National Semiconductor LM628, LM629 Technical data

LM628/LM629 Precision Motion Controller

January 2003

General Description

The LM628/LM629 are dedicated motion-control processors designed for use with a variety of DC and brushless DC servo motors, and other servomechanisms which provide a quadrature incremental position feedback signal. The parts perform the intensive, real-time computational tasks required for high performance digital motion control. The host control software interface is facilitated by a high-level command set. The LM628 has an 8-bit output which can drive either an 8-bit or a 12-bit DAC. The components required to build a servo system are reduced to the DC motor/actuator, an incremental encoder, a DAC, a power amplifier, and the LM628. An LM629-based system is similar, except that it provides an 8-bit PWM output for directly driving H-switches. The parts are fabricated in NMOS and packaged in a 28-pin dual in-line package or a 24-pin surface mount package (LM629 only). Both 6 MHz and 8 MHz maximum frequency versions are available with the suffixes -6 and -8, respectively, used to designate the versions. They incorporate an SDA core processor and cells designed by SDA.

Features

n 32-bit position, velocity, and acceleration registers n Programmable digital PID filter with 16-bit coefficients n Programmable derivative sampling interval n 8- or 12-bit DAC output data (LM628) n 8-bit sign-magnitude PWM output data (LM629) n Internal trapezoidal velocity profile generator n Velocity, target position, and filter parameters may be

changed during motion

n Position and velocity modes of operation n Real-time programmable host interrupts n 8-bit parallel asynchronous host interface n Quadrature incremental encoder interface with index

pulse input

n Available in a 28-pin dual in-line package or a 24-pin

surface mount package (LM629 only)

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FIGURE 1. Block Diagram

TRISTATE&®is a registered trademark of National Semiconductor Corporation.

Connection Diagrams

LM628N LM629N LM629M

LM628/LM629

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*Do not connect.

Order Number LM629M-6, LM629M-8, LM628N-6, LM628N-8, LM629N-6 or LM629N-8

See NS Package Number M24B or N28B

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LM628/LM629

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

Voltage at Any Pin with

≤ 85˚C, (Note 2) 605 mW

ESD Tolerance

= 120 pF, R

ZAP

= 1.5k) 1000V

ZAP

Operating Ratings

Respect to GND −0.3V to +7.0V

Ambient Storage Temperature −65˚C to +150˚C

Lead Temperature

28-pin Dual In-Line

Package (Soldering, 4 sec.) 260˚C

24-pin Surface Mount

Package (Soldering, 10 sec.) 300˚C

Maximum Power Dissipation

Temperature Range −40˚C<T

Clock Frequency:

LM628N-6, LM629N-6,

LM629M-6 1.0 MHz

LM628N-8, LM629N-8,

LM629M-8 1.0 MHz

Range 4.5V<V

CLK

DC Electrical Characteristics

(VDDand TAper Operating Ratings; f

Symbol Parameter Conditions Tested Limits Units

Supply Current Outputs Open 110 mA

INPUT VOLTAGES

Logic 1 Input Voltage 2.0 V

Logic 0 Input Voltage 0.8 V

Input Currents 0 ≤ VIN≤ V

OUTPUT VOLTAGES

OUT

Logic 1 IOH= −1.6 mA 2.4 V

Logic 0 IOL= 1.6 mA 0.4 V

TRI-STATE®Output Leakage Current 0 ≤ V

CLK

= 6 MHz)

OUT

≤ V

Min Max

−10 10 µA

+85˚C

6.0 MHz

8.0 MHz

5.5V

AC Electrical Characteristics

(VDDand TAper Operating Ratings; f

Timing Interval T

ENCODER AND INDEX TIMING (See Figure 2)

Motor-Phase Pulse Width T1

Dwell-Time per State T2

Index Pulse Setup and Hold T3 0 µs

(Relative to A and B Low)

CLOCK AND RESET TIMING (See Figure 3)

Clock Pulse Width

LM628N-6, LM629N-6, LM629M-6 T4 78 ns

LM628N-8, LM629N-8, LM629M-8 T4 57 ns

Clock Period

LM628N-6, LM629N-6, LM629M-6 T5 166 ns

LM628N-8, LM629N-8, LM629M-8 T5 125 ns

Reset Pulse Width T6

= 6 MHz; C

CLK

= 50 pF; Input Test Signal tr=tf= 10 ns)

LOAD

Tested Limits Units

Min Max

µs

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AC Electrical Characteristics (Continued)

(VDDand TAper Operating Ratings; f

Timing Interval T

LM628/LM629

STATUS BYTE READ TIMING (See Figure 4)

Chip-Select Setup/Hold Time T7 0 ns

Port-Select Setup Time T8 30 ns

Port-Select Hold Time T9 30 ns

Read Data Access Time T10 180 ns

Read Data Hold Time T11 0 ns

RD High to Hi-Z Time

COMMAND BYTE WRITE TIMING (See Figure 5)

Chip-Select Setup/Hold Time T7 0 ns

Port-Select Setup Time T8 30 ns

Port-Select Hold Time T9 30 ns

Busy Bit Delay T13 (Note 3) ns

WR Pulse Width

Write Data Setup Time T15 50 ns

Write Data Hold Time T16 120 ns

DATA WORD READ TIMING (See Figure 6)

Chip-Select Setup/Hold Time T7 0 ns

Port-Select Setup Time T8 30 ns

Port-Select Hold Time T9 30 ns

Read Data Access Time T10 180 ns

Read Data Hold Time T11 0 ns

RD High to Hi-Z Time

Busy Bit Delay T13 (Note 3) ns

Read Recovery Time T17 120 ns

DATA WORD WRITE TIMING (See Figure 7)

Chip-Select Setup/Hold Time T7 0 ns

Port-Select Setup Time T8 30 ns

Port-Select Hold Time T9 30 ns

Busy Bit Delay T13 (Note 3) ns

WR Pulse Width

Write Data Setup Time T15 50 ns

Write Data Hold Time T16 120 ns

Write Recovery Time T18 120 ns

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating the device beyond the above Operating Ratings.

Note 2: When operating at ambient temperatures above 70˚C, the device must be protected against excessive junction temperatures. Mounting the package on a printed circuit board having an area greater than three square inches and surrounding the leads and body with wide copper traces and large, uninterrupted areas of copper, such as a ground plane, suffices. The 28-pin DIP (N) and the 24-pin surface mount package (M) are molded plastic packages with solid copper lead frames. Most of the heat generated at the die flows from the die, through the copper lead frame, and into copper traces on the printed circuit board.The copper traces act as a heat sink. Double-sided or multi-layer boards provide heat transfer characteristics superior to those of single-sided boards.

Note 3: In order to read the busy bit, the status byte must first be read. The time required to read the busy bit far exceeds the time the chip requires to set the busy bit. It is, therefore, impossible to test actual busy bit delay. The busy bit is guaranteed to be valid as soon as the user is able to read it.

= 6 MHz; C

CLK

= 50 pF; Input Test Signal tr=tf= 10 ns)

LOAD

Tested Limits Units

Min Max

T12 180 ns

T14 100 ns

T12 180 ns

T14 100 ns

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FIGURE 2. Quadrature Encoder Input Timing

LM628/LM629

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FIGURE 3. Clock and Reset Timing

FIGURE 4. Status Byte Read Timing

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LM628/LM629

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FIGURE 5. Command Byte Write Timing

FIGURE 6. Data Word Read Timing

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Pinout Description

(See Connection Diagrams) Pin numbers for the 24-pin surface mount package are indicated in parentheses.

Pin 1 (17), Index (IN) Input: Receives optional index pulse from the encoder. Must be tied high if not used. The index position is read when Pins 1, 2, and 3 are low.

Pins 2 and 3 (18 and 19), Encoder Signal (A, B) Inputs:

Receive the two-phase quadrature signals provided by the incremental encoder. When the motor is rotating in the positive (“forward”) direction, the signal at Pin 2 leads the signal at Pin 3 by 90 degrees. Note that the signals at Pins 2 and 3 must remain at each encoder state (See Figure 9) for a minimum of 8 clock periods in order to be recognized. Because of a four-to-one resolution advantage gained by the method of decoding the quadrature encoder signals, this corresponds to a maximum encoder-state capture rate of 1.0 MHz (f

= 8.0 MHz) or 750 kHz (f

CLK

other clock frequencies the encoder signals must also remain at each state a minimum of 8 clock periods.

Pins 4 to 11 (20 to 24 and 2 to 4), Host I/O Port (D0 to D7):

Bi-directional data port which connects to host computer/ processor. Used for writing commands and data to the LM628, and for reading the status byte and data from the LM628, as controlled by CS (Pin 12), PS (Pin 16), RD (Pin

13), and WR (Pin 15).

= 6.0 MHz). For

CLK

Pinout Description (Continued)

within 1.5 ms. If the status word has not changed from hex “00” to “84” or “C4” within 1.5 ms, perform another reset and repeat the above steps. To be certain that the reset was

LM628/LM629

properly performed, execute a RSTI command. If the chip

FIGURE 8. 12-Bit Multiplexed Output Timing

has reset properly, the status byte will change from hex “84” or “C4” to hex “80” or “C0”. If this does not occur, perform another reset and repeat the above steps.

Pin 28 (16), Supply Voltage (V

): Power supply voltage

(+5V).

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Theory of Operation

INTRODUCTION

The typical system block diagram (See Figure 1) illustrates a servo system built using the LM628. The host processor communicates with the LM628 through an I/O port to facilitate programming a trapezoidal velocity profile and a digital compensation filter. The DAC output interfaces to an external digital-to-analog converter to produce the signal that is power amplified and applied to the motor. An incremental encoder provides feedback for closing the position servo loop. The trapezoidal velocity profile generator calculates the required trajectory for either position or velocity mode of operation. In operation, the LM628 subtracts the actual position (feedback position) from the desired position (profile generator position), and the resulting position error is processed by the digital filter to drive the motor to the desired position. Table 1 provides a brief summary of specifications offered by the LM628/LM629:

keep track of the absolute position of the motor. Each time a logic transition occurs at one of the quadrature inputs, the LM628 internal position register is incremented or decremented accordingly. This provides four times the resolution over the number of lines provided by the encoder. See Figure 9. Each of the encoder signal inputs is synchronized with the LM628 clock.

The optional index pulse output provided by some encoders assumes the logic-low state once per revolution. If the LM628 is so programmed by the user, it will record the absolute motor position in a dedicated register (the index register) at the time when all three encoder inputs are logic low.

If the encoder does not provide an index output, the LM628 index input can also be used to record the home position of the motor. In this case, typically, the motor will close a switch which is arranged to cause a logic-low level at the index input, and the LM628 will record motor position in the index register and alert (interrupt) the host processor. Permanently grounding the index input will cause the LM628 to malfunc-

POSITION FEEDBACK INTERFACE

tion.

The LM628 interfaces to a motor via an incremental encoder. Three inputs are provided: two quadrature signal inputs, and an index pulse input. The quadrature signals are used to

TABLE 1. System Specifications Summary

Position Range −1,073,741,824 to 1,073,741,823 counts

Velocity Range 0 to 1,073,741,823/2

counts/sample; ie, 0 to 16,383 counts/sample, with a resolution of 1/2

counts/sample

Acceleration Range 0 to 1,073,741,823/2

resolution of 1/2

counts/sample/sample; ie, 0 to 16,383 counts/sample/sample, with a

counts/sample/sample

Motor Drive Output LM628: 8-bit parallel output to DAC, or 12-bit multiplexed output to DAC

LM629: 8-bit PWM sign/magnitude signals

Operating Modes Position and Velocity

Feedback Device Incremental Encoder (quadrature signals; support for index pulse)

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