Electronic Components Datasheet Search |
|
LM334 Datasheet(PDF) 5 Page - National Semiconductor (TI) |
|
|
LM334 Datasheet(HTML) 5 Page - National Semiconductor (TI) |
5 / 14 page Typical Performance Characteristics (Continued) Application Hints The LM134 has been designed for ease of application, but a general discussion of design features is presented here to familiarize the designer with device characteristics which may not be immediately obvious. These include the effects of slewing, power dissipation, capacitance, noise, and con- tact resistance. CALCULATING R SET The total current through the LM134 (I SET) is the sum of the current going through the SET resistor (I R) and the LM134’s bias current (I BIAS), as shown in Figure 1. A graph showing the ratio of these two currents is supplied under Ratio of I SET to IBIAS in the Typical Performance Characteristics section. The current flowing through R SET is determined by V R, which is approximately 214µV/˚K (64 mV/ 298˚K ∼ 214µV/˚K). Since (for a given set current) I BIAS is simply a percentage of I SET, the equation can be rewritten where n is the ratio of I SET to IBIAS as specified in the Elec- trical Characteristics Section and shown in the graph. Since n is typically 18 for 2µA ≤ I SET ≤ 1mA, the equation can be further simplified to for most set currents. SLEW RATE At slew rates above a given threshold (see curve), the LM134 may exhibit non-linear current shifts. The slewing rate at which this occurs is directly proportional to I SET.At I SET = 10µA, maximum dV/dt is 0.01V/µs; at ISET = 1mA, the limit 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 regu- lation for I SET greater than 100µA. For example, each 1V in- crease across the LM134 at I SET = 1 mA will increase junc- tion temperature by ≈0.4˚C in still air. Output current (I SET) 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 compared to true electrical effects. Thermal effects, therefore, must be taken into account when DC regulation is critical and I SET exceeds 100µA. Heat sinking of the TO-46 package or the TO-92 leads can reduce this effect by more than 3:1. SHUNT CAPACITANCE In certain applications, the 15 pF 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 an FET as shown in the applications. This can reduce capacitance to less than 3 pF and improve regu- lation by at least an order of magnitude. DC characteristics (with the exception of minimum input voltage), are not af- fected. Turn-On Voltage DS005697-29 Ratio of I SET to IBIAS DS005697-3 DS005697-27 FIGURE 1. Basic Current Source www.national.com 5 |
Similar Part No. - LM334 |
|
Similar Description - LM334 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List 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 |