ATA6814 Datasheet, PDF (18/29 Pages) ATMEL Corporation – Automotive Failsafe System IC

7. Functional Description
7.1 Bandgaps
For voltage monitoring and as references for various voltage regulators, two independent band-
gaps are used. The bandgaps for the generation and monitoring of the internal supply (V5 and
V5A) are used in cross-over mode.
7.2 Bias
The external resistor at RREF defines a current reference for all blocks and determines main
oscillator frequency. The current through the external resistor is monitored and in case of mal-
function (pin open or short to ground; current is less than 0.25 times or greater than 8 times
nominal value), a bias failure is detected (see Table 7-9 on page 25).
7.3 Temperature Monitoring
To protect the circuit from extensive temperature in error condition, two temperature levels are
implemented to switch off various blocks. At the lower temperature level, the outputs WLN,
OUTN or OUTP are switched off after a debounce time, if the corresponding driver is in current
limitation.
The Warning Lamp is switched on above the upper temperature level. All other drivers and the
linear regulators will switch off. If the temperature level falls below the shutdown temperature
(hysteresis), all drivers except TCFET and the relay drivers will go to their previous state.
7.4 Enable/Standby
The power consumption of ATA6814 is reduced to a minimum via inputs E5 or EK15 (sleep
mode). With the signal TEN via SPI command, the inputs E5 and EK15 can be overwritten and
the ATA6814 will stay active (keep-alive function). The status of EK15 can be read via SPI.
Table 7-1.
E5
High
x
Low
Low
Enable/Standby Table
EK15
x
High
Low
Low
TEN (SPI)
x
x
High
Low
ATA6814
Active
Active
Active
Standby
7.5 V12 Voltage Monitoring
The system supply is checked for overvoltage and undervoltage at the internal voltage divider. If
the voltage exceeds the limits, the drivers are switched off and a reset at RESN and RESAN is
generated (see Table 7-9 on page 25).
18 ATA6814 [Preliminary]
4849B–AUTO–09/05