LT1809CS6 datasheet(17/24 Pages) LINER

17 / 24 page

LT1809/LT1810

APPLICATIO S I FOR ATIO

beyond either supply, unlimited current will flow through

these diodes. If the current is transient and limited to

several hundred milliamps, no damage to the device will

occur.

Overdrive Protection

When the input voltage exceeds the power supplies, two

pairs of crossing diodes, D1 to D4, will prevent the output

from reversing polarity. If the input voltage exceeds either

power supply by 700mV, diodes D1/D2 or D3/D4 will turn

on, keeping the output at the proper polarity. For the

phase reversal protection to perform properly, the input

current must be limited to less than 5mA. If the amplifier

is severely overdriven, an external resistor should be used

to limit the overdrive current.

The LT1809/LT1810’s input stages are also protected

against differential input voltages of 1.4V or higher by

back-to-back diodes, D5/D8, that prevent the emitter-base

breakdown of the input transistors. The current in these

diodes should be limited to less than 10mA when they are

active. The worst-case differential input voltage usually

occurs when the input is driven while the output is shorted

to ground in a unity-gain configuration. In addition, the

amplifier is protected against ESD strikes up to 3kV on all

pins by a pair of protection diodes on each pin that are

connected to the power supplies as shown in Figure 1.

Capacitive Load

The LT1809/LT1810 is optimized for high bandwidth and

low distortion applications. It can drive a capacitive load

about 20pF in a unity-gain configuration and more with

higher gain. When driving a larger capacitive load, a

resistor of 10

Ω to 50Ω should be connected between the

output and the capacitive load to avoid ringing or oscilla-

tion. The feedback should still be taken from the output so

that the resistor will isolate the capacitive load to ensure

stability. Graphs on capacitive loads indicate the transient

response of the amplifier when driving capacitive load with

a specified series resistor.

Feedback Components

When feedback resistors are used to set up gain, care must

be taken to ensure that the pole formed by the feedback

resistors and the total capacitance at the inverting input

does not degrade stability. For instance, the LT1809 in a

noninverting gain of 2, set up with two 1K resistors and a

capacitance of 3pF (device plus PC board), will probably

ring in transient response. The pole that is formed at

106MHz will reduce phase margin by 34 degrees when the

crossover frequency of the amplifier is around 70MHz. A

capacitor of 3pF or higher connected across the feedback

resistor will eliminate any ringing or oscillation.

SHDN Pin

The LT1809 has a SHDN pin to reduce the supply current

to less than 1.25mA. When the SHDN pin is pulled low, it

will generate a signal to power down the device. If the pin

is left unconnected, an internal pull-up resistor of 10k will

keep the part fully operating as shown in Figure 1. The

output will be high impedance during shutdown, and the

turn-on and turn-off time is less than 100ns. Because the

inputs are protected by a pair of back-to-back diodes, the

input signal will feed through to the output during shut-

down mode if the amplitude of signal between the inputs

is larger than 1.4V.

LT1809CS6 Datasheet(PDF) 17 Page - Linear Technology

LT1809CS6 Datasheet(HTML) 17 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL