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LT1210X

1210Xfa

For more information www.linear.com/LT1210X

APPLICATIONS INFORMATION

PIN FUNCTIONS

The LT1210X is a current feedback amplifier with high

output current drive capability. The device is stable with

large capacitive loads and can easily supply the high cur-

rents required by capacitive loads. The amplifier will drive

low impedance loads such as cables with excellent linear-

ity at high frequencies.

Feedback Resistor Selection

The optimum value for the feedback resistors is a function

of the operating conditions of the device, the load imped-

ance and the desired flatness of response. The Typical AC

Performance tables give the values which result in less

than 1dB of peaking for various resistive loads and oper-

ating conditions. If this level of flatness is not required,

a higher bandwidth can be obtained by use of a lower

feedback resistor. The characteristic curves of Bandwidth

vs Supply Voltage indicate feedback resistors for peak-

ing up to 5dB. These curves use a solid line when the

response has less than 1dB of peaking and a dashed line

when the response has 1dB to 5dB of peaking. The curves

stop where the response has more than 5dB of peaking.

For resistive loads, the COMP pin should be left open (see

Capacitive Loads section).

V+ (Pins 1, 8, 9, 16, 17): Positive Supply Voltage. V+ and

V– must be chosen so that 10V ≤ (V+ – V–) < 36V.

NC (Pins 2, 4, 5, 7, 10, 15): No Connection. These pins

are floating, with no internal connection.

OUT (Pin 3): Amplifier Output. The output can source/sink

a minimum of 1A over temperature.

-IN (Pin 6): Inverting Input of Amplifier. Valid input range

is ±12V on ±15V supplies.

+IN (Pin 11): Non-Inverting Input of Amplifier. Valid input

range is ±12V on ±15V supplies.

SHUTDOWN (Pin 12): If the shutdown feature is not

used, the SHUTDOWN pin must be connected to Ground

or V–. The SHUTDOWN pin can be used to either turn

off the biasing for the amplifier, reducing the quiescent

current to less than 200A, or to control the quiescent

current in normal operation. For more information, refer

to the Shutdown/Current Set section in the Applications

Information.

COMP (Pin 13): Adding a 0.01µF capacitor between the

output and the COMP pin greatly reduces peaking when

driving capacitive loads. To disconnect the optional com-

pensation, leave the COMP pin open. For more infor-

mation, refer to the Capacitive Loads section in the

Applications Information.

V– (Pin 14): Negative Supply Voltage. V+ and V– must be

chosen so that 10V ≤ (V+ – V–) < 36V.

Capacitive Loads

The LT1210X includes an optional compensation network

for driving capacitive loads. This network eliminates most

of the output stage peaking associated with capacitive

loads, allowing the frequency response to be flattened.

Figure 1 shows the effect of the network on a 200pF load.

Without the optional compensation, there is a 6dB peak

at 40MHz caused by the effect of the capacitance on the

output stage. Adding a 0.01µF bypass capacitor between

the output and the COMP pins connects the compensation

and greatly reduces the peaking. A lower value feedback

resistor can now be used, resulting in a response which

is flat to ±1dB to 40MHz. The network has the greatest

effect for CL in the range of 0pF to 1000pF. The graphs of

Bandwidth and Feedback Resistance vs Capacitive Load

can be used to select the appropriate value of feedback

resistor. The values shown are for 1dB and 5dB peaking at

a gain of 2 with no resistive load. This is a worst-case con-

dition, as the amplifier is more stable at higher gains and

with some resistive load in parallel with the capacitance.

Also shown is the –3dB bandwidth with the suggested

feedback resistor vs the load capacitance.

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