OPA682 datasheet(21/22 Pages) TI1

21 / 22 page

OPA2680

OPA2680 is nominally compensated to operate with a 2pF

parasitic load. Higher parasitic capacitive loads without an

RS are allowed as the signal gain increases (increasing the

unloaded phase margin) If a long trace is required, and the

6dB signal loss intrinsic to a doubly terminated transmission

line is acceptable, implement a matched impedance trans-

mission line using microstrip or stripline techniques (consult

an ECL design handbook for microstrip and stripline layout

techniques). A 50

Ω environment is normally not necessary

on board, and in fact, a higher impedance environment will

improve distortion as shown in the distortion versus load

plots. With a characteristic board trace impedance defined

(based on board material and trace dimensions), a matching

series resistor into the trace from the output of the OPA2680

is used as well as a terminating shunt resistor at the input of

the destination device. Remember also that the terminating

impedance will be the parallel combination of the shunt

resistor and the input impedance of the destination device;

this total effective impedance should be set to match the

trace impedance. The high output voltage and current capa-

bility of the OPA2680 allows multiple destination devices to

be handled as separate transmission lines, each with their

own series and shunt terminations. If the 6dB attenuation of

a doubly terminated transmission line is unacceptable, a

long trace can be series-terminated at the source end only.

Treat the trace as a capacitive load in this case and set the

series resistor value as shown in the plot of Recommended

RS vs Capacitive Load. This will not preserve signal integ-

rity as well as a doubly terminated line. If the input imped-

ance of the destination device is low, there will be some

signal attenuation due to the voltage divider formed by the

series output into the terminating impedance.

e) Socketing a high speed part like the OPA2680 is not

recommended. The additional lead length and pin-to-pin

capacitance introduced by the socket can create an ex-

tremely troublesome parasitic network which can make it

almost impossible to achieve a smooth, stable frequency

response. Best results are obtained by soldering the OPA2680

onto the board.

FIGURE 16. Internal ESD Protection.

External

–V

Internal

Circuitry

INPUT AND ESD PROTECTION

The OPA2680 is built using a very high speed complemen-

tary bipolar process. The internal junction breakdown volt-

ages are relatively low for these very small geometry de-

vices. These breakdowns are reflected in the Absolute Maxi-

mum Ratings table. All device pins are protected with

internal ESD protection diodes to the power supplies as

shown in Figure 16.

These diodes provide moderate protection to input overdrive

voltages above the supplies as well. The protection diodes

can typically support 30mA continuous current. Where higher

currents are possible (e.g., in systems with

±15V supply

parts driving into the OPA2680), current-limiting series

resistors should be added into the two inputs. Keep these

resistor values as low as possible since high values degrade

both noise performance and frequency response.

OPA682 Datasheet(PDF) 21 Page - Texas Instruments

OPA682 Datasheet(HTML) 21 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Datasheet Download

Link URL