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4670C–BCD–09/05
T6817
3.2 Power-supply Fail
In case of over- or undervoltage at pin VS, an internal timer is started. When the undervoltage
delay time (tdUV, tdOV) programmed by the SCT bit is reached, the power supply fail bit (PSF) in
the output register is set and all outputs are disabled. When normal voltage is present again, the
outputs are enabled immediately. The PSF bit remains high until it is reset by the SRR bit in the
input register.
3.3 Open-load Detection
If the open-load detection bit (OLD) is set to low, a pull-up current for each high-side switch and
a pull-down current for each low-side switch is turned on (open-load detection current IHS1-3,
ILS1-3). If VVS-VHS1-3 or VLS1-3 is lower than the open-load detection threshold (open-load condi-
tion), the corresponding bit of the output in the output register is set to high. Switching on an
output stage with the OLD bit set to low disables the open-load function for this output. If bit SI is
set to low, the open-load function is also switched off.
3.4 Overtemperature Protection
If the junction temperature exceeds the thermal prewarning threshold, TjPW set, the temperature
prewarning bit (TP) in the output register is set. When the temperature falls below the thermal
prewarning threshold, TjPW reset, the bit TP is reset. The TP bit can be read without transferring a
complete 16-bit data word: with CS = high to low, the state of TP appears at pin DO. After the
microcontroller has read this information, CS is set high and the data transfer is interrupted with-
out affecting the state of the input and output registers.
If the junction temperature exceeds the thermal shutdown threshold, Tj switch off, the outputs are
disabled and all bits in the output register are set high. The outputs can be enabled again when
the temperature falls below the thermal shutdown threshold, Tj switch on, and when a high has
been written to the SRR bit in the input register. Thermal prewarning and shutdown threshold
have hysteresis.
3.5 Short-circuit Protection
The output currents are limited by a current regulator. Current limitation takes place when the
overcurrent limitation and shutdown threshold (IHS1-3, ILS1-3) are reached. Simultaneously, an
internal timer is started. The shorted output is disabled when during a permanent short the delay
time (tdSd) programmed by the short-circuit timer bit (SCT) is reached. Additionally, the short-cir-
cuit detection bit (SCD) is set. If the temperature prewarning bit TP in the output register is set
during a short, the shorted output is disabled immediately and SCD bit is set. By writing a high to
the SRR bit in the input register, the SCD bit is reset and the disabled outputs are enabled.
3.6 Inhibit
There are two ways to inhibit the T6817:
1. Set bit SI in the input register to zero
2. Switch pin 5 (INH) to 0V
In both cases, all output stages are turned off but the serial interface stays active. The output
stages can be activated again by bit SI = 1 and by pin 5 (INH) switched back to 5V.