Electronic Components Datasheet Search |
|
MIC5190 Datasheet(PDF) 7 Page - Micrel Semiconductor |
|
MIC5190 Datasheet(HTML) 7 Page - Micrel Semiconductor |
7 / 13 page MIC5190 Micrel Applications Information Designing with the MIC5190 Anatomy of a transient response The measure of a regulator is how accurately and effectively it can maintain a set output voltage, regardless of the load's power demands. One measure of regulator response is the load step. The load step gauges how the regulator responds to a change in load current. Figure 2 is a look at the transient response to a load step. Figure 2. Typical Transient Response At the start of a circuit's power demand, the output voltage is regulated to its set point, while the load current runs at a constant rate. For many different reasons, a load may ask for more current without warning. When this happens, the regu- lator needs some time to determine the output voltage drop. This is determined by the speed of the control loop. So, until enough time has elapsed, the control loop is oblivious to the voltage change. The output capacitor must bear the burden of maintaining the output voltage. Since this is a sudden change in voltage, the capacitor will try to maintain voltage by discharging current to the output. The first voltage drop is due to the output capacitor's ESL (equiva- lent series inductance). The ESL will resist a sudden change in current from the capacitor and drop the voltage quickly. The amount of voltage drop during this time will be proportional to the output capacitor's ESL and the speed at which the load steps. Slower load current transients will reduce this effect. Placing multiple small capacitors with low ESL in parallel can help reduce the total ESL and reduce voltage droop during high speed transients. For high speed transients, the greatest voltage deviation will generally be caused by output capacitor ESL and parasitic inductance. After the current has overcome the effects of the ESL, the output voltage will begin to drop proportionally to time and inversely proportional to output capacitance. Output voltage variation will depend on two factors: loop bandwidth and output capacitance. The output capacitance will determine how far the voltage will fall over a given time. With more capacitance, the drop in voltage will fall at a decreased rate. This is the reason that more capacitance provides a better transient response for the same given bandwidth. The time it takes for the regulator to respond is directly proportional to its bandwidth gain. Higher bandwidth control loops respond quicker causing a reduced drop on the supply for the same amount of capacitance. Final recovery back to the regulated voltage is the final phase of transient response and the most important factors are gain and time. Higher gain at higher frequency will get the output voltage closer to its regulation point quicker. The final settling point will be determined by the load regulation, which is proportional to DC (0Hz) gain and the associated loss terms. There are other factors that contribute to large signal tran- sient response, such as source impedance, phase margin, and PSRR. For example, if the input voltage drops due to source impedance during a load transient, this will contribute to the output voltage deviation by filtering through to the output reduced by the loops PSRR at the frequency of the voltage transient. It is straightforward: good input capaci- tance reduces the source impedance at high frequencies. Having between 35 ° and 45° of phase margin will help speed up the recovery time. This is caused by the initial overshoot in response to the loop sensing a low voltage. Compensation The MIC5190 has the ability to externally control gain and bandwidth. This allows the MIC5190 design to be individually tailored for different applications. In designing the MIC5190, it is important to maintain ad- equate phase margin. This is generally achieved by having the gain cross the 0dB point with a single pole 20dB/decade roll-off. The compensation pin is configured as Figure 3 demonstrates. Error Amplifier Driver 3.42M Ω 20pF Internal External Comp Figure 3. Internal Compensation ∆ V L di dt = ∆V C idt =∫ 1 ∆V C idt ↓= ↑ ∫ 1 ∆V C idt ↓= ∫ ↓ 1 ∆V L di dt ↓= ↑ ∆V L di dt ↓= ↓ Time ∫idt C V = 1 BW 1 Output voltage vs. time during recovery is directly proportional to gain vs. frequency. ∆ V = L di dt December 2005 7 M9999-120105 |
Similar Part No. - MIC5190_04 |
|
Similar Description - MIC5190_04 |
|
|
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 |