LT1206

11

1206fa

APPLICATIONS INFORMATION

When the LT1206 is used to drive capacitive loads, the

available output current can limit the overall slew rate. In the

fastest configuration, the LT1206 is capable of a slew rate

of over 1V/ns. The current required to slew a capacitor at

this rate is 1mA per picofarad of capacitance, so 10,000pF

would require 10A! The photo (Figure 6) shows the large

60V/µs, determined by the current limit of 600mA.

the maximum allowable input voltage. To allow for some

margin, it is recommended that the input signal be less

than ±5V when the device is shut down.

Capacitance on the Inverting Input

Current feedback amplifiers require resistive feedback from

the output to the inverting input for stable operation. Take

care to minimize the stray capacitance between the output

and the inverting input. Capacitance on the inverting input

to ground will cause peaking in the frequency response

(and overshoot in the transient response), but it does not

degrade the stability of the amplifier.

Power Supplies

The LT1206 will operate from single or split supplies from

± 5V (10V total) to ±15V (30V total). It is not necessary to

use equal value split supplies, however the offset voltage

and inverting input bias current will change. The offset

voltage changes about 500µV per volt of supply mismatch.

The inverting bias current can change as much as 5µA

per volt of supply mismatch, though typically the change

is less than 0.5µA per volt.

Thermal Considerations

The LT1206 contains a thermal shutdown feature which

protects against excessive internal (junction) temperature.

If the junction temperature of the device exceeds the pro-

tection threshold, the device will begin cycling between

normal operation and an off state. The cycling is not

harmful to the part. The thermal cycling occurs at a slow

rate, typically 10ms to several seconds, which depends

on the power dissipation and the thermal time constants

of the package and heat sinking. Raising the ambient

temperature until the device begins thermal shutdown

gives a good indication of how much margin there is in

the thermal design.

For surface mount devices heat sinking is accomplished

by using the heat spreading capabilities of the PC board

and its copper traces. Experiments have shown that the

heat spreading copper layer does not need to be electri-

cally connected to the tab of the device. The PCB material

can be very effective at transmitting heat between the pad

area attached to the tab of the device, and a ground or

20ns/DIV

1206 F05c

Differential Input Signal Swing

The differential input swing is limited to about ± 6V by

an ESD protection device connected between the inputs.

In normal operation, the differential voltage between the

input pins is small, so this clamp has no effect; however,

in the shutdown mode the differential swing can be the

same as the input swing. The clamp voltage will then set

500ns/DIV

1206 TA02