Analog Integrated Circuit Device Data



Freescale Semiconductor

23

33814

If the BATSW output is used to control an LED, the LED cathode should be tied to ground and the LED anode should be

connected to the BATSW pin through an external resistor. The value of the external resistor should be 340 ohms or greater. Care

must be taken if the BATSW output is sent off-board due to the chance of shorts to the battery or shorts to ground, for which the

output is not protected. At a minimum, this output should be protected by a diode, the current limit resistor, and an ESD capacitor

(.01 µF ceramic).

5.1.14 Using ROUT2 as a Power RelAY

The ROUT2 (Relay 2 Output) can be used to drive a power relay. The RIN2 input or the RIN2 bit in the SPI Control register can

be used to turn the ROUT2 output on or off as desired. The BATSW output can be connected to the RIN2 input to control the

power relay, or the MCU can chose to control the RIN2 bit in the SPI Control register to actuate the power relay.

The ROUT2 output is unique in that it can be kept turned on even after KEYSW is turned off (as long as the PWREN bit is still

set to a one) by setting the shut down disable (SDD) bit in the ROUT2 Configuration register.

5.1.15 ISO9141 Transceiver (MTX, MRX, ISO9141)

These three pins are used to provide an ISO914, K-line communication link for the MCU to provide diagnostic support for the

system. MRX is the 5.0 V logic level serial output line to the MCU. MTX is the 5.0 V logic level serial input to the IC from the MCU.

The ISO9141 pin is a bi-directional line, consistent with the ISO9141 specification for signalling to and from the MCU. There is

only one bit in the SPI Status register to indicate an over-temperature fault from the ISO9141 functional block. There are no

Configuration or Control registers associated with this functional block.

5.1.16 Tachometer (TACHOUT)

The TACHOUT pin is a low side driver, that can used to drive a tachometer meter movement. TACHOUT can be programmed

via the SPI to:

1. Output the same signal as VRSOUT divided by a 1 to 32 programmable divider,

2. Output a PWM signal with a frequency and duty cycle programmable via the SPI, or

3. Output one of 8 fixed frequencies as indicated in Table 6.

If a tachometer is not required the TACHOUT output can also be used as a low current, SPI controlled, low side driver to drive a

LED or other low current load. The SPI Configuration register for the Tachometer is used to determine which mode this output

will be used in. The TACHOUT output handles over-current (OC) differently than the other low side drivers. When an over-current

limit is reached the TACHOUT output does not enter a current limiting state but rather shuts the output off to protect the output

device. The retry option works similarly to the other low side drivers.

In the LSD mode bit 4 of the SPI Configuration register controls the turn on or turn off of the Open Load detect current sink.

Table 6. TACHOUT SPI Configuration Register

SPI Configuration

Register 4 Bits 6,5

TACHOUT Mode

00 (default)

VRSOUT divided by ‘N’ where ‘N’ is defined by bits 0 thru 4 of SPI

Configuration Register 4 (1 - 32)

00001 = 1 (default)

.

11111 = 31

00000=32

01

Oscillator Output

10

Low Side Driver (LSD)

11

Same as 10 above