MC33390D/DR2 Ver la hoja de datos (PDF) - Motorola => Freescale

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Fabricante

MC33390D/DR2

Class B Serial Transceiver

Motorola => Freescale 

Freescale Semiconductor, Inc.

Table 1. Class B Bus Capacitance and Resistance Expressions

Level

Capacitance

Resistance to Ground

Minimum

(3.3 x 0.9) + (0.47 x 0.9) = 3.39 nF

(1.5 x 0.95) || (10.6 x 0.95) / 25 = 314 Ω

Maximum

(3.3 x 1.1) + 25(0.47 x 1.1) = 16.55 nF (1.5 x 1.05) || (10.6 x 1.05) = 1.38 kΩ

APPLICATIONS

Class B Module Inputs

Transmitter Data from the MCU (Tx)

The Tx input is a push-pull (N-channel/P-channel FETs)

buffer with hysteresis for noise immunity purposes. This pin is a

5.0 V CMOS logic level input from the MCU following a true

logic protocol. A logic [0] input drives the BUS output to 0 V (via

the external pull-down resistor to ground on each node), while

a logic [1] input produces a high voltage at the BUS output. A

logic [0] input level is guaranteed when the Tx input pin is open-

circuited by virtue of an internal 40 kΩ pull-down resistor. No

external resistor is required for its operation.

Waveshaping and 4X/Loop

This input is a tristateable input: 0 V = normal waveshaping,

5.0 V = waveshaping is disabled for 4X transmitting, and high

impedance = loopback mode of operation. This is a logic level

input used to select whether waveshaping for the Class B

output is enabled or disabled. A logic [0] enables waveshaping,

while a logic [1] disables waveshaping. In the 4X mode, the

BUS output rise time is less than 2.0 µs and the fall time is less

than 5.0 µs (owing to the external RC pull-down to ground). In

the loopback condition, the Tx signal is fed back to the Rx

output after waveshaping without being transmitted onto the

BUS. This mode of operation is useful for system diagnostic

purposes.

Class B Module Outputs

Transceiver Output (BUS)

This is the output driver stage that sources current to the bus.

Its output follows the waveshaped waveform input. Its output

voltage is limited to 6.25 V to 8.0 V under normal battery level

conditions. The limited level is controlled by an internal

regulator/clamp circuit. Once the battery voltage drops below

9.0 V, the regulator/clamp circuit saturates, causing the bus

voltage to track the battery voltage. A 1.5 kΩ ±5% external

resistor (as well as any 10.6 kΩ pull-down resistors of any

secondary nodes) sinks the current to discharge the capacitors

during high-to-low transitions. This sourcing output is short

circuit-protected (60 mA to 170 mA) against a short to -2.0 V

and sinks less than 1.0 mA when shorted to VBAT. If a short

occurs, the overtemperature shutdown circuit protects the

source driver of the device. In the event battery power is lost to

the assembly, the bus transmitter's output stage will be disabled

and the leakage current from the BUS output will not source or

sink more than 100 µA of current. The transceiver will operate

with a remote ground offset of ±2.0 V, but the lower corners of

transmission will not be rounded during this condition.

Receiver Output to the Microcontroller (Rx)

This is a 5.0 V CMOS compatible push-pull output used to

send received data to the microcontroller. It does not require an

external pull-up resistor to be used. The receiver is always

enabled and draws less than 65 µA of current from VBAT. The

receive threshold is dependent on the state of the SLEEP pin.

The receiver circuitry is able to operate with VBAT voltages as

low as 4.25 V and still remains capable of “waking up” the

33390 when remote Class B activity is detected.

When the SLEEP pin is 0 V and message activity occurs on

the bus, the receiver passes the bus message through to the

microcontroller. The 33390 does not automatically “wake up”

from a sleep state when bus activity occurs: the microcontroller

must tell it to do so.

In the Static Electrical Characteristics table, the maximum

voltage for Rx is specified as 4.75 V over an operating range of

-40°C to 125°C temperature and 7.0 V to 16 V VBAT. This

maximum Rx voltage is compatible with the minimum VDD

voltage of microcontrollers to prevent the 33390 from sourcing

current to the microcontroller's output.

Switched Ground Output (LOAD)

Normally this output is a saturated switch to ground, which

pulls down the external resistor between the BUS and LOAD

outputs. In the event ground is lost to the assembly, the LOAD

output will bias itself “off” and will not leak more than 100 µA of

current out of this pin.

Overtemperature Shutdown

If the BUS output becomes shorted to ground for any

duration, an overtemperature shutdown circuit “latches off” the

output source transistor whenever the die temperature exceeds

150°C to 190°C. The output transistor remains latched off until

the Tx input is toggled from a logic [0] to a logic [1]. The rising

edge provides the clearing function, provided the locally sensed

temperature is 10°C to 15°C below the latch-off temperature trip

temperature.

Waveshaping

Waveshaping is incorporated into the 33390 to minimize

radiated EMI emissions.

33390

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