 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LTC3548-2 Datasheet(PDF) 10 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LTC3548-2 Datasheet(HTML) 10 Page - Linear Technology |
|
|
10 / 16 page  LTC3548-2 10 35482fa ceramic capacitors should be used. A good selection of ceramic capacitors is available from Taiyo Yuden, AVX, Kemet, TDK, and Murata. Great care must be taken when using only ceramic input and output capacitors. When a ceramic capacitor is used at the input and the power is being supplied through long wires, such as from a wall adapter, a load step at the output can induce ringing at the VIN pin. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, the ringing at the input can be large enough to damage the part. Since the ESR of a ceramic capacitor is so low, the input and output capacitor must instead fulfill a charge storage requirement. During a load step, the output capacitor must instantaneously supply the current to support the load until the feedback loop raises the switch current enough to support the load. The time required for the feedback loop to respond is dependent on the compensation and the output capacitor size. Typically, 3-4 cycles are required to respond to a load step, but only in the first cycle does the output drop linearly. The output droop, VDROOP, is usually about 2-3 times the linear drop of the first cycle. Thus, a good place to start is with the output capacitor size of approximately: C I fV OUT OUT O DROOP ≈ ∆ 25 . • More capacitance may be required depending on the duty cycle and load step requirements. In most applications, the input capacitor is merely re- quired to supply high frequency bypassing, since the impedance to the supply is very low. A 10 µF ceramic capacitor is usually enough for these conditions. Setting the Output Voltage for Channel 2 The LTC3548-2 develops a 0.6V reference voltage be- tween the feedback pin, VFB2, and the ground as shown in Figure 2. The output voltage, VOUT2, is set by a resistive divider according to the following formula: VV R R OUT2 06 1 2 1 =+ ⎛ ⎝⎜ ⎞ ⎠⎟ . APPLICATIO S I FOR ATIO Keeping the current small (<5 µA) in these resistors maxi- mizes efficiency, but making them too small may allow stray capacitance to cause noise problems and reduce the phase margin of the error amp loop. To improve the frequency response, a feed-forward ca- pacitor CF may also be used. Great care should be taken to route the VOUT1, VFB2 line away from noise sources, such as the inductor or the SW line. Power-On Reset The POR pin is an open-drain output which pulls low when either regulator is out of regulation. When both output voltages are above –8.5% of regulation, a timer is started which releases POR after 218 clock cycles (about 117ms in pulse skip mode). This delay can be significantly longer in Burst Mode operation with low load currents, since the clock cycles only occur during a burst and there could be milliseconds of time between bursts. This can be by- passed by tying the POR output to the MODE/SYNC input, to force pulse skipping mode during a reset. In addition, if the output voltage faults during Burst Mode sleep, POR could have a slight delay for an undervoltage output condition. This can be avoided by using pulse skipping mode instead. When either channel is shut down, the POR output is pulled low, since one or both of the channels are not in regulation. Mode Selection and Frequency Synchronization The MODE/SYNC pin is a multipurpose pin which provides mode selection and frequency synchronization. Connect- ing this pin to VIN enables Burst Mode operation, which provides the best low current efficiency at the cost of a higher output voltage ripple. Connecting this pin to ground selects pulse skipping mode, which provides the lowest output ripple, at the cost of low current efficiency. The LTC3548-2 can also be synchronized to an external 2.25MHz clock signal by the MODE/SYNC pin. During synchronization, the mode is set to pulse skipping and the top switch turn-on is synchronized to the rising edge of the external clock. |
Similar Part No. - LTC3548-2 |
|
Similar Description - LTC3548-2 |
|
|
|
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 |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
