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AS8520

Preliminary Data Sheet - D e t a i l e d D e s c r i p t i o n

Figure 5. Window Watchdog Trigger

7.1.7 Resistive Divider

The resistive divider acts as a battery voltage attenuator. The output of this resistive divider can be connected to an ADC for monitoring the

battery voltage. The division ratio of resistive divider is 21 but can be set also to 481 as a factory programming option. Both divider options can

be disabled in standby mode using the EN signal. Reverse polarity protection of VBAT pin is provided.

7.1.8 HV Low Side Relay Driver Switches

Two NMOS open drain relay driver devices provide over voltage protection. The Driver is disabled if the MCU software hangs up (watchdog reset

or time out WD for LIN TX). The input to the drivers is given through SPI (Low-side driver data register). If over voltage occurs, the Relay driver

turns off irrespective of the input. The driver stays turned off till the voltage returns back to the normal operating range. An optional control bit

available in the Device configuration register, which can be used to switch off the drivers independently to save power. The relay drivers are

disabled using the SPI.

7.1.9 LIN Transceiver

The transceiver provides short circuit limitation, hardware watchdog and over temperature shut down features. The TX watchdog timer is active

when TX is pulled low (active). As soon as the TX watchdog timeout occurs, the LIN bus is released from dominant state to recessive state. The

LIN transceiver has a pull-up resistor (for the slave node; extra resistor externally for the master node) to the VSUP. A diode protection is

available to protect it from back supply from bus line.

The LIN transmitter has the basic functionality of relaying the data from the micro-controller on to the LIN. The data on the LIN needs to have

controlled slew to have reduced EMI. The receiver relays the data from the LIN to the micro-controller. This transmitter has optimized EMC

performance across different loading conditions conforming to the LIN 2.1 standards. The wake-up detects a wake up event on the LIN.

7.2 Operating Modes and States

The AS8520 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. Refer to Table 14 for a detailed description

on transition for each mode.

7.2.1 Normal Mode

This is the mode after the power-up. In normal mode, LDO, LIN Transceiver, Window Watchdog, Resistive divider and the line drivers are all

turned on. All the blocks are completely functional. LDO is now capable of delivering maximum load current possible as per the device

specifications. The LIN Transceiver is capable of sending the TX data from microcontroller to the LIN bus at a maximum rate of 20Kbps.

Resistive divider is used to attenuate the battery voltage and relay drivers are used to drive the relay. EN signal is set to high and LIN, TX, RX

the diagnostic register, which can be read through the SPI interface.

Period

Non-Service time (WD_TCL)

Service time (WD_TSV)

Trigger

restart

period

Trigger via

SPI

Last trigger point

Earliest possible

trigger point

(System will not

RESET)

latest possible

trigger point

(System wil not be

RESET)

50 %

100 %

Valid Trigger point

(System will not be

RESET)

Unwanted trigger point

(System will be

RESET)