The L98SIDMOS outputis a lowoperatingpowerde-

vice featu-ring, eight 1

transient protection circuits in output stages. Each

channel is independently controlled by an output

latch and a common RESET line which disables all

eightoutputs.The driver has low saturationandshort

circuitprotectionandcan driveinductiveandresistive

loads such as solenoids, lamps and relais. Data is

transmitted to the device serially using the Serial Pe-

ripheral Interface (SPI) protocol. The circuit receives

8 bitserial databy meansof the serial input(SI) which

is stored in an internal register to control the output

drivers. The serial output (SO) provides 8 bit of dia-

gnostic data representingthe voltagelevel at the dri-

ver output. This allows the microprocessor to

diagnose the condition of the output drivers.

The output saturation voltage is monitored by a

comparator for an out of saturation condition and is

able to unlatch the particular driver through the fault

reset line. This circuit is also cascadable with ano-

ther octal driver in order to jam 8 bit multiple data.

The device is selected when the chip enable (CE)

line is low.

Additionally the (SO) is placed in a tri-state mode

when the device is deselected. The negative edge

of the (CE) transfers the voltage level of the drivers

to the shift register and the positive edge of the (CE)

latchesthe new datafrom the shift register to the dri-

vers. When CE is Low, data bit contained into the

shift register is transferred to SO output at every

SCLK positive transition while data bit present at SI

input is latched into the shift register on every SCLK

negative transition.

Internal Blocks Description

The internal architecture of the device is based on

the three internal major blocks : the octal shift regi-

ster for talking to the SPI bus, the octal latch for hol-

ding control bits written into the device and the octal

load driver array.

Shift Register

The shift register has both serial and parallel inputs

and serial and parallel outputs. The serial input ac-

cepts data from the SPI bus and the serial output si-

multaneously sends data into the SPI bus. The

parallel outputs are latched into the parallel latch in-

side the L98SI at the end of a data transfer. The pa-

rallel inputsjam diagnosticdatainto the shift register

at the beginning of a data transfer cycle.

Parallel Latch

The parallel latch holds the input data from the shift

register. This data then actuates the output stages.

Individual registers in the latch may be cleared by

fault conditions in order to protect the overloaded

output stages. The entire latch may also be cleared

by the RESET signal.

Output Stages

The output stagesprovide an active low drive signal

suitable for 0.75A continuous loads. Each output

has a current limit circuit which limits the maximum

output current to at least 1.05A to allow for high in-

rush currents. Additionally,the outputshaveinternal

zeners set to 36 volts to clamp inductive transients

at turn-off. Each output also has a voltage compa-

rator observing the outputnode. If the voltage exce-

eds 1.8V on an ON output pin, a fault condition is

assumed and the latch driving this particular stage

is reset, turning the output OFF to protect it. The ti-

ming of this action is described below. These com-

parators also provide diagnostic feedback data to

the shift register. Additionally, the comparators con-

tain an internalpulldowncurrentwhich will causethe

cell to indicate a low output voltage if the output is

programmed OFF and the output pin is open circui-

ted.

TIMING DATA TRANSFER

Figure #2 shows the overall timing diagram from a

byte transfer to and from the L98SI using the SPI

bus.

CE High to Low Transition

The action begins when the Chip Enable(CE) pin is

pulledlow. The tri-state Serial Output(SO) pin driver

will be enabledentire time that CE is low. At the fal-

ling edge of the CE pin, the diagnostic data from the

voltage comparators in the output stages will be lat-

ched into the shift register. If a particular output is

high, a logic one will be jammed into that bit in the

shift register. If the output is low, a logic zero will be

loaded there. The most significant bit (07) shouldbe

presented at the Serial Input (SI) pin. A zero at this

pin will program an output ON, while a one will pro-

gram the output OFF.

SCLK Transitions

The Serial Clock (SCLK) pin should then be pulled

high. At thispoint the diagnostic bit from the most si-

gnificantoutput(07) will appearat the SO pin. A high

here indicates that the 07 pin is higher than 1.8V.

The SCLK pin shouldthen be toggledlow then high.

New SO data will appearfollowing every rising edge

of SCLK and new SI data will be latched into the

L98SIshift registeron the fallingedges.An unlimited

amount of data may be shifted through the device

FUNCTIONAL DESCRIPTION

L98SI

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