Electronic Components Datasheet Search |
|
SP6655 Datasheet(PDF) 9 Page - Sipex Corporation |
|
SP6655 Datasheet(HTML) 9 Page - Sipex Corporation |
9 / 16 page 9 Date: 7/12/04 SP6655 High Efficiency 400mA Synchronous Buck Regulator © Copyright 2004 Sipex Corporation point RESET is held low until VOUT is above regulation. Once RESET occurs TON minimum is reset, and the TOFF one-shot is triggered to blank the loop comparator from starting a new charge cycle for a minimum period. This blank- ing period occurs during the noisy LX transition to discharge, where spurious comparator states may occur. For TOFF > TBLANK the loop is in a discharge or wait state until the loop comparator starts the next charge cycle by DRVON going high. If an over current occurs during charge the loop is interrupted and DRVON is RESET. The off- time one-shot pulse width is widened to TOFF = KOFF / VOUT, which holds the loop in discharge for that time. At the end of the off-time the loop is released and controlled by VOLOW. In this manner maximum inductor current is controlled on a cycle-by-cycle basis. An assertion of UVLO (undervoltage lockout) or TSD (thermal shut- down) holds the loop in no-charge until the fault has ended. On-Time Control - Discharge Phase The discharge phase follows with the high side PMOS switch opening and the low side NMOS switch closing to provide a discharge path for the inductor current. The decreasing inductor current and the load current cause the output voltage to drop. Under normal load conditions when the inductor current is below the pro- grammed limit, the off-time will continue until the output voltage falls below the regulation threshold, which initiates a new charge cycle via the loop comparator. The inductor current “floats” in continuous con- duction mode. During this mode the inductor peak current is below the programmed limit and the valley current is above zero. This is to satisfy load currents that are greater than half the mini- mum current ripple. The current ripple, ILR, is defined by the equation: ILR ≈ KON * VIN - VOUT - IOUT * RCH L VIN - VOUT where: L = Inductor value IOUT = Load current RCH = PMOS on resistance, 0.3Ω typ. If the IOUT * RCH term is negligible compared with (VIN - VOUT), the above equation simplifies to: ILR ≈ KON L For most applications, the inductor current ripple controlled by the SP6655 is constant regardless of input and output voltage. Because the output voltage ripple is equal to: VOUT (ripple) = ILR * RESR where: RESR = ESR of the output capacitor the output ripple of the SP6655 regulator is independent of the input and output voltages. For battery powered applications, where the battery voltage changes significantly, the SP6655 provides constant output voltage ripple through- out the battery lifetime. This greatly simplifies the LC filter design. The maximum loop frequency in CCM is de- fined by the equation: FLP ≈ (VIN - VOUT) * (VOUT + IOUT * RDC) KON * [VIN + IOUT * (RDC - RCH)] where: FLP = CCM loop frequency RDC = NMOS on resistance, 0.3Ω typ. Ignoring conduction losses simplifies the loop frequency to: FLP ≈ 1 * VOUT * (VIN - VOUT) KON VIN AND’ing the loop comparator and the on-timer reduces the switching frequency for load cur- rents below half the inductor ripple current. This increases light load efficiency. The minimum on-time insures that the inductor current ripple THEORY OF OPERATION |
Similar Part No. - SP6655 |
|
Similar Description - SP6655 |
|
|
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 |