Electronic Components Datasheet Search |
|
LMC7211AIM5 Datasheet(PDF) 11 Page - Texas Instruments |
|
|
LMC7211AIM5 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 23 page LMC7211-N www.ti.com SNOS746F – MAY 2004 – REVISED JANUARY 2013 Figure 5. Measurement of the Shoot-Through Current From Figure 5, the shoot-through current for the LMC7211 can be calculated to be 0.2 mA (typical), and the duration is 1 μs. The values needed for the bypass capacitors can be calculated as follows: Area of Δ = ½ (1 μs × 200 μA) = 100 pC The capacitor needs to supply 100 picocolumb. To avoid large shifts in the comparator threshold due to changes in the voltage level, the voltage drop at the bypass capacitor should be limited to 100 mV or less. The charge needed (100 picocolumb) and the allowable voltage drop (100 mV) will give us the minimum capacitor value required. ΔQ = C ( ΔV) C = ΔQ/ΔV = 100 picocolumb/100 mV C = 10-10/10-1 = 10-9 = 1 nF = 0.001 μF 10-9 = 1 nF = 0.001 μF The voltage drop of ∼100 mV will cause a threshold shift in the comparator. This threshold shift will be reduced by the power supply rejection ratio, (PSRR). The PSRR which is applicable here is not the DC value of PSRR ( ∼80 dB), but a transient PSRR which will be usually about 20 dB–40 dB, depending on the circuit and the speed of the transient. This will result in an effective threshold shift of about 1 mV to 10 mV. For precision and level sensing circuits, it is generally a good goal to reduce the voltage delta on the power supply to a value equal to or less than the hysteresis of the comparator circuit. If the above circuit was to be used with 50 mV of hysteresis, it would be reasonable to increase the bypass capacitor to 0.01 μF to reduce the voltage delta to 10 mV. Larger values may be useful for obtaining more accurate and consistent switching. Note that the switching current of the comparator can spread to other parts of the board as noise. The bypass capacitor reduces this noise. For low noise systems this may be reason to make the capacitor larger. For non-precision circuits, such as using a comparator to determine if a push-button switch is on or off, it is often cheaper and easier to use a larger value of hysteresis and a small value or bypass capacitance. The low shoot- through current of the LMC7211 can allow the use of smaller and less expensive bypass capacitors in non-critical circuits. Copyright © 2004–2013, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Links: LMC7211-N |
Similar Part No. - LMC7211AIM5 |
|
Similar Description - LMC7211AIM5 |
|
|
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 |