Datasheet LT1358, LT1359 (Analog Devices) - 10

LT1358/LT1359
U U W U APPLICATIO S I FOR ATIO Layout and Passive Components Input Considerations
The LT1358/LT1359 amplifiers are easy to use and toler- Each of the LT1358/LT1359 inputs is the base of an NPN ant of less than ideal layouts. For maximum performance and a PNP transistor whose base currents are of opposite (for example, fast 0.01% settling) use a ground plane, polarity and provide first-order bias current cancellation. short lead lengths, and RF-quality bypass capacitors Because of variation in the matching of NPN and PNP beta, (0.01µF to 0.1µF). For high drive current applications use the polarity of the input bias current can be positive or low ESR bypass capacitors (1µF to 10µF tantalum). negative. The offset current does not depend on NPN/PNP beta matching and is well controlled. The use of balanced The parallel combination of the feedback resistor and gain source resistance at each input is recommended for setting resistor on the inverting input combine with the applications where DC accuracy must be maximized. input capacitance to form a pole which can cause peaking or oscillations. If feedback resistors greater than 5k are The inputs can withstand transient differential input volt- used, a parallel capacitor of value ages up to 10V without damage and need no clamping or source resistance for protection. Differential inputs, how- CF > RG x CIN / RF ever, generate large supply currents (tens of mA) as required for high slew rates. If the device is used with should be used to cancel the input pole and optimize sustained differential inputs, the average supply current dynamic performance. For unity-gain applications where will increase, excessive power dissipation will result and a large feedback resistor is used, CF should be greater than the part may be damaged.
The part should not be used
or equal to CIN.
as a comparator, peak detector or other open-loop application with large, sustained differential inputs
.
Capacitive Loading
Under normal, closed-loop operation, an increase of power The LT1358/LT1359 are stable with any capacitive load. dissipation is only noticeable in applications with large As the capacitive load increases, both the bandwidth and slewing outputs and is proportional to the magnitude of phase margin decrease so there will be peaking in the the differential input voltage and the percent of the time frequency domain and in the transient response. Coaxial that the inputs are apart. Measure the average supply cable can be driven directly, but for best pulse fidelity a current for the application in order to calculate the power resistor of value equal to the characteristic impedance of dissipation. the cable (i.e., 75Ω) should be placed in series with the output. The other end of the cable should be terminated with the same value resistor to ground. 135859fb 10