Rainbow Electronics ATA6824 - Manual (Page 6)

6
4931C–AUTO–09/06
ATA6824 [Preliminary]
5.1.2 Voltage Supervisor
This block is intended to protect the IC and the external power MOS transistors against overvolt-
age on battery level and to manage undervoltage on it.
Function: in case of both overvoltage alarm (V
THOV
) and of undervoltage alarm (V
THUV
) the exter-
nal NMOS motor bridge transistors will be switched off. The failure state will be flagged via DG2.
No other actions will be carried out. The voltage supervision block is connected to VBAT and fil-
tered by a first-order low pass with a corner frequency of typical 15 kHz.
5.1.3 Temperature Supervisor
There is a temperature sensor integrated on-chip to prevent the IC from overheating due to a
failure in the external circuitry and to protect the external NMOSFET transistors.
In case of detected overtemperature (180°C), the diagnostic pin DG3 will be switched to “H” to
signalize this event to the microcontroller. It should undertake actions to reduce the power dissi-
pation in the IC. In case of detected overtemperature (200°C), the V
CC
regulator and all drivers
including the LIN transceiver will be switched OFF immediately and /RESET will go LOW.
Both temperature thresholds are correlated. The absolute tolerance is ±15°C and there is a
built-in hysteresis of about 10°K to avoid fast oscillations. After cooling down below the 170°C
threshold; the IC will go into Active mode.
The serial interface has a separate thermal shutdown with disabled the low-side driver at typi-
cally 200°C.
5.2 5V/3.3V VCC Regulator
The 5V/3.3V regulator is fully integrated on-chip. It requires only a 2.2 µF ceramic capacitor for
stability and has 100 mA current capability. Using the VMODE pin, the output voltage can be
selected to either 5V or 3.3V. Switching of the output voltage during operation is not intended to
be supported. The VMODE pin must be hard-wired to either VINT for 5V or to GND for 3.3V. The
logic HIGH level of the microcontroller interface will be adapted to the VCC regulator voltage.
The output voltage accuracy is in general < ±3%; in the 5V mode with V
VBAT
< 8V it is limited to
< 5%.
To prevent destruction of the IC, the current delivered by the regulator is limited to maximum
160 mA to 320 mA. The delivered voltage will break down and a reset may occur.
Please note that this regulator is the main heat source on the chip. The maximum output current
at maximum battery voltage and high ambient temperature can only guaranteed if the IC is
mounted on an efficient heat sink.
A power-good comparator checks the output voltage of the VCC regulator and keeps the exter-
nal microcontroller in reset as long as the voltage is too low.
5.3 Reset and Watchdog Management
The timing basis of the watchdog is provided by the trimmed internal oscillator. Its period T
OSC
is
adjustable via the external resistor R
WD
.
The watchdog expects a triggering signal (a rising edge) from the microcontroller at the WD
input within a period time window of T
WD
. In order to save current consumption, the watchdog is
switched off during Sleep mode.