Datasheet LT1226 (Analog Devices) - 6

LT1226
O U U W U APPLICATI S I FOR ATIO
The LT1226 may be inserted directly into HA2541, HA2544,
Small Signal, AV = +25 Small Signal, AV = – 25
AD847, EL2020 and LM6361 applications, provided that the amplifier configuration is a noise gain of 25 or greater, and the nulling circuitry is removed. The suggested nulling circuit for the LT1226 is shown below.
Offset Nulling
V+ 5k LT1226 AI02 0.1µF 1 The large signal response in both inverting and noninvert- 3 + 8 ing gain shows symmetrical slewing characteristics. Nor- 7 6 LT1226 mally the noninverting response has a much faster rising 2 – 4 edge due to the rapid change in input common mode 0.1µF voltage which affects the tail current of the input differen- V – tial pair. Slew enhancement circuitry has been added to LT1226 AI01 the LT1226 so that the falling edge slew rate is enhanced
Layout and Passive Components
which balances the noninverting slew rate response. As with any high speed operational amplifier, care must be
Large Signal, AV = +25 Large Signal, AV = – 25
taken in board layout in order to obtain maximum perfor- mance. Key layout issues include: use of a ground plane, minimization of stray capacitance at the input pins, short lead lengths, RF-quality bypass capacitors located close to the device (typically 0.01µF to 0.1µF), and use of low ESR bypass capacitors for high drive current applications (typically 1µF to 10µF tantalum). Sockets should be avoided when maximum frequency performance is LT1226 AI03 required, although low profile sockets can provide
Input Considerations
reasonable performance up to 50MHz. For more details Resistors in series with the inputs are recommended for see Design Note 50. Feedback resistors greater than 5kΩ the LT1226 in applications where the differential input are not recommended because a pole is formed with the voltage exceeds ±6V continuously or on a transient basis. input capacitance which can cause peaking. If feedback An example would be in noninverting configurations with resistors greater than 5kΩ are used, a parallel high input slew rates or when driving heavy capacitive capacitor of 5pF to 10pF should be used to cancel the input loads. The use of balanced source resistance at each input pole and optimize dynamic performance. is recommended for applications where DC accuracy
Transient Response
must be maximized. The LT1226 gain bandwidth is 1GHz when measured at
Capacitive Loading
1MHz. The actual frequency response in a gain of +25 is The LT1226 is stable with all capacitive loads. This is considerably higher than 40MHz due to peaking caused by accomplished by sensing the load induced output pole a second pole beyond the gain of 25 crossover point. This and adding compensation at the amplifier gain node. As is reflected in the small signal transient response. Higher the capacitive load increases, both the bandwidth and noise gain configurations exhibit less overshoot as seen in phase margin decrease so there will be peaking in the the inverting gain of 25 response. 6