33990

MOTOROLA ANALOG INTEGRATED CIRCUIT DEVICE DATA

10

SYSTEM/APPLICATION INFORMATION

INTRODUCTION

The 33990 is a serial transceiver device designed to meet

the SAE Standard J-1850 Class B performance for bi-

directional half-duplex communication. The device is packaged

in an economical surface-mount SOIC plastic package. An

internal block diagram of the device is shown in Figure 1.

The 33990 derives its robustness to temperature and voltage

extremes from being built on a SMARTMOS process,

incorporating CMOS logic, bipolar/MOS analog circuitry, and

DMOS power FETs. Though the 33990 was principally

designed for automotive applications requiring SAE J-1850

Class B standards, it is suited for other serial communication

applications. It is parametrically specified over an ambient

temperature range of -40

16 V supply. The economical 8-pin SOICN surface mount

plastic package makes the device a cost-effective solution.

FUNCTIONAL DESCRIPTION

This is the only required input power source necessary to

operate the 33990. The internal voltage reference of the 33990

will remain fully operational with a minimum of 9.0 V on this pin.

Bus transmissions can continue with battery voltages down to

5.0 V. The bus output voltage will follow the battery voltage

down and, in doing so, track approximately 1.6 V below the

battery voltage. The device will continue to receive and transmit

bus data to the microcontroller with battery voltages as low as

4.25 V. The pin can withstand voltages from -16 V to 40 V.

This input is used to enable and disable the Class B

transmitter. The Class B receiver is always enabled so long as

voltage is 5.0 V, the Class B transmitter is enabled. If this input

is 0 V, the Class B transmitter will be disabled and less than

provides a 5.0 V reference, internal to the device, used to

establish the Rx output level and slew rate times.

Class B Functional Description

The transmitter provides an analog waveshaped 0 V to 7.0 V

waveform on the BUS output. It also receives waveforms and

transmits a digital level signal back to a logic IC. The transmitter

can drive up to 32 secondary Class B transceivers (see

Figures 9 and 10). These secondary nodes may be at ground

potentials that are

±2.0 V relative to the control assembly.

Waveshaping will only be maintained during 2 of the 4 corners

when the 0 to

±2.0 V ground potential difference condition

exists. The 33990 is a secondary node on the Class B bus.

Each secondary transceiver has a 470

±10% pF capacitor on

its output for EMI suppression purposes, as well as a 10.6 k

Ω

±5% pull-down resistor to ground. The primary node has a

3300

±10% pF capacitor on its output for EMI suppression, as

well as a 1.5 k

Ω ±5% pull-down resistor to ground. With more

than 26 nodes, there is no primary node (see Figure 11). All

nodes will have a 470

±10% pF capacitor and a 10.6 kΩ ±5%

pull-down resistor. No matter how many secondary nodes are

on the Class B bus, the RC time constant of the Class B bus is

maintained at approximately 5.0 µs. The minimum and

maximum capacitance and resistance on the Class B bus is

given by the expressions shown in Table 1.

Figure 9. Minimum Bus Load

Figure 10. Maximum Number of Nodes

Figure 11. Maximum Bus Load

3300 pF

1.5 k

Ω

470 pF

10.6 k

Ω

One Primary Node

1.5 k

Ω

470 pF

10.6 k

Ω

Primary Node

442

Ω

24 Secondary Nodes

3300 pF

11280 pF

14570 pF

342

Ω

470 pF

10.6 k

Ω

31 Secondary Nodes

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com