PC33879EKSLASHR2 datasheet(14/20 Pages) MOTOROLA

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33879

MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

MCU INTERFACE DESCRIPTION

Introduction

The 33879 is an 8-output hardware-configurable power

switch with 16-bit serial control. A simplified block diagram of

the 33879 is shown in Figure 1 on page 2.

The 33879 device uses high-efficiency up-drain power

DMOS output transistors exhibiting low drain-to-source ON

resistance (RDS(ON) = 1.0 Ω at 25°C typical) and dense CMOS

control logic. All outputs have independent voltage clamps to

provide fast inductive turn-off and transient protection.

In operation, the 33879 functions as an 8-output serial switch

serving as a 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. This device directly interfaces to an MCU using a SPI

for control and diagnostic readout. Figure 13 illustrates the

basic SPI configuration between an MCU and one 33879.

Figure 13. SPI Interface with Microcontroller

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

levels and incorporate positive logic. When a SPI bit is

programmed to a logic [0], the corresponding output will be

OFF. Conversely, when a SPI bit is programmed to logic [1] the

output being controlled will be ON. Diagnostics are treated in a

similar manner. Outputs with a fault will feed back (via DO) a

logic [1] to the microcontroller, while normal operating outputs

will provide a logic [0].

Figure 14 illustrates the daisy chain configuration using the

33879. Data from the MCU is clocked daisy chain through each

device while the CS bit is commanded low by the MCU. During

each clock cycle, output status from the daisy chain is

transferred to the MCU via the Master In Slave Out (MISO) line.

On rising edge of CS, command data stored in the input register

is then transferred to the output driver.

Figure 14. 33879 SPI System Daisy Chain

Multiple 33879 devices can be controlled in a parallel input

fashion using the SPI. Figure 15 illustrates the control of

24 loads using three dedicated parallel MCU ports for chip

select.

Figure 15. Parallel Input SPI Control

Receive

Buffer

Parallel

Ports

Logic

33879

MC68HCxx

Microcontroller

SCLK

MISO

MOSI

Shift Register

16 Bits

MC68HCxx

Microcontroller

with

SPI Interface

8 Outputs

MISO

MOSI

Parallel Port

SCLK

33879

SCLK

Parallel

Ports

MOSI

MISO

SCLK

8 Outputs

MC68HCxx

Microcontroller

with

SPI Interface

33879

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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