Zakładka z wyszukiwarką danych komponentów |
|
LM3103 Arkusz danych(PDF) 9 Page - Texas Instruments |
|
LM3103 Arkusz danych(HTML) 9 Page - Texas Instruments |
9 / 20 page VIN 8.3 x 10 -11 x R ON tON = VOUT 8.3 x 10 -11 x R ON fSW = (VIN ± VOUT) x RON 2 VOUT (VIN - 1) x L x 1.18 x 10 20 x I OUT fSW = LM3103 www.ti.com SNVS523E – SEPTEMBER 2007 – REVISED NOVEMBER 2009 The regulator will operate in the discontinuous conduction mode (DCM) at a light load, and the continuous conduction mode (CCM) with a heavy load. In the DCM, the current through the inductor starts at zero and ramps up to a peak during the on-time, and then ramps back to zero before the end of the off-time. It remains zero and the load current is supplied entirely by the output capacitor. The next on-time period starts when the voltage at the FB pin falls below the internal reference. The operating frequency in the DCM is lower and varies larger with the load current as compared with the CCM. Conversion efficiency is maintained since conduction loss and switching loss are reduced with the reduction in the load and the switching frequency respectively. The operating frequency in the DCM can be calculated approximately as follows: (1) In the continuous conduction mode (CCM), the current flows through the inductor in the entire switching cycle, and never reaches zero during the off-time. The operating frequency remains relatively constant with load and line variations. The CCM operating frequency can be calculated approximately as follows: (2) The output voltage is set by two external resistors RFB1 and RFB2. The regulated output voltage is VOUT = 0.6V x (RFB1 + RFB2)/RFB2 (3) Startup Regulator (VCC) A startup regulator is integrated within the LM3103. The input pin VIN can be connected directly to a line voltage up to 42V. The VCC output regulates at 6V, and is current limited to 30 mA. Upon power up, the regulator sources current into an external capacitor CVCC, which is connected to the VCC pin. For stability, CVCC must be at least 1 µF. When the voltage on the VCC pin is higher than the under-voltage lock-out (UVLO) threshold of 3.7V, the main MOSFET is enabled and the SS pin is released to allow the soft-start capacitor CSS to charge. The minimum input voltage is determined by the dropout voltage of the regulator and the VCC UVLO falling threshold ( ≊3.4V). If VIN is less than ≊4.0V, the regulator shuts off and VCC goes to zero. Regulation Comparator The feedback voltage at the FB pin is compared to a 0.6V internal reference. In normal operation (the output voltage is regulated), an on-time period is initiated when the voltage at the FB pin falls below 0.6V. The main MOSFET stays on for the programmed on-time, causing the output voltage to rise and consequently the voltage of the FB pin to rise above 0.6V. After the on-time period, the main MOSFET stays off until the voltage of the FB pin falls below 0.6V again. Bias current at the FB pin is nominally 1 nA. Zero Coil Current Detect The current of the synchronous MOSFET is monitored by a zero coil current detection circuit which inhibits the synchronous MOSFET when its current reaches zero until the next on-time. This circuit enables the DCM operation, which improves the efficiency at a light load. Over-Voltage Comparator The voltage at the FB pin is compared to a 0.68V internal reference. If it rises above 0.68V, the on-time is immediately terminated. This condition is known as over-voltage protection (OVP). It can occur if the input voltage or the output load changes suddenly. Once the OVP is activated, the main MOSFET remains off until the voltage at the FB pin falls below 0.6V. The synchronous MOSFET will stay on to discharge the inductor until the inductor current reduces to zero and then switch off. ON-Time Timer, Shutdown The on-time of the LM3103 main MOSFET is determined by the resistor RON and the input voltage VIN. It is calculated as follows: (4) Copyright © 2007–2009, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM3103 |
Podobny numer części - LM3103_14 |
|
Podobny opis - LM3103_14 |
|
|
Link URL |
Polityka prywatności |
ALLDATASHEET.PL |
Czy Alldatasheet okazała się pomocna? [ DONATE ] |
O Alldatasheet | Reklama | Kontakt | Polityka prywatności | Linki | Lista producentów 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 |