Electronic Components Datasheet Search |
|
15032 Datasheet(PDF) 6 Page - Linear Technology |
|
15032 Datasheet(HTML) 6 Page - Linear Technology |
6 / 12 page 6 LTC1503-1.8/LTC1503-2 General Operation The two most common methods for providing regulated step-down DC/DC conversion are linear DC/DC conversion (used by LDOs) and inductor-based DC/DC conversion. Linear regulation provides low cost and low complexity, but the conversion efficiency is poor since all of the load cur- rent must come directly from VIN. Inductor-based step- down conversion provides the highest efficiency, but the solution cost and circuit complexity are much higher. The LTC1503-X provides the efficiency advantages associated with inductor-based circuits as well as the cost and sim- plicity advantages of an inductorless converter. The LTC1503-X is a switched capacitor step-down DC/DC converter. The part uses an internal switch network and fractional conversion ratios to achieve high efficiency over widely varying VIN and output load conditions. Internal control circuitry selects the appropriate step-down con- version ratio based on VIN, VOUT and load conditions to optimize efficiency. The part has three possible step-down modes: 2-to-1, 3-to-2 or 1-to-1 (gated switch) step-down mode. Only two external flying caps are needed to operate in all three modes. 2-to-1 mode is chosen when VIN is greater than two times the desired VOUT. 3-to-2 mode is chosen when VIN is greater than 1.5 times VOUT but less than 2 times VOUT. 1-to-1 mode is chosen when VIN falls below 1.5 times VOUT. An internal mode skip function will switch the step-down ratio as needed to maintain output regulation under heavy load conditions. Regulation is achieved by sensing the divided down output voltage and enabling the charge pump as needed to boost the output back into regulation. This method of regulation allows the LTC1503-X to achieve high efficiency at very light loads. The part has shutdown capability as well as user controlled inrush current limiting. In addition, the part can withstand an indefinite short-circuit condition on VOUT and is also overtemperature protected. Step-Down Charge Pump Operation Figure 1a shows the charge pump switch configuration that is used for 2-to-1 step down. When the charge pump is enabled in this mode, a two phase nonoverlapping clock generates the switch control signals. On phase one of the clock, flying capacitor C1 is connected through switches Figure 1a. Step-Down Charge Pump in 2-to-1 Mode S1 and S2 across VOUT. If the voltage on C1 is greater than the voltage on COUT, charge is transferred from C1 onto COUT. On phase two, the top plate of C1 is connected to VIN and the bottom plate is connected to VOUT. If the voltage across C1 is less than VIN/2 during phase two, charge will be transferred from C1 onto COUT thereby boosting the voltage on COUT and raising the voltage across C1. Thus, in 2-to-1 mode, charge transfer from C1 onto COUT occurs on both phases of the clock, and the voltage on COUT is driven towards 1/2VIN until the output is back in regula- tion. Since charge current is sourced from ground on phase one of the clock, current multiplication is realized with respect to VIN, i.e., IVOUT equals approximately 2 • IVIN. This results in significant efficiency improvement relative to a linear regulator. The 3-to-2 conversion mode also uses a nonoverlapping clock for switch control but requires two flying capacitors and a total of seven switches (see Figure 1b). On phase one, C1 and C2 are connected in series across VOUT. If the sum of the voltages across C1 and C2 is greater than VOUT, charge is transferred from the flying caps onto COUT thereby reducing the average voltage on the flying caps and raising the voltage on the output capacitor. On phase two, the two flying capacitors are connected on parallel between VIN and VOUT. Since the average voltage across the two capacitors during phase one is VOUT/2, charge will be transferred from VIN to VOUT through the two flying caps if VIN minus VOUT/2 is greater than VOUT. In this manner, charge is again transferred from the flying caps to the output on both phases of the clock, and the voltage on COUT is driven towards (2/3)VIN until the part is back in regulation. As in 2-to-1 mode, charge current is sourced from ground on phase one of the clock which results in increased power efficiency. IVOUT in 3-to-2 mode equals approximately (3/2)IVIN. S4 φ2 S1 φ1 S3 φ2 S2 φ1 C1 (EXTERNAL) C1+ C1– 1503-1.8/2 F01a VIN VOUT APPLICATIO S I FOR ATIO |
Similar Part No. - 15032 |
|
Similar Description - 15032 |
|
|
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 |