L9908 datasheet(95/153 Pages) STMICROELECTRONICS

95 / 153 page

Figure 70. ON State Diagnosis simplified block diagram

Threshold configuration

The reference thresholds for the OND unit V_ond_th are generated through two 6-bit Current Steering DAC, one

for HS and one for LS FETs.

Diagnosis thresholds can be configured through dedicated SPI bits as follows:

VOND_TH_HS=ΔLSB×VDS_HS_TH5:0

(22)

VOND_TH_LS=ΔLSB×VDS_LS_TH5:0

(23)

Where: ΔLSB is the minimum voltage step and VDS_HS_TH/VDS_LS_TH [5:0] in the register GEN_CFG2 there

are the dedicated SPI configuration bits.

Default value is VDS_HS_TH = VDS_LS_TH = 0x00. The default code equals the first non-zero code 0x01 which

corresponds to a Vond_hs_th = 1LSB = 27 mV

Blanking and Filtering

The OND fault detection is based on the correlation between Vds voltage with the current conducted through

ohm`s law; it turns out that a correct detection can be performed only when Ext. FET is in full RdsON mode.

In order to prevent spurious short circuit detections due to an internal circuit voltage compression, the n-th OND

monitor circuit is masked by the VDH UV diagnosis assertion. During a VDH UV condition OND fault detection is

always prevented.

In order to prevent spurious short circuit detections due to a non-linear operation region, the n-th OND monitor

circuit is masked according to the internal n-th gate drive signal:

•

masking is removed after a programmable blanking time T_ond_blank from gate drive signal rising edge;

•

masking is re-activated soon after gate drive signal falling edge.

The T_ond_blank can be configured by dedicated SPI bits as follows:

Table 89. OND blanking time configuration bits

OND_BLANK2

OND_BLANK1

OND_BLANK0

Description

T_ond_blank = 0.7 μs

T_ond_blank = 1 μs

T_ond_blank = 1.5 μs (Default)

T_ond_blank = 2 μs

T_ond_blank = 2.5 μs

L9908

On State Diagnosis (OND)

DS13546 - Rev 3

page 95/153

L9908 датащи(PDF) 95 Page - STMicroelectronics