Analog Integrated Circuit Device Data

Freescale Semiconductor

11

33996

FUNCTIONAL DESCRIPTION

OPERATIONAL MODES

OPERATIONAL MODES

On each SPI communication, a 24-bit command word is

sent to the 33996 and 24-bit fault word is received from the

33996. The Most Significant Bit (MSB) is sent and received

first.

Command Register Definition:

0 = Output Command Off

1 = Output Command On

SO Definition:

0 = No fault

1 = Fault

MCU INTERFACE DESCRIPTION

In operation the 33996 functions as a 16-output serial

switch serving as a microcontroller (MCU) bus expander and

buffer with fault management and fault reporting features. In

doing so, the device directly relieves the MCU of the fault

management functions.

The 33996 directly interfaces to an MCU and operates at

system clock serial frequencies up to 6.0 MHz using a Serial

Peripheral Interface (SPI) for control and diagnostic readout.

Figure 9 shows the basic SPI configuration between an

MCU and one 33996.

Figure 9. 33996 SPI Interface with Microcontroller

All inputs are compatible with 3.3 V/5.0 V CMOS logic

levels and incorporate positive logic. An input that is

programmed to a logic low state (< 0.8 V) will have the

corresponding output OFF. Conversely, an input

programmed to a logic high state (> 2.2 V) will have the

Table 5. Fault Operation

Serial Output (SO) Pins Reports

Overtemperature

Fault reported by Serial Output (SO) pin.

Overcurrent

SO pin reports short to battery/supply or overcurrent condition.

Output “ON’ Open Load Fault

Not reported.

Output “OFF’” Open Load Fault

SO pin reports output “OFF’” open load condition.

Device Shutdowns

Overvoltage

Upon recovery all outputs assume previous state or OFF based on the Overvoltage bit in the Global

Shutdown/Retry Control Register.

Overtemperature

Only the output experiencing an overtemperature fault shuts down. Output may auto-retry or remain

off according to the control bits in the Global Shutdown/Retry Control Register.

Overcurrent

Output will remain in current limit 0.9 A to 2.5 A until thermal limit is reached. When thermal limit is

reached, device will enter overtemperature shutdown. Output will operate as programmed in the

Global Shutdown/Retry Control Register. Fault flag in SO Response word will be set.

33996

MC68HCXX

Microcontroller

Receive

Buffer

Parallel

Ports

To Logic

24-Bit Shift Register

Shift Register

MOSI

SI

MISO

SO

SCLK

RST

CS

PWM