L6238 datasheet(3/35 Pages) STMICROELECTRONICS

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GENERAL DESCRIPTION

The L6238 is an integrated circuit that will be

used to commutate and speed control a 3-Phase,

8-pole, brushless, DC motor. The primary applica-

tion is for disk drive spindle motors. This I.C. has

the following features:

No Motor Hall Effect Sensors are required for

commutation or speed control. Timing informa-

tion is determined from the Bemf voltage of the

undriven motor terminal.

On-board Speed Control via a Phase Locked

Loop that accepts a once-per-rev reference

frequency and locks the motor to that fre-

quency. The L6238 can accomodate a wide

range of speeds.

The L6238 achieves Spindle Synchronization

by locking to a once-per-rev reference that is

common to multiple drives. The L6238 has a

multiplexer that enhances the versatility of the

controller. This first multiplexer selects either

internal feedback, (generated by the Bemf of

the motor), or external feedback (embedded

index).

An External P-Channel FET can be connected

to the FET can be connected to the FET

Bridge for Higher Power Applications.

In this configuration, the internal DMOS drivers

are sequenced in full conduction state and the

external PFET is the linear control element. An

internal inverting buffer from the output of the

OTA controls the conduction of the EXT PFET.

An internal Virtual Center Tap is used if the

motor center tap is not connected.

The motor Current Limit can be set by an ex-

ternal resistor divider.

A Serial Port is included so that I/O can be

done with a minimum of pins. Key control and

status lines are also bonded out to achieve a

Minimum Configuration without using the Serial

Port.

Programmable

Functions

include

Phase

Switch Timing Optimization for motor effi-

ciency, Speed Lock Threshold, Auto-Start or

mP Supervised Spinup, and output current lim-

iting gain.

Energy Recovery Mode for Head Retraction,

followed by Dynamic Braking Mode.

Logic signals are CMOS Compatible.

Stuck Rotor and Backward Rotation detection.

Automatic Thermal Shutdown with early warn-

ing bit available in the status register

PIN FUNCTIONS

Name

I/O

Function

OUTPUT B

I/O

DMOS Half Bridge Output and Input B for Bemf sensing.

SPIN SENSE

Toggless at each Zero Crossing of the Bemf.

BRAKE DELAY

Energy Recovery time constant, defined by external R-C to ground.

4Rsense

Outputs A+B connections for the Motor Current Sense Resistor to ground

CHARGE PUMP 2

Negative Terminal of Pump Capacitor.

6, 7,

17, 29,

39, 40

GROUND

Ground terminals.

CHARGE PUMP 1

Positive terminal of Pump Capacitor.

CHARGE PUMP 3

Positive terminal of Storage Capacitor.

OUTPUT A

I/O

DMOS Half Bridge Output and Input A for Bemf sensing.

11, 42

Vpower

Supplies the voltage for the Power Section.

Vanalog

12V supply.

SER PORT

DISABLE

Input for tri-stating the serial port.

SER DATA R/W

Selects Serial Data Read or Write Function.

SER STROBE

Dtat Strobe Input.

SER PORT CLK

Clock for Serial Data Control.

SER DATA I/O

I/O

Data stream Input/Output for Control/Status Registers.

EXT/INT

Selects thr Internal BEMF Zero Crossing or an External Source as Feedback

Frequency for te PLL.

FREF ENABLE

A zero on this pin passes the PLL Fref signal to the Freq/phase detector.

LINEAR

This input should be grounded or left unconnected.

OUTPUT

ENABLE

Tristates Power Output Stage when a logic zero.

L6238

3/35

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