 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LM2590HV-AQ Datasheet(PDF) 19 Page - National Semiconductor (TI) |
|
|
||||||||||||||||||||||||||||||
LM2590HV-AQ Datasheet(HTML) 19 Page - National Semiconductor (TI) |
|
|
19 / 22 page  Application Information (Continued) tolerances, we should take the min value of Inductance for L in the equation above (typically 20% less than the nominal value). Further, the above equation disregards the drop across the Switch and the diode. This is equivalent to as- suming 100% efficiency, which is never so. Therefore expect I PEAK to be an additional 10-20% higher than calculated from the above equation. The reader is also referred to Application Note AN-1157 for examples based on positive to negative configuration. The maximum voltage appearing across the regulator is the absolute sum of the input and output voltage, and this must be limited to a maximum of 60V. In this example, when converting +20V to −5V, the regulator would see 25V be- tween the input pin and ground pin. The LM2590HV-AQ has a maximum input voltage rating of 60V. An additional diode is required in this regulator configuration. Diode D1 is used to isolate input voltage ripple or noise from coupling through the C IN capacitor to the output, under light or no load conditions. Also, this diode isolation changes the topology to closely resemble a buck configuration thus pro- viding good closed loop stability. A Schottky diode is recom- mended for low input voltages, (because of its lower voltage drop) but for higher input voltages, a IN5400 diode could be used. Because of differences in the operation of the inverting regulator, the standard design procedure is not used to select the inductor value. In the majority of designs, a 33 µH, 3A inductor is the best choice. Capacitor selection can also be narrowed down to just a few values. This type of inverting regulator can require relatively large amounts of input current when starting up, even with light loads. Input currents as high as the LM2590HV-AQ current limit (approximately 3.0A) are needed for 2 ms or more, until the output reaches its nominal output voltage. The actual time depends on the output voltage and the size of the output capacitor. Input power sources that are current limited or sources that can not deliver these currents without getting loaded down, may not work correctly. Because of the rela- tively high startup currents required by the inverting topology, the Soft-Start feature shown in Figure 10 is recommended. Also shown in Figure 10 are several shutdown methods for the inverting configuration. With the inverting configuration, some level shifting is required, because the ground pin of the regulator is no longer at ground, but is now at the negative output voltage. The shutdown methods shown accept ground referenced shutdown signals. UNDERVOLTAGE LOCKOUT Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage. Figure 11 contains a undervoltage lockout circuit for a buck configura- tion, while Figure 12 and Figure 13 are for the inverting types (only the circuitry pertaining to the undervoltage lockout is shown). Figure 11 uses a zener diode to establish the threshold voltage when the switcher begins operating. When the input voltage is less than the zener voltage, resistors R1 and R2 hold the Shutdown /Soft-start pin low, keeping the regulator in the shutdown mode. As the input voltage ex- ceeds the zener voltage, the zener conducts, pulling the Shutdown /Soft-start pin high, allowing the regulator to begin switching. The threshold voltage for the undervoltage lockout feature is approximately 1.5V greater than the zener voltage. Figure 12 and Figure 13 apply the same feature to an inverting circuit. Figure 12 features a constant threshold voltage for turn on and turn off (zener voltage plus approxi- mately one volt). If hysteresis is needed, the circuit in Figure 13 has a turn ON voltage which is different than the turn OFF voltage. The amount of hysteresis is approximately equal to the value of the output voltage. Since the SD /SS pin has an internal 7V zener clamp, R2 is needed to limit the current into this pin to approximately 1 mA when Q1 is on. LAYOUT SUGGESTIONS As in any switching regulator, layout is very important. Rap- idly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, with reference to Figure 1, the wires indicated by heavy lines should be wide 20097145 FIGURE 11. Undervoltage Lockout for a Buck Regulator 20097147 FIGURE 12. Undervoltage Lockout Without Hysteresis for an Inverting Regulator 20097146 FIGURE 13. Undervoltage Lockout With Hysteresis for an Inverting Regulator www.national.com 19 |
Similar Part No. - LM2590HV-AQ |
|
Similar Description - LM2590HV-AQ |
|
|
|
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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
