L6935TR datasheet(12/20 Pages) STMICROELECTRONICS

12 / 20 page

Device description

L6935

12/20

5.2

Power Good

L6935 presents a PGOOD flag, an open drain output that is grounded during all the soft

start procedure, and is left free when VOUT reaches 90 % of the programmed value.

An hysteresis of 10 % is also provided in order to avoid false triggering due to the noise

generated by the application. Figure 10 shows the PGOOD commutations.

Figure 10.

Power good window

5.3

VIN vs VBIAS

L6935 provides the flexibility to supply the internal logic (VBIAS) with a supply different than

the power input (VIN). The aim of this feature is to provide low-drop regulation still having

the supply voltage to correctly drive the internal power mosfet so optimizing the conversion.

VIN drives only the drain of the power DMOS and it can be kept as low as possible

(VIN > VOUT + VDROPmin), while VBIAS drives the control section. VBIAS must be typically

higher than VIN.

5.4

Protections

L6935 is equipped with a set of protections in order to protect both the load and the device

from electrical overstress. Each protection does not latch the device, that returns to work

properly as the perturbation disappear.

5.4.1

Over-current protection

An over current protection is provided: if the current that flows through the power DMOS is

greater than 3.5 A, the device adjust the power DMOS driving voltage in order to keep

constant the delivered current (IOUT). Anyhow the output may drop also causing the

PGOOD to be set low.

Figure 11 show the way the OCP intervention: as the threshold value is reached by IOUT, the

device forces a lower output current (~3.5 A).

L6935TR Datasheet(PDF) 12 Page - STMicroelectronics