EL1056C 데이터 시트보기 (PDF) - Elantec -> Intersil

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EL1056C

Monolithic High-Speed Pin Driver

Elantec -> Intersil 

EL1056AC EL1056C

Monolithic High-Speed Pin Driver

Applications Information Contd

Overcurrent Protection

The sense comparators are available to alert the

test system’s controller that the driver is output-

ting excessive current Shunt resistors are con-

nected from Ba to Shunta and Bb to Shuntb

When the internal comparators sense more than

a nominal 200 mV drop on the shunts they cause

a 1 5 mA current to be sunk from the Sense ter-

minal The comparators are of ‘‘slow attack fast

decay’’ design so that transient load currents will

not trigger a sense output only a sustained over-

current will

The sense resistors must not be inductive and

the skin resistance of long narrow connections

between Shunt and Ba or Bb can cause tran-

sient voltages that produce output overshoot

(but not ringing)

The Sense output is simply a switched current

source connected to Vb It can be used to inter-

face to CMOS TTL or ECL inputs For CMOS

and TTL it can be connected to a pull-up resistor

to a5V of 10K value This establishes a logic

high value and a clamp diode (internal to TTL)

establishes a low level of b0 6V For ECL a gate

should be available to provide a static logic high

level An 820X pull-up resistor is wired to that

output The logic low will be more negative than

is usual for ECL but this will cause no problem

In all cases multiple Sense outputs may be con-

nected together from many drivers to effect a

wired-or function

A further protection scheme is to provide a series

resistor from Ba to Va and Bb to Vb The

resistor serves to limit the output fault current

by allowing Ba and Bb voltages to sag under

heavy load This also reduces the dissipation on

the output transistors for valid loads Because

Ba and Bb are separately bypassed these volt-

ages will sustain under transient loads and dy-

namics will not be affected

Output Accuracy

The accuracy of the output voltage depends on

several factors The first is the gain error from

VINH or VINL to the output unloaded The gain

error is nominally b0 6% and has a few tenths

of a percent variation between parts The second

is supply rejection If the Ba Bb Shunta or

Shuntb voltages are different from those used

by Elantec to test the part there will be about

2 2 mV systematic shift in output offset per volt

of supply variation The Va and Vb supplies

have much less influence on output error Final-

ly there is a random VOS error as specified in the

data table

Of course the finite output impedance of the

EL1056 will cause additional output error when

the driver is loaded

Power-Down

The EL1056 incorporates a power-down feature

that drastically reduces power consumption of an

unused driver and also drops the output leakage

current to nanoamperes (‘‘A’’ grade only) The

output is not a low capacitance in this mode

however and transients driven from the cable

can momentarily turn on the output transistors

Power-down is intended to allow the switching of

accurate DC meters onto the bus without having

to relay out the driver’s leakage current It takes

about 40 ms for the output leakage to sag to na-

noamperes but this is still much faster than re-

lays or voltmeters

Power-down is controlled by the E and E differ-

ential inputs There is no problem with logic am-

plitude or slewrate and input resistor networks

are not needed

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