34921 datasheet(18/36 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

34921

FUNCTIONAL DESCRIPTION

INTRODUCTION

FUNCTIONAL DESCRIPTION

INTRODUCTION

The serial interface of the MC34921 is a three input, one

output interface similar to a Serial Peripheral Interface (SPI)

port in general form, but different in specific clocking

requirements due to the fact that an A/D converter cannot

reliably run without a continuous clock. The 34921 serial

interface communicates to a microcontroller unit (MCU) at up

to 16 MHz. The serial signals are SCLK, CE, MOSI, and

MISO. The SCLK signal pin requires a free-running clock (up

to 16 MHz) which is provided by the MCU. This signal is

required to ensure proper operation of both the ADC and the

reset timer circuitry. The serial data transfers between the

MCU and the 34921 via the MOSI and MISO terminals. The

serial data from the MCU is handled in the MC34921 via two

input registers -- the NORMAL input register contains bits

controlling the motor drivers as well as the A/D converter, and

the CONFIG register contains bits relating to the general

configuration setup of the device. The MC34921 also has two

output registers -- the NORMAL output register reports A/D

conversion data as well as digital encoder data, and the IREQ

output register reports under voltage, temperature, and other

device status data.

FUNCTIONAL TERMINAL DESCRIPTION

GROUND (GND)

Main ground. It is used for the B+ filters and motor filter

grounds, as well as the ground return for external

components which are used with the linear and switching

regulators.

COVER VOLTAGE OUTPUT SELECT (VCORE

SELECT)

This terminal is used to select the output voltage provided

by the VCORE linear regulator. The VCORE Select potential

is latched in during the MC34921's power-on sequence. The

MC34921 will not respond to changes in VCORE Select after

power up.

UNIPOLAR STEP A/DC MOTOR C OUTPUT A (SA/

CDCMA)

A low-side driver output is configurable for either stepper

motor control (SA) or C DC motor (as CDCMA, which

requires an external hardwire to pin 63) via the serial I/O. The

driver is PWM controlled via the CPWMA/CDCPWM pin, and

direction controlled via the Serial I/O. It includes an active

voltage clamp, current limit, and thermal shutdown

protection.

UNIPOLAR STEP A/DC MOTOR C OUTPUT B (SA/

CDCMB)

A low-side driver output is configurable for either stepper

motor control (SA) or C DC motor (as CDCMB, it requires

external hardwire to pin 61) via the serial I/O. The driver is

PWM controlled via the CPWMA/CDCPWM pin, and

direction controlled via the Serial I/O. It includes active

voltage clamp, current limit, and thermal shutdown

protection.

UNIPOLAR STEP B/LOW-SIDE 1 (SB/LSOUT1)

A low-side driver output is configurable for either stepper

motor control (SB) or as a general purpose low-side driver

(LSOUT1) via the serial I/O. The SB is PWM controlled via

the CPWMB pin. The direction and LSOUT1 are controlled

via the serial I/O. It includes active voltage clamp, current

limit and thermal shutdown protection.

UNIPOLAR STEP B/LOW-SIDE 2 (SB/LSOUT2)

A low-side driver output is configurable for either stepper

motor control (SB) or as a general purpose low-side driver

(LSOUT2) via the serial I/O. The SB is PWM controlled via

the CPWMB pin. The direction and LSOUT2 are controlled

via the serial I/O. It includes active voltage clamp, current

limit and thermal shutdown protection.

POWER SUPPLY INPUT (B+)

This is the main power supply input for the regulators and

DC motor drivers.

3.3 V SWITCHING REGULATOR SWITCH OUTPUT

(3.3 V SWITCH)

The high-side driver output is used for the 3.3v switching

regulator. It uses the internal 200KHZ clock.

3.3 V REGULATOR FEEDBACK (3.3 V)

This terminal is the error amp feedback for the 3.3v

switching regulator. It is also the output point for the 3.3v

switching supply.

CORE VOLTAGE REGULATOR INPUT (VCORE

SUPPLY)

The input voltage terminal for the VCORE linear supply,

which is usually provided by externally hardwiring the 3.3v

switching regulator output.

CORE VOLTAGE REGULATOR OUTPUT (VCORE)

The output terminal of the VCORE linear regulator.

Voltage options of 1.5v, 1.8v, or 2.5v are set by the potential

of the VCORE Select pin at power up. It features current limit

34921 Datasheet(PDF) 18 Page - Freescale Semiconductor, Inc

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