33291L View Datasheet(PDF) - Freescale Semiconductor

Part Name

Description

Manufacturer

33291L

Eight-Output Switch with Serial Peripheral Interface I/O

Freescale Semiconductor 

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

The 33291L was conceived, specified, designed, and

developed for automotive applications. It is an eight-output

low-side power switch having 8-bit serial control. The 33291L

incorporates SMARTMOS technology having CMOS logic,

bipolar/MOS analog circuitry, and independent state of the

art double diffused MOS (DMOS) power output transistors.

Many benefits are realized as a direct result of using this

mixed technology. A simplified block diagram delineates

33291L in Figure 2.

Where bipolar devices require considerable control

current for their operation, structured MOS devices, since

they are voltage controlled, require only transient gate

charging current affording a significant decrease in power

consumption. The CMOS capability of the SMARTMOS

process allows significant amounts of logic to be

economically incorporated into the monolithic design.

Additionally, the bipolar/MOS analog circuits embedded

within the updrain power DMOS output transistors monitor

and provide fast, independent protection control functions for

each individual output. All outputs have internal 45 V at 0.5 A

independent output voltage clamps to provide fast inductive

turn-off and transient protection.

The 33291L uses high-efficiency updrain power DMOS

output transistors exhibiting very low room temperature

drain-to-source ON resistance values (RDS(ON) ≤ 1.0 Ω at

13 V VPWR) and dense CMOS control logic. Operational bias

currents of less than 2.0 mA (1.0 mA typical) with any

combination of outputs ON are the result of using this mixed

technology and would not be possible with bipolar structures.

To accomplish a comparable functional feature set using a

bipolar structure approach would result in a device requiring

hundreds of milliamperes of internal bias and control current.

This would represent a very large amount of power to be

consumed by the device itself and not available for load use.

During operation, the 33291L functions as an eight 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 33291L directly

relieves the MCU of the fault management functions. The

33291L directly interfaces to an MCU, operating at system

clock serial frequencies in excess of 3.0 MHz. It uses a

Synchronous Peripheral Interface (SPI) for control and

diagnostic readout. Figure 12 illustrates the basic SPI

configuration between an MCU and one 33291L.

MC68HCXX

Microcontroller

Shift Register

MOSI

MISO

33291

SI

Shift Register

SO

Receive

Buffer

Parallel

Ports

SCLK

RST

CS

To

Logic

Figure 12. SPI Interface with Microcontroller

The circuit can also be used in a variety of other

applications in the computer, telecommunications, and

industrial fields. It is parametrically specified over an input

battery/supply range of 9.0 V to 16 V but is designed to

operate over a considerably wider range of 5.5 V to 26.5 V.

The design incorporates the use of logic level MOSFETs as

output devices. These MOSFETs are sufficiently turned ON

with a gate voltage of less than 5.0 V, thus eliminating the

need for an internal charge pump. Each output is identically

sized and independent in operation. The efficiency of each

output transistor is such that at room temperature with as little

as 9.0 V supply (VPWR), the maximum RDS(ON) of an output

at room temperature is 1.2 Ω (0.9 Ω typical) and increases to

only 2.0 Ω as VPWR is decreased to 5.5 V.

All inputs are compatible with 5.0 V CMOS logic levels,

incorporating negative or inverted logic. Whenever an input is

programmed to a logic low state (<1.0 V) the corresponding

low side switched output being controlled will be active low

and turned ON. Conversely, whenever an input is

programmed to a logic high state (>3.0 V), the output being

controlled will be high and turned OFF.

One main advantage of the 33291L is the serial port.

When coupled to an MCU, it receives ON/OFF commands

from the MCU and in return transmits the drain status of the

device’s output switches. Many devices can be daisy-

chained together, forming a larger system, as illustrated in

Figure 13, page 12.

Note In this example, only one dedicated MCU parallel

port (aside from the required SPI) is required for chip select

to control 32 possible loads.

Analog Integrated Circuit Device Data

Freescale Semiconductor

33291L

11

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