IPS160HF datasheet(13/27 Pages) STMICROELECTRONICS

13 / 27 page

6.4

Open load in off-state

The IC provides the open load detection feature which detects if the load is disconnected from the OUT pin. This

feature can be activated by a resistor (RPU) between OUT and VCC pins.

Figure 7. Open load off-state

OUT

PGND

SUPPLY RAIL

GROUND PLANE

Application board

RLOAD

RPU

Open load

detection signal

VOLOFF

VCC

EXPOSED PAD

RLED

In case of wire break and during the OFF state (IN = low), the output voltage VOUT rises according to the

partitioning between the external pull-up resistor and the internal impedance of the IC (130 kΩ < RI < 360 kΩ).

The effect of the LED (if any) on the output pin has to be considered as well. In case of wire break and during the

ON state (IN = high), the output voltage VOUT is pulled up to VCC by the low resistive integrated switch. If the load

is not connected, in order to guarantee the correct open load signalization it must result:

VOUT > VOLoff(max.)

Referring to the circuit in Figure 7. Open load off-state:

VOUT=VCC−RPU×IPU=VCC−RPU× IRI+ILED+IRL

(1)

therefore:

RPU< VCCmin −VOLoffmax

VOLoffmax

RImin +VOLoffmax −VLED

RLED

(2)

If the load is connected, in order to avoid any false signalization of the open load, the following condition must

hold:

VOUT < VOLoff(min)

By taking into account the circuit in figure 6:

VOUT=VCC−RPU×IPU=VCC−RPU× VOUTRI+VOUT−VLED

RLED +VOUTRL

(3)

so:

RPU>

VCCmax −VOLoffmin

VOLoffmin

RImax +VOLoffmin −VLED

RLED +VOLoffmin

(4)

The fault condition is signaled on the DIAG pin and the fault reset occurs when load is reconnected.

If the channel is switched on by the IN pin, the fault condition is no longer detected.

IPS160HF, IPS161HF

Open load in off-state

DS13271 - Rev 2

page 13/27

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