Rainbow Electronics ATA6837 - Manual (Page 7)

7
4953C–AUTO–09/07
ATA6837 [Preliminary]
3.2 Power-supply Fail
In case of undervoltage at pin VS, an internal timer is started. When during a permanent under-
voltage the delay time (t
dUV
) 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 I
HS1-6
,
I
LS1-6
). If V
VS
– V
HS1-6
or V
LS1-6
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 OLD bit set to low disables the open load function for this output.
3.4 Overtemperature Protection
If the junction temperature exceeds the thermal prewarning threshold, T
jPW
set, the temperature
prewarning bit (TP) in the output register is set. When the temperature falls below the thermal
prewarning threshold, T
jPW
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, T
j 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, T
j 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 (I
HS1-6
, I
LS1-6
) are reached. Simultaneously, an
internal timer is started. The shorted output is disabled when during a permanent short the delay
time (t
dSd
) 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 ATA6837:
• Set bit SI in the input register to 0
• Switch pin 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 (when INH = VCC) or by pin INH switched back to
VCC (when SI = 1).