Electronic Components Datasheet Search |
|
AMS2954AC-50 Datasheet(PDF) 10 Page - Advanced Monolithic Systems |
|
AMS2954AC-50 Datasheet(HTML) 10 Page - Advanced Monolithic Systems |
10 / 15 page Advanced Monolithic Systems, Inc. 6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140 AMS2954 APPLICATION HINTS (Continued) R 1 ERROR* ERROR OUPUT **SHUTDOWN INPUT GND FB V OUT V REF R 2 SD 1.23 V 7 4 3 8 1 5 +V IN +V IN V OUT 1.2 30V 3.3 µF .01µ F + * 100k AMS2954 FIGURE 2. Adjustable Regulator *See Application Hints. Vout = VREF × (1 + R1/ R2) **Drive with TTL- high to shut down. Ground or leave if shutdown feature is not used. Note: Pins 2 and 6 are left open. Reducing Output Noise In reference applications it may be an advantageous to reduce the AC noise present at the output. One method is to reduce the regulator bandwidth by increasing the size of the output capacitor. This is the only way that noise can be reduced on the 3 lead AMS2954 but is relatively inefficient, as increasing the capacitor from 1 µF to 220 µF only decreases the noise from 430 µV to 160 µV rms for a 100 kHz bandwidth at 5V output. Noise could also be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick CBYPASS ≅ 1 / 2πR1 × 200 Hz or about 0.01 µF. When doing this, the output capacitor must be increased to 3.3 µF to maintain stability. These changes reduce the output noise from 430 µV to 100 µV rms for a 100 kHz bandwidth at 5V output. With the bypass capacitor added, noise no longer scales with output voltage so that improvements are more dramatic at higher output voltages. Heatsink Requirements A heatsink might be required when using AMS2954, depending on the maximum power dissipation and maximum ambient temperature of the application. The heatsink must be chosen considering that under all operating condition, the junction temperature must be within the range specified under Absolute Maximum Ratings. To determine if a heatsink is required, the maximum power dissipated by the regulator must be calculated. It is important to consider, that if the regulator is powered from a transformer connected to the AC line, the maximum specified AC input voltage must be used. GND OUT V IN AMS2954 5V 1 µF * IN + LOAD I L I G I IN * See external capacitors P Total = (VIN -5)IL +(VIN)IG I IN = IL +IG FIGURE 3. Basic 5V Regulator Figure 3 shows the voltages and currents which are present in a 5V regulator circuit. The formula for calculating the power dissipated in the regulator is also shown in Figure 3. The next parameter which must be calculated is the maximum allowable temperature rise, TR(max). This is calculated using the formula: TR(max) =TJ(max) - TA(max) Where TJ(max) is the maximum allowable junction temperature, and TA(max) is the maximum ambient temperature. Using the calculated values for TR(max) and P(max), the required value for junction to ambient thermal resistance θ (J-A), can be determined: θ (J-A) = TR(max) /P(max) If the value obtained is 60 °C/W or higher, the regulator may be operated without an external heatsink. If the calculated value is below 60 °C/W, an external heatsink is required. To calculate the thermal resistance of this heatsink use the formula: θ (H-A) = θ(J-A) - θ(J-C) - θ(C-H) where: θ (J-C) is the junction-to-case thermal resistance, which is specified as 3 °C/W maximum for the AMS2954. θ (C-H) is the case-to-heatsink thermal resistance, which is dependent on the interfacing material (if used). θ (H-A) is the heatsink-to-ambient thermal resistance. It is this specification which defines the effectiveness of the heatsink. The heatsink selected must have a thermal resistance equal or lower than the value of θ (H-A) calculated from the above listed formula. Output Isolation The regulator output can be left connected to an active voltage source with the regulator input power turned off, as long as the regulator ground pin is connected to ground. If the ground pin is left floating, damage to the regulator can occur if the output is pulled up by an external voltage source. |
Similar Part No. - AMS2954AC-50 |
|
Similar Description - AMS2954AC-50 |
|
|
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 |