Moteur de recherche de fiches techniques de composants électroniques |
|
LM3570SD Fiches technique(PDF) 10 Page - National Semiconductor (TI) |
|
|
LM3570SD Fiches technique(HTML) 10 Page - National Semiconductor (TI) |
10 / 13 page Application Information PRE-REGULATION The very low input current ripple of the LM3570, resulting from internal pre-regulation, adds very little noise to the input line. The core of the LM3570 is very similar to that of a basic 3/2 switched capacitor regulator: it is composed of seven switches and two flying capacitors (external). Regulation is achieved by modulating the on-resistance of the three switches connected to the input pin (one switch in phase one and two in phase two). The regulation is done before the voltage “gain stage”, giving rise to the term "pre-regulation". Pre-regulation eliminates most of the input current ripple that is a typical and undesirable characteristic of many switched capacitor converters. TOTAL OUTPUT CURRENT CAPABILITY The LM3570 is capable of providing a total output current of 80mA. The 80mA can be divided through any combination of the three dedicated current outputs and/or current drawn from the V OUT output. When pulling current from the VOUT pin, the LM3570 will hold the output voltage at the regulated 4.35V. This pre-regulation occurs when the input voltage is within the 3.0V to 5.5V operating range. If the input voltage is between the 2.7V to 3.0V range, the V OUT voltage will be- have in the same manner as the output of an unregulated charge pump. During operation in this input voltage range, the output voltage becomes directly related to the total out- put current drawn from the part and the output resistance (R OUT) of the charge pump. Figure 1 displays how the LM3570’s R OUT is modeled to solve for the VOUT voltage V OUT =(VINx1.5)-((IDx-Total+IOUT)xROUT) where 2.7V ≤ V IN < 3.0V and ROUT=4 Ω Dx OUTPUT CURRENT CAPABILITY An external resistor, R SET, is connected to the ISET pin to set the current to be mirrored in each of the three LED outputs. The internal current mirror sets each LED output current with a 100:1 ratio to the current through R SET. The current mirror circuitry matches the current through each LED to within 0.5%. An equation for approximating the LED current is: R SET=100 x (1.25V / IDX) PARALLEL Dx OUTPUTS FOR INCREASED CURRENT CAPABILITY Outputs D 1 through D3 may be connected together in any combination to drive higher currents through fewer LEDs. For example in Figure 2, outputs D 2 and D3 are connected together to drive one LED while D 1 is connected to a seper- ate LED. With this configuration, two parallel current sources of equal value provide current to one of the LEDs. R SET should therefore be chosen so that the current through each output is programmed to 50% of the desired current through the parallel connected LED. For example, if 40mA is the desired drive current for the parallel connected LED, R SET should be selected so that the current through each of the outputs is 20mA. Other combinations of parallel outputs may be imple- mented in similar fashions, such as in Figure 3. Connecting outputs in parallel does not affect internal opera- tion of the LM3570 and has no impact on the Electrical 20085004 FIGURE 1. LM3570 Charge Pump Model 20085007 FIGURE 2. One Parallel Connected and One Singular Connected LED 20085006 FIGURE 3. One Parallel Connected LED www.national.com 10 |
Numéro de pièce similaire - LM3570SD |
|
Description similaire - LM3570SD |
|
|
Lien URL |
Politique de confidentialité |
ALLDATASHEET.FR |
ALLDATASHEET vous a-t-il été utile ? [ DONATE ] |
À propos de Alldatasheet | Publicité | Contactez-nous | Politique de confidentialité | Echange de liens | Fabricants 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 |