datasheet(PDF) 48 Page - STMicroelectronics