5

9122F–AUTO–03/10

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

(V

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

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

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.