Rainbow Electronics ATA6834 - Manual (Page 5)

5
9122B–AUTO–10/08
ATA6833/ATA6834 [Preliminary]
3. Functional Description
3.1 Power Supply Unit with Supervisor Functions
3.1.1 Power Supply
The IC has to be supplied by a reverse-protected battery voltage. To prevent damage to the IC,
proper external protection circuitry has to be added. It is recommended to use at least one
capacitor combination of storage and RF capacitors behind the reverse protection circuitry,
which is connected close to the VBAT and GND pins of the IC.
A fully integrated low-power and low-drop regulator (VINT regulator), stabilized by an external
blocking capacitor, provides the necessary low-voltage supply needed for the wake-up process.
A trimmed low-power band gap is used as reference for the VINT regulator as well as for the
VCC regulator. All internal blocks are supplied by VINT regulator. VINT regulator must not be
used for any external supply purposes.
Nothing inside the IC except the logic interface to the external microcontroller is supplied by the
5V/3.3V VCC regulator.
Both voltage regulators are checked by a “power-good comparator”, which keeps the whole chip
in reset as long as the internal supply voltage (VINT regulator output) is too low and generates a
reset for the external microcontroller if the output voltage of the VCC regulator is not sufficient.
3.1.2 VBatt Switch
This high-voltage switch provides the battery voltage at pin VBATSW for various purposes. It is
switched ON after power on reset when the IC transits to Active Mode and it will only turn OFF
when the IC changes to Sleep Mode. Watchdog resets do not have an effect on the switch. The
switch can be used for measuring purposes as well as to switch on external voltage regulators.
3.1.3 Voltage Supervisor
This function is implemented to protect the IC and the external power MOS transistors from
damage due to overvoltage on PBAT input. In the event of overvoltage (V
THOV
) or undervoltage
(V
THUV
), the external NMOS motor driver transistors will be switched off. The failure state will be
flagged on DG2 pin. It is recommended to block PBAT with an external RF capacitor to suppress
high frequency disturbances.
3.1.4 Temperature Supervisor
An integrated temperature sensor prevents the IC from overheating. If the temperature is above
the overtemperature pre-warning threshold T
JPW set
, the diagnostic pin DG3 will be switched to
HIGH to signal this event to the external microcontroller. The microcontroller should take actions
to reduce the power dissipation in the IC. If the temperature rises above the overtemperature
shutdown threshold T
J switch off
, the VCC regulator and all output drivers together with the LIN
transceiver will be switched OFF immediately and the /RESET signal will go LOW. Both thresh-
olds have a built-in hysteresis to avoid oscillations. The IC will return to normal operation (Active
Mode) when it has cooled down below the shutdown threshold. When the junction temperature
drops below the pre-warning threshold, bit DG3 will be switched LOW.