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AS8525

Datasheet - Application In form atio n

8 Application Information

The AS8525 chip consists of a programmable gain amplifier, a resistive divider, two low drop-out regulators, and a LIN bus transceiver.

Additionally integrated are a RESET unit with a power-on-reset delay and programmable window watchdog and timeout watchdog timers. It also

includes a watchdog time-out on LIN TX node to indicate if the Microcontroller is stuck in a loop and the LIN bus remains in dominant time for

more than the necessary time.

8.1 Operating Modes and States

The device provides four main operating modes ‘normal’, ‘sleep/stand-by’ (programmed by OTP), “temporary shutdown” and ‘thermal shutdown’.

The LIN transceiver can be programmed to operate with lower slew in the normal mode. A detailed state transition table is shown in the following

section (see Table 16).

8.1.1 Normal Mode

This is the mode after the power-up. In this mode, voltage regulators, LIN transceiver, window Watchdog are all active. The PGA and resistive

divider can be enabled through SPI. LIN transceiver is capable of sending the TX data from micro-controller to the LIN bus at a maximum rate of

20Kbps.

8.1.2 Standby Mode

Standby mode is a functional low-power mode and is entered by pulling EN to ground. The LIN transceiver, PGA, resistive divider, window

watchdog, and TX timeout watchdog circuits are disabled. But, it is possible to selectively enable the voltage and current measurement paths in

this mode using an externally generated measurement enable (MEN) signal on the MEN pin. The timeout Watchdog can be enabled in this mode

to make sure that the Microcontroller is active.

8.1.3 Sleep Mode

Sleep mode is the current saving mode. The voltage regulators are disabled in this mode. Also, the PGA, resistive divider, LIN transceiver, and

the reset and Watchdog units are switched off. The LIN wake-up circuit and oscillator are active. Wake-up is possible only through remote wake-

up through LIN pin pulling it to dominant state for 100us.

8.1.4 Temporary Shutdown Mode

In this mode, the regulators are powered down and the VCC, AVCC are pulled down. This provides an alternative way to reset those components

powered by AS8525. The feature has to be enabled by an OTP bit and can be invoked through SPI. The LIN transceiver along with the LIN

wake-up circuit is powered down. No remote wake-up functionality is possible. LIN bus enters into recessive state. The system goes out of this

mode to normal mode after the timeout of an internal timer.

8.1.5 Thermal Shutdown Mode

mode.