Electronic Components Datasheet Search |
|
LTC1754-5 Datasheet(PDF) 7 Page - Linear Technology |
|
LTC1754-5 Datasheet(HTML) 7 Page - Linear Technology |
7 / 12 page 7 LTC1754-3.3/LTC1754-5 range. The capacitor manufacturer’s data sheet should be consulted to determine what style and value of capacitor is needed to ensure 0.6 µF at all temperatures. Output Ripple Low frequency regulation mode ripple exists due to the hysteresis in the sense comparator and propagation delay in the charge pump control circuit. The amplitude and frequency of this ripple are heavily dependent on the load current, the input voltage and the output capacitor size. For large VIN the ripple voltage can become substantial because the increased strength of the charge pump causes fast edges that may outpace the regulation circuitry. Generally the regulation ripple has a sawtooth shape associated with it. A high frequency ripple component may also be present on the output capacitor due to the charge transfer action of the charge pump. In this case the output can display a voltage pulse during the charging phase. This pulse results from the product of the charging current and the ESR of the output capacitor. It is proportional to the input voltage, the value of the flying capacitor and the ESR of the output capacitor. Typical combined output ripple for the LTC1754-5 with VIN = 3V under maximum load is 65mVP-P using a low ESR 10 µF output capacitor. A smaller output capacitor and/or larger output current load will result in higher ripple due to higher output voltage slew rates. There are several ways to reduce output voltage ripple. For applications requiring higher VIN or lower peak-to-peak ripple, a larger COUT capacitor (22µF or greater) is recom- mended. A larger capacitor will reduce both the low and high frequency ripple due to the lower charging and discharging slew rates, as well as the lower ESR typically found with higher value (larger case size) capacitors. A low ESR ceramic output capacitor will minimize the high frequency ripple, but will not reduce the low frequency ripple unless a high capacitance value is used. To reduce both the low and high frequency ripple, a reasonable compromise is to use a 10 µF to 22µF tantalum capacitor in parallel with a 1 µF to 3.3µF ceramic capacitor on VOUT. An R-C filter may also be used to reduce high frequency voltage spikes (see Figure 1). Figure 1. Output Ripple Reduction Techniques In low load or high VIN applications, smaller values for the flying capacitor may be used to reduce output ripple. A smaller flying capacitor (0.01 µF to 0.47µF) delivers less charge per clock cycle to the output capacitor resulting in lower output ripple. However, with a smaller flying capaci- tor, the maximum available output current will be reduced along with the efficiency. Note that when using a larger output capacitor the turn on time of the device will increase. Inrush Currents During normal operation VIN will experience current tran- sients in the 50mA to 100mA range whenever the charge pump is enabled. However during start-up, inrush cur- rents may approach 250mA. For this reason it is important to minimize the source impedance between the input supply and the VIN pin. Too much source impedance may result in regulation problems or prevent start-up. Ultralow Quiescent Current Regulated Supply The LTC1754 contains an internal resistor divider (refer to the Simplified Block Diagram) that typically draws 1.5 µA from VOUT. During no-load conditions, this internal load causes a droop rate of only 150mV per second on VOUT with COUT = 10µF. Applying a 2Hz to 100Hz, 2% to 5% duty cycle signal to the SHDN pin ensures that the circuit of Figure 2 comes out of shutdown frequently enough to maintain regulation. Since the LTC1754 spends nearly the entire time in shutdown, the no-load quiescent current is approximately (VOUT)(1.5µA)/(ηVIN). The LTC1754 must be out of shutdown for a minimum duration of 200 µstoallowenoughtimetosensetheoutput voltage and keep it in regulation. A 2Hz, 2% duty cycle LTC1754-X 15 µF TANTALUM VOUT VOUT VOUT 1 µF CERAMIC LTC1754-X 2 Ω 10 µF TANTALUM 10 µF TANTALUM VOUT 1754 F01 + + + APPLICATIO S I FOR ATIO |
Similar Part No. - LTC1754-5_15 |
|
Similar Description - LTC1754-5_15 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | 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 |