Os motores de busca de Datasheet de Componentes eletrônicos |
|
LM3557 Folha de dados(PDF) 5 Page - National Semiconductor (TI) |
|
|
LM3557 Folha de dados(HTML) 5 Page - National Semiconductor (TI) |
5 / 11 page Operation (Continued) An increase in inductor current corresponds to an increase in the amount of stored energy within the inductor. Conversely, a decrease in inductor current corresponds to a decrease in the amount of stored energy. The inductor’s stored energy is released, or transferred, to the load when the N1 power FET is turned off. The transferred inductor energy replenishes the output capacitor and keeps the white LED current regulated at the designated magnitude that is based on the choice of the R2 resistor. When the N1 power FET is turned on, the energy stored within the inductor begins to increase while the output capacitor discharges through the series string of white LEDs, the R2 resistance, and N2 FET switch to ground. Therefore, each switching cycle consist of some amount of energy being stored in the inductor that is then released, or transferred, to the load to keep the voltage at the feedback pin in regulation at 510 mV above the Sw2 pin voltage. Features: CYCLE-BY-CYCLE CURRENT LIMIT The current through the internal power FET (Figure 2: N1) is monitored to prevent peak inductor currents from damaging the part. If during a cycle (cycle = 1/switching frequency) the peak inductor current exceeds the current limit rating for the LM3557, the internal power FET would be forcibly turned off for the remaining duration of that cycle. OVER-VOLTAGE PROTECTION When the output voltage exceeds the over-voltage protec- tion (OVP) threshold, the LM3557’s internal power FET will be forcibly turned off until the output voltage falls below the over-voltage protection threshold minus the 500 mV hyster- esis of the internal OVP circuitry. UNDER-VOLTAGE PROTECTION When the input voltage falls below the under-voltage protec- tion (UVP) threshold, the LM3557’s internal power FET will be forcibly turned off until the input voltage is above the designated under-voltage protection threshold plus the 100 mV hysteresis of the internal UVP circuitry. TRUE SHUTDOWN When the LM3557 is put into shutdown mode operation there are no DC current paths to ground. The internal FET (Figure 2: N2) at the Sw2 pin turns off, leaving the white LED string open circuited. THERMAL SHUTDOWN When the internal semiconductor junction temperature reaches approximately 150˚C, the LM3557’s internal power FET (Figure 2: N1) will be forcibly turned off. Typical Performance Characteristics ( Circuit in Figure 1: L = DO1608C-223, D = SS16, and LED = LWT67C. Efficiency: η =P OUT/PIN = [(VOUT –VFb)*IOUT]/[VIN *IIN]. TA= 25˚C, unless otherwise stated). I Q (SWITCHING) vs TEMPERATURE SWITCHING FREQUENCY vs TEMPERATURE 20131604 20131605 www.national.com 5 |
Nº de peça semelhante - LM3557 |
|
Descrição semelhante - LM3557 |
|
|
Ligação URL |
Privacy Policy |
ALLDATASHEETPT.COM |
ALLDATASHEET é útil para você? [ DONATE ] |
Sobre Alldatasheet | Publicidade | Contato conosco | Privacy Policy | roca de Link | Lista de Fabricantes 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 |