Electronic Components Datasheet Search |
|
LX8554-XX Datasheet(PDF) 5 Page - Microsemi Corporation |
|
LX8554-XX Datasheet(HTML) 5 Page - Microsemi Corporation |
5 / 7 page 5A EXTREMELY LOW DROPOUT POSITIVE REGULATORS LX8554-xx PRODUCT DA T ABOOK 1996/1997 5 Copyright © 1997 Rev. 1.1 1/97 P RODUCTION D AT A S HEET APPLICA TION NOTES FIGURE 2 — BASIC ADJUSTABLE REGULATOR R2+R1 R1 LX8554 OUT IN ADJ V OUT V IN R1 R2 V REF I ADJ 50µA V OUT = VREF 1 + + I ADJ R2 R2 R1 OVERLOAD RECOVERY (continued) If this limited current is not sufficient to develop the designed voltage across the output resistor, the voltage will stabilize at some lower value, and will never reach the designed value. Under these circumstances, it may be necessary to cycle the input voltage down to zero in order to make the regulator output voltage return to regulation. RIPPLE REJECTION Ripple rejection can be improved by connecting a capacitor between the ADJ pin and ground. The value of the capacitor should be chosen so that the impedance of the capacitor is equal in magnitude to the resistance of R1 at the ripple frequency. The capacitor value can be determined by using this equation: C = 1 / (6.28 * F R * R1) where: C ≡ the value of the capacitor in Farads; select an equal or larger standard value. F R ≡ the ripple frequency in Hz R1 ≡ the value of resistor R1 in ohms At a ripple frequency of 120Hz, with R1 = 100 Ω: C = 1 / (6.28 * 120Hz * 100Ω) = 13.3µF The closest equal or larger standard value should be used, in this case, 15µF. When an ADJ pin bypass capacitor is used, output ripple amplitude will be essentially independent of the output voltage. If an ADJ pin bypass capacitor is not used, output ripple will be proportional to the ratio of the output voltage to the reference voltage: M = V OUT/VREF where: M ≡ a multiplier for the ripple seen when the ADJ pin is optimally bypassed. V REF = 1.25V. For example, if V OUT = 2.5V the output ripple will be: M = 2.5V/1.25V= 2 Output ripple will be twice as bad as it would be if the ADJ pin were to be bypassed to ground with a properly selected capacitor. OUTPUT VOLTAGE The LX8554 develops a 1.25V reference voltage between the output and the adjust terminal (See Figure 2). By placing a resistor, R1, between these two terminals, a constant current is caused to flow through R1 and down through R2 to set the overall output voltage. Normally this current is the specified minimum load current of 10mA. Because I ADJ is very small and constant when compared with the current through R1, it represents a small error and can usually be ignored. LOAD REGULATION Because the LX8554 is a three-terminal device, it is not possible to provide true remote load sensing. Load regulation will be limited by the resistance of the wire connecting the regulator to the load. The data sheet specification for load regulation is measured at the bottom of the package. Negative side sensing is a true Kelvin connection, with the bottom of the output divider returned to the negative side of the load. Although it may not be immediately obvious, best load regulation is obtained when the top of the resistor divider, (R1), is connected directly to the case of the regulator, not to the load. This is illustrated in Figure 3. If R1 were connected to the load, the effective resistance between the regulator and the load would be: R Peff = RP * where: R P ≡ Actual parasitic line resistance. When the circuit is connected as shown in Figure 3, the parasitic resistance appears as its actual value, rather than the higher R Peff. LX8554 OUT IN ADJ V IN R1 R2 R L R P Parasitic Line Resistance Connect R1 to Case of Regulator Connect R2 to Load FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION |
Similar Part No. - LX8554-XX |
|
Similar Description - LX8554-XX |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | 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 |