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ELH0033G/883B

Fast Buffer Amplifier

Elantec -> Intersil 

ELH0033G 883 8001401ZX

Fast Buffer Amplifier

Applications Information

Recommended Layout Precautions

RF video printed circuit board layout rules

should be followed when using the ELH0033

since it will provide power gain to frequencies

over 100 MHz Ground planes are recommended

and power supplies should be decoupled at each

device with low inductance capacitors In addi-

tion ground plane shielding may be extended to

the metal case of the device since it is electrically

isolated from internal circuitry Alternatively

the case should be connected to the output to

minimize input capacitance

Offset Voltage Adjustment

The ELH0033’s offset voltages have been active-

ly trimmed by laser to meet guaranteed specifica-

tions when the offset preset pin is shorted to the

offset adjust pin The pre-calibration allows the

devices to be used in most DC or AC applications

without individually offset nulling each device If

offset null is desirable it is simply obtained by

leaving the offset preset pin open and connecting

a trim pot of 100X between the offset adjust pin

and Vb

Operation from Single or Asymmetrical

Power Supplies

This device type may be readily used in applica-

tions where symmetrical supplies are unavailable

or not desirable A typical application might be

an interface to a MOS shift register where Va e

a5V and Vb e b12V In this case an apparent

output offset occurs due to the device’s voltage

gain of less than unity This additional output

offset error may be predicted by

(V a bVb)

DVOj(1bAV)

e0 005 (VabVb)

2

where AV e No load voltage gain typically 0 99

Va e Positive supply voltage

Vb e Negative supply voltage

For the above example DVO would be b35 mV

This may be adjusted to zero as described in Sec-

tion 2 For AC coupled applications no addition-

al offset occurs if the DC input is properly biased

as illustrated in the ‘‘typical applications’’ sec-

tion

Short Circuit Protection

In order to optimize transient response and out-

put swing output current limit has been omitted

from the ELH0033 Short circuit protection may

be added by inserting appropriate value resistors

between Va and VCa pins and Vb and VCb

pins Resistor values may be predicted by

Va Vb

RLIM j ISC e ISC

where ISC s 100 mA for ELH0033

The inclusion of limiting resistors in the collec-

tors of the output transistors reduces output volt-

age swing Decoupling VCa and VCb pins with

capacitors to ground will retain full output swing

for transient pulses An alternate active current

limit technique that retains full DC output swing

uses current sources which are saturated during

normal operation thus applying full supply volt-

age to the VC pins Under fault conditions the

voltage decreases as required by the overload

RLIM

j

VBE

ISC

e

0

60

6V

mA

e

10X

Capacitive Loading

The ELH0033 is designed to drive capacitive

loads such as coaxial cables in excess of several

thousand picofarads without susceptibility to os-

cillation However peak current resulting from

(C c dv dt) should be limited below absolute

maximum peak current ratings for the devices

Thus

DVIN

Dt

c

CL

s

IOUT

s

g250

mA

In addition power dissipation resulting from

driving capacitive loads plus standby power

should be kept below the total package power

rating

PD pkg t PDC a PAC

PD pkg t (Va b Vb) c IS a PAC

PAC j (VP-P)2 c f c CL

6

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