データシートサーチシステム |
|
LM134H データシート(PDF) 5 Page - Linear Technology |
|
LM134H データシート(HTML) 5 Page - Linear Technology |
5 / 12 page LM134 Series 5 APPLICATIO S I FOR ATIO Basic Theory of Operation The equivalent circuit of the LM134 is shown in Figure 1. A reference voltage of 64mV is applied to the minus input of A1 with respect to the V– pin. A1 serves the drive to Q2 to keep the R pin at 64mV, independent of the value of RSET. Transistor Q1 is matched to Q2 at a 17:1 ratio so that the current flowing out of the V– pin is always 1/18 of the total current into the V+ pin. This total current is called ISET and is equal to: 64 18 17 67 7 mV R mV R SET SET = . Figure 1. The 67.7mV equivalent reference voltage is directly pro- portional to absolute temperature in degrees Kelvin (see curve, “Operating Current vs Temperature”). This means that the reference voltage can be plotted as a straight line going from 0mV at absolute zero temperature to 67.7mV at 298 °K (25°C). The slope of this line is 67.7mV/298 = 227 µV/°C. The accuracy of the device is specified as a percent error at room temperature, or in the case of the -3 and -6 devices, as both a percent error and an equivalent tem- perature error. The LM134 operating current changes at a percent rate equal to (100)(227 µV/°C)/(67.7mV)=0.336%/ °C at 25°C, so each 1% operating current error is equiva- lent to ≈3°C temperature error when the device is used as a temperature sensor. The slope accuracy (temperature coefficient) of the LM134 is expressed as a ratio com- pared to unity. The LM134-3, for instance, is specified at 0.98 to 1.02, indicating that the maximum slope error of – + + – RSET ISET 64mV A1 R V– V+ Q2 Q1 134 F01 the device is ±2% when the room temperature current is set to the exact desired value. Supply Voltage Slew Rate At slew rates above a given threshold (see curve), the LM134 may exhibit nonlinear current shifts. The slewing rate at which this occurs is directly proportional to ISET. At ISET = 10µA, maximum dv/dt is 0.01V/µs; at ISET = 1mA, the limits is 1V/ µs. Slew rates above the limit do not harm the LM134, or cause large currents to flow. Thermal Effects Internal heating can have a significant effect on current regulation for ISET greater than 100µA. For example, each 1V increase across the LM134 at ISET = 1mA will increase junction temperature by ≈0.4°C in still air. Output current (ISET) has a temperature coefficient of ≈0.33%/°C, so the change in current due to temperature rise will be (0.4)(0.33) = 0.132%. This is a 10:1 degradation in regulation com- pared to true electrical effects. Thermal effects, therefore, must be taken into account when DC regulation is critical and ISET exceeds 100µA. Heat sinking of the TO-46 pack- age or the TO-92 leads can reduce this effect by more than 3:1. Shunt Capacitance In certain applications, the 15pF shunt capacitance of the LM134 may have to be reduced, either because of loading problems or because it limits the AC output impedance of the current source. This can be easily accomplished by buffering the LM134 with a FET, as shown in the applica- tions. This can reduce capacitance to less than 3pF and improve regulation by at least an order of magnitude. DC characteristics (with the exception of minimum input voltage) are not affected. Noise Current noise generated by the LM134 is approximately 4 times the shot noise of a transistor. If the LM134 is used as an active load for a transistor amplifier, input referred noise will be increased by about 12dB. In many cases, this is acceptable and a single stage amplifier can be built with a voltage gain exceeding 2000. |
同様の部品番号 - LM134H |
|
同様の説明 - LM134H |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |