Electronic Components Datasheet Search |
|
LT1585CM Datasheet(PDF) 8 Page - Linear Technology |
|
LT1585CM Datasheet(HTML) 8 Page - Linear Technology |
8 / 12 page 8 LT1584/LT1585/LT1587 APPLICATIONS INFORMATION 100 µF aluminum covers all cases of bypassing the adjust terminal. With no adjust pin bypassing, smaller values of capacitors provide equally good results. Normally, capacitor values on the order of several hundred microfarads are used on the output of the regulators to ensure good transient response with heavy load current changes. Output capacitance can increase without limit and larger values of output capacitance further improve the stability and transient response of the LT1584/LT1585/ LT1587 family. Large load current changes are exactly the situation pre- sented by modern microprocessors. The load current step contains higher order frequency components that the output decoupling network must handle until the regulator throttles to the load current level. Capacitors are not ideal elements and contain parasitic resistance and inductance. These parasitic elements dominate the change in output voltage at the beginning of a transient load step change. The ESR of the output capacitors produces an instanta- neous step in output voltage ( ∆V = ∆I × ESR). The ESL of the output capacitors produces a droop proportional to the rate of change of output current (V = L × ∆I/∆t). The output capacitance produces a change in output voltage propor- tional to the time until the regulator can respond ( ∆V = ∆t × ∆I/C). These transient effects are illustrated in Figure 1. network is actually inside the microprocessor socket cav- ity. In addition, use large power and ground plane areas to minimize distribution drops. A possible stability problem that occurs in monolithic linear regulators is current limit oscillations. The LT1585/LT1587 essentially have a flat current limit over the range of input supply voltage. The lower current limit rating and 7V maximum supply voltage rating for these devices permit this characteristic. Current limit oscillations are typically nonexistent, unless the input and output decoupling ca- pacitors for the regulators are mounted several inches from the terminals. The LT1584 differs from the LT1585/ LT1587 and provides current limit foldback as input-to- output differential voltage increases. This safe-area char- acteristic exhibits a negative impedance because increas- ing voltage causes output current to decrease. Negative resistance during current limit is not unique to the LT1584 devices and is present on many power IC regulators. The value of the negative resistance is a function of how fast the current limit is folded back as input-to-output voltage increases. This negative resistance can react with capaci- tors and inductors on the input and output to cause oscillation during current limit. Depending on the values of series resistances, the overall system may end up unstable. However, the oscillation causes no problem and the IC remains protected. In general, if this problem occurs and is unacceptable, increasing the amount of output capacitance helps dampen the system. Protection Diodes In normal operation, the LT1584/LT1585/LT1587 family does not require any protection diodes. Older three-termi- nal regulators require protection diodes between the out- put pin and the input pin or between the adjust pin and the output pin to prevent die overstress. On the adjustable LT1584/LT1585/LT1587, internal resis- tors limit internal current paths on the adjust pin. Therefore, even with bypass capacitors on the adjust pin, no protec- tion diode is needed to ensure device safety under short- circuit conditions. A protection diode between the input and output pins is usually not needed. An internal diode between the input and output pins on the LT1584/LT1585/LT1587 family can Figure 1 ESR EFFECTS LT1584 • F01 ESL EFFECTS CAPACITANCE EFFECTS POINT AT WHICH REGULATOR TAKES CONTROL SLOPE, = V t ∆I C The use of capacitors with low ESR, low ESL, and good high frequency characteristics is critical in meeting the output voltage tolerances of these high speed microprocessors. These requirements dictate a combination of high quality, surface mount tantalum capacitors and ceramic capaci- tors. The location of the decoupling network is critical to transient response performance. Place the decoupling network as close as possible to the processor pins because trace runs from the decoupling capacitors to the processor pins are inductive. The ideal location for the decoupling |
Similar Part No. - LT1585CM |
|
Similar Description - LT1585CM |
|
|
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 |