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LM134D データシート(PDF) 5 Page - STMicroelectronics |
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LM134D データシート(HTML) 5 Page - STMicroelectronics |
5 / 10 page APPLICATION HINT SLEW RATE At slew rates above a threshold (see curve) the LM134, LM234, LM334 can have a non-linear cur- rent characteristic. The slew rate at which this takes place is directly proportional to Iset.At Iset =10 µA, dv/dt max. = 0.01V/ µS ; at Iset = 1mA, dv/dt max. = 1V/ µS. Slew rates of more than 1V/µSdo not dam- age the circuit nor do they produce high currents. THERMAL EFFECTS Internal heating can have a significant effect on cur- rent regulation for an Iset above 100 µA. For exam- ple, each increase of 1V in the voltage across the LM134 at Iset = 1mA will increase the junction tem- perature by ≈ 0.4oC (in still air). The output current (Iset) has a temperature coefficient of about 0.33%/ oC. Thus the change in current due to the in- crease in temperature will be (0.4) (0.33) = 0.132%. This is a degradation of 10 : 1 in regulation versus the true electrical effects. Thermal effects should be taken into account when d.c. regulation is critical and Iset is higher than 100 µA. The dissipation of the connectionsof CB-97 packagecan reduce this ther- mal effect by a coefficient of more than 3. SHUNT CAPACITANCE In certain applications, the 15pF value for the shunt capacitance should be reduced : - because of loading problems, - because of limitation of the output impedance of the current source in a.c. applications. This reduc- tion of the capacitance can be easily carried out by adding a FET as indicatedin the typical applications. The value of this capacitance can be reduced by at least 3pF and regulation can be improved by an or- der of magnitude without any modificationof the d.c. characteristics (except for the minimum input volt- age). NOISE The current noise produced by LM134, LM234, LM334 is about 4 times that of a transistor. If the LM134, LM234, LM334 is utilized as an active load for a transistor amplifier, the noise at the input will increase by about 12dB. In most cases this is ac- ceptable, and a single amplifier can be built with a voltage gain higher than 2000. LEAD RESISTANCE The sense voltage which determines the current of the LM134, LM234, LM334, is less than 100mV. At this level, the effects of the thermocouple and the connection resistance should be reduced by locat- ing the current setting resistor close to the device. Do not use sockets for the ICs. A contact resistance of 0.7 Ω is sufficient to decrease the output current by 1% at the 1mA level. SENSING TEMPERATURE The LM134, LM234, LM334 are excellent remote controlled temperature sensors because their op- eration as sources of current preserves their accu- racy even in the case of long connecting wires. The output current is directly proportional to the absolute temperature in degrees Kelvin according to the fol- lowing equation. Iset = ( 227 µV/oK)(T) Rset The calibration of the LM134, LM234, LM334 is sim- plified by the fact that most of the initial accuracy is due to gain limitation (slope error) and not an offset. Gain adjustment is a one point trim because the out- put of the device extrapolates to zero at 0 oK. This particularity of the LM134, LM234, LM334 is il- lustrated in the above diagram. Line abc represents the sensor current before adjustment and line a’b’c’ represents the desired output. An adjustment of the gain provided at T2 will move the output from b to b’ and will correct the slope at the same time so that the output at T1 and T3 will be correct. This gain ad- justment can be carried out by means of Rset or the load resistor utilized in the circuit. After adjustment, the slope error should be less than 1%. A low tem- peraturecoefficient for Rset is necessary to keep this accuracy. A 33ppm/ oC temperature drift of Rset will give an error of 1% on the slope because the resis- tance follows the same temperature variations as the LM134, LM234, LM334. Three wires are re- quired to isolate Rset from the LM134, LM234, LM334. Since this solution is not recommended. Metal-film resistors with a drift less than 20ppm/ oC are now available. Wirewound resistors can be util- ized when very high stability is required. T1 T2 T3 0 °K I set Desired output Initial output c b a a’ b’ c’ LM134-LM234-LM334 5/10 |
同様の部品番号 - LM134D |
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同様の説明 - LM134D |
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