MC33897ADSLASHR2 datasheet(14/20 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33897/A/B/C/D/T

FUNCTIONAL DESCRIPTION

FUNCTIONAL BLOCK DIAGRAM COMPONENTS

diode is generally used to protect the entire module from

reverse battery and should be selected accordingly.

BUS I/O

This input/output may require electrostatic discharge

(ESD) and/or EMI external circuitry. A set of components is

shown in the simplified application diagrams on page 16 of

this datasheet. The value of the capacitor should be adjusted

downward in direct proportion to the added capacitance of

the ESD or EMI circuits. The series resistance of the inductor

should be kept below 3.5

Ω to prevent its voltage drop from

significantly degrading system noise margins.

FUNCTIONAL BLOCK DIAGRAM COMPONENTS

Timer OSC

This circuit generates a 500 kHz signal to be used for

internal logic. It is the reference for some of the required

delays.

Timers

This circuit contains the timing logic used to hold the CNTL

active for the required time after the conditions for sleep

mode have been met. It is also used to keep the TXD driver

active for a period of time after it has generated a passive

level on the bus.

Mode Control

This circuit contains the control logic for the various

operating modes and conditions required for the IC.

BUS RCVR

This circuit translates the levels on the BUS terminal to a

CMOS level indicating the presence of a logic [0] or a

logic [1]. It also determines the presence of a high-voltage

wake-up (HVWU) signal that is passed to Mode Control and

Timers circuits. An analog filter is used to “de-glitch” the high-

voltage wake-up signal and prevent false exits from the sleep

mode.

TXD BUS DRVR

This circuit drives the BUS. It can drive it with the higher

voltage wake-up signals when enabled by the Mode Control

circuit. It can also provide waveshaping for reduced EMI or

not provide it for the higher data rate mode. The actual data

is received on TXD at CMOS logic levels, then translated by

this circuit to the necessary operating voltages.

Undervoltage Detect

This circuit monitors internal operating voltage to assure

proper operation of the part. If a low-voltage condition is

detected, it sends a signal to disable the BUS RCVR and

TXD BUS DRVR circuits. This prevents incorrect data from

being put on the bus or sent to the MCU.

Load Switch

The LOAD switch provides a path for an external resistor

connected to the BUS to be connected to ground. When a

loss of ground is detected, this switch is opened to prevent

the current that would normally be flowing to the ground from

the module from going back through the load resistor and

raising the bus level. The circuit is opened when the voltage

between GND and VBATT becomes too low as would be the

case if module ground were lost.

MC33897AD/R2 Datasheet(PDF) 14 Page - Freescale Semiconductor, Inc

MC33897AD/R2 Datasheet(HTML) 14 Page - Freescale Semiconductor, Inc

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