L6706 datasheet(35/47 Pages) STMICROELECTRONICS

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L6706

Output voltage monitor and protections

Doc ID 15698 Rev 2

35/47

15.3

Over voltage and programmable OVP

Once VCC crosses the turn-ON threshold and the device is enabled (OUTEN = 1), L6706

provides an over voltage protection: when the voltage sensed by VSEN overcomes the OVP

threshold (OVPTH), the controller:

–

Permanently turns OFF the high-side MOSFETs.

–

Permanently turns ON the low-side MOSFET in order to protect the load.

–

Drives the OSC/ FAULT pin high (3.3 V typ).

–

Power supply or OUTEN pin cycling is required to restart operations.

The OVP threshold can be also programmed through the OVP pin: leaving the pin floating, it

is internally pulled-up and the OVP threshold is set to VID + 175 mV (typ).

Connecting the OVP pin to SGND through a resistor ROVP, the OVP threshold becomes the

voltage present at the pin. Since the OVP pin sources a constant IOVP = 20 µA (Min) current

(see Table 5), the programmed voltage becomes:

Filter OVP pin with 100 pF (max) vs. SGND.

Over voltage protections is always active during the soft-start, as shown in the following

picture:

Figure 19.

OVP threshold during soft-start for tracking (left) and fixed (right) mode

15.4

Overcurrent protection

The device limits the peak the inductor current entering in constant current until setting UVP

as below explained.

The over current threshold has to be programmed, by designing the ROCSET resistors as

shown in the Figure 20, to a safe value, in order to be sure that the device doesn't enter

Table 8.

Over voltage protection threshold

OVP pin

Thresholds

OVP threshold

Floating

Tracking

OVPTH = VID + 175 mV (typ)

ROVP to SGND

Fixed

OVPTH = ROVP * 20 μA (min)

OVP

μAMIN )

()

⋅

OVP

μAMIN )

()

----------------------------------

⇒

OUTEN

SS_END

VOUT

1.240V

OVPTH

VID+150mV(MIN)

OUTEN

SS_END

VOUT

ROVP * 22uA(MIN)

OVPTH

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