Electronic Components Datasheet Search |
|
ADP3331 Datasheet(PDF) 6 Page - Analog Devices |
|
ADP3331 Datasheet(HTML) 6 Page - Analog Devices |
6 / 9 page REV. ADP3331 –6– THEORY OF OPERATION The ADP3331 anyCAP LDO uses a single control loop for both regulation and reference functions, as shown in Figure 2. The output voltage is sensed by an external resistive voltage divider consisting of R1 and R2. Feedback is taken from this network by way of a series diode (D1) and a second resistor divider (R3 and R4) to the input of an amplifier. PTAT VOS gm NONINVERTING WIDEBAND DRIVER INPUT Q1 ADP3331 COMPENSATION CAPACITOR ATTENUATION (VBANDGAP/VOUT) R1 D1 R2 R3 R4 OUTPUT PTAT CURRENT RLOAD CLOAD (a) GND Figure 2. Functional Block Diagram A very high gain error amplifier is used to control this loop. The amplifier is constructed in such a way that at equilibrium it produces a large, temperature-proportional input offset voltage that is repeatable and very well controlled. The temperature- proportional offset voltage is combined with the complementary diode voltage to form a virtual band gap voltage, implicit in the network, although it never appears explicitly in the circuit. Ulti- mately, this patented design makes it possible to control the loop with only one amplifier. This technique also improves the noise characteristics of the amplifier by providing more flexibility on the trade-off of noise sources, which leads to a low noise design. The R1, R2 divider is chosen in the same ratio as the band gap voltage to output voltage. Although the R1, R2 resistor divider is loaded by the diode D1 and a second divider consisting of R3 and R4, the values are chosen to produce a temperature stable output. This unique arrangement specifically corrects for the loading of the divider so that the error resulting from the base current loading in conventional circuits is avoided. The patented amplifier controls a new and unique noninverting driver that drives the pass transistor, Q1. The use of this special noninverting driver enables the frequency compensation to include the load capacitor in a pole-splitting arrangement to achieve reduced sensitivity to the value, type, and ESR of the load capacitor. Most LDOs place strict requirements on the range of ESR values for the output capacitor because they are difficult to stabilize due to the uncertainty of the load capacitance and resistance. More- over, the ESR value required to keep conventional LDOs stable changes, depending on load and temperature. These ESR limita- tions make designing with LDOs more difficult because of their unclear specifications and extreme variations over temperature. The ADP3331 solves this problem. It can be used with any good quality capacitor, with no constraint on the minimum ESR. The innovative design allows the circuit to be stable with just a small 0.47 mF capacitor on the output. Additional advantages of the pole-splitting scheme include superior line noise rejection and very high regulator gain. The high gain leads to excellent regula- tion, and ±1.4% accuracy is guaranteed over line, load, and temperature. Additional features of the circuit include current limit, thermal shutdown, and an error flag. Compared to standard solutions that give a warning after the output has lost regulation, the ADP3331 provides improved system performance by enabling the ERR pin to give a warning just before the device loses regulation. As the chip’s temperature rises above +165 ∞C, the circuit acti- vates a soft thermal shutdown to reduce the current to a safe level. The thermal shutdown condition is indicated by the ERR signal going low. APPLICATION INFORMATION Capacitor Selection Output Capacitor: The stability and transient response of the LDO is a function of the output capacitor. The ADP3331 is stable with a wide range of capacitor values, types, and ESR (anyCAP). A capacitor as low as 0.47 mF is all that is needed for stability; larger capacitors can be used if high current surges on the output are anticipated. The ADP3331 is stable with extremely low ESR capacitors (ESR ª 0), such as multilayer ceramic capacitors (MLCC) or OSCON. Note that the effective capacitance of some capacitor types falls below the minimum over temperature or with dc voltage. Input Capacitor: An input bypass capacitor is not strictly required but is recommended in any application involving long input wires or high source impedance. Connecting a 0.47 mF capacitor from the input to ground reduces the circuit’s sensitivity to PC board layout and input transients. If a larger output capacitor is necessary, a larger value input capacitor is also recommended. Noise Reduction Capacitor: A noise reduction capacitor can be used to reduce the output noise by 6 dB to 10 dB. This capaci- tor limits the noise gain when connected between the feedback pin (FB) and the output pin (OUT), as shown in Figure 3. Low leakage capacitors in the 10 pF to 500 pF range provide the best performance. Since FB is internally connected to a high imped- ance node, any connection to this node should be carefully done to avoid noise pickup from external sources. The pad connected to this pin should be as small as possible; long PC board traces are not recommended. When adding a noise reduction capacitor, use the following guidelines: ∑ Maintain a minimum load current of 1 mA when not in shutdown. ∑ For CNR values greater than 500 pF, add a 100 kW series resistor (RNR). It is important to note that as CNR increases, the turn-on time will be delayed. With CNR values greater than 1 nF, this delay may be on the order of several milliseconds. B |
Similar Part No. - ADP3331_15 |
|
Similar Description - ADP3331_15 |
|
|
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 |