Electronic Components Datasheet Search |
|
AAT1121 Datasheet(PDF) 11 Page - Skyworks Solutions Inc. |
|
AAT1121 Datasheet(HTML) 11 Page - Skyworks Solutions Inc. |
11 / 19 page AAT1121 1.5MHz, 250mA Step-Down Converter DATA SHEET 11 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com 201974B • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • March 15, 2013 Output Voltage (V) L1 (μH) 1.0 1.5 1.2 2.2 1.5 2.7 1.8 3.0 2.5 3.9 3.0 4.7 3.3 5.6 Table 1: Inductor Values. The 3.0μH CDRH2D09 series inductor selected from Sumida has a 150m DCR and a 470mA DC current rat- ing. At full load, the inductor DC loss is 9.375mW which gives a 2.08% loss in efficiency for a 250mA, 1.8V out- put. Input Capacitor Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for CIN. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage. ⎛⎞ · 1 - ⎝⎠ VO VIN CIN = VO VIN ⎛⎞ - ESR · FS ⎝⎠ VPP IO ⎛⎞ · 1 - = for VIN = 2 × VO ⎝⎠ VO VIN VO VIN 1 4 CIN(MIN) = 1 ⎛⎞ - ESR · 4 · FS ⎝⎠ VPP IO Always examine the ceramic capacitor DC voltage coef- ficient characteristics when selecting the proper value. For example, the capacitance of a 10μF, 6.3V, X5R ceram- ic capacitor with 5.0V DC applied is actually about 6μF. The maximum input capacitor RMS current is: ⎛⎞ IRMS = IO · · 1 - ⎝⎠ VO VIN VO VIN The input capacitor RMS ripple current varies with the input and output voltage and will always be less than or equal to half of the total DC load current. ⎛⎞ · 1 - = D · (1 - D) = 0.52 = ⎝⎠ VO VIN VO VIN 1 2 for VIN = 2 x VO IO RMS(MAX) I 2 = The term ⎛⎞ · 1 - ⎝⎠ VO VIN VO VIN appears in both the input voltage ripple and input capacitor RMS current equations and is a maximum when VO is twice VIN. This is why the input voltage ripple and the input capacitor RMS current ripple are a maximum at 50% duty cycle. The input capacitor provides a low impedance loop for the edges of pulsed current drawn by the AAT1121. Low ESR/ESL X7R and X5R ceramic capacitors are ideal for this function. To minimize stray inductance, the capacitor should be placed as closely as possible to the IC. This keeps the high frequency content of the input current localized, minimizing EMI and input voltage ripple. The proper placement of the input capacitor (C1) can be seen in the evaluation board layout in Figure 2. A laboratory test set-up typically consists of two long wires running from the bench power supply to the evalu- ation board input voltage pins. The inductance of these wires, along with the low-ESR ceramic input capacitor, can create a high Q network that may affect converter performance. This problem often becomes apparent in the form of excessive ringing in the output voltage dur- ing load transients. Errors in the loop phase and gain measurements can also result. Since the inductance of a short PCB trace feeding the input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. In applications where the input power source lead induc- tance cannot be reduced to a level that does not affect the converter performance, a high ESR tantalum or alu- minum electrolytic should be placed in parallel with the low ESR, ESL bypass ceramic. This dampens the high Q network and stabilizes the system. |
Similar Part No. - AAT1121 |
|
Similar Description - AAT1121 |
|
|
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 |