feature

At +25°C, line and load accuracy is ±0.8%, and temperature accuracy is ±1.4%; ultra-low dropout voltage: 180mV (typ) at 200mA , stability requires only CO = 0.47 µF; anyCAP = stable with all types of capacitors (including MLCCs); 3.2 V to 12 V supply range; current and thermal limits; low noise; Thermally enhanced SOIC package; excellent line and load regulation.

application

Cell Phones; Notebook, Handheld Computer Battery-Powered Systems; Portable Instruments; Post-Regulators for Switching Power Barcode Scanners.

General Instructions

The ADP3303 is a member of the ADP330x family of precision low dropout arbitrary capacitor voltage regulators. Unlike traditional LDOs, the ADP3303 has a different architecture, enhanced flow, and a different software package. Its patented design requires only a 0.47µF output capacitor for stable operation. The device is insensitive to capacitor Equivalent Series Resistance (ESR) and is stable with any quality capacitor, including the ceramic type (MLCC) for space-constrained applications. The ADP3303 achieves an exceptional accuracy of ±0.8% at room temperature and an overall accuracy of ±1.4% for temperature, line, and load regulation. The dropout voltage of the ADP3303 is only 180mV (typ) at 200mA.

In addition to the architecture and process, Analog Devices' proprietary thermally enhanced package (Thermal Shoreline) can handle 1W of power dissipation without the need for an external heat sink or large copper surfaces on a printed circuit board (PCB). This minimizes PCB real estate, making the ADP3303 very attractive in portable devices.

The ADP3303 operates over a wide input voltage range of 3.2V to 12V and provides over 200mA of load current.

It has an error flag that signals when the unit is about to lose regulation or when a short circuit or thermal overload protection is activated. Other features include shutdown and optional noise cancellation. The ADP330x anyCAP LDO family offers a wide range of output voltage and output current levels:

Typical performance characteristics

theory of operation

The new anyCAP LDO ADP3303 uses a separate control loop for regulation and reference functions. The output voltage is sensed by a resistive divider consisting of R1 and R2, which can be changed to provide the available output voltage options. Feedback is passed from this network to the input of the amplifier through a series diode (D1) and a second resistive divider (R3 and R4).

A high gain error amplifier is used to control this loop. The amplifier is constructed so that at equilibrium it produces a large, temperature-proportional input bias voltage that is repeatable and well-controlled. The temperature-proportional bias voltage combines with the complementary diode voltage to form a virtual bandgap voltage implicit in the network, although it never appears explicitly in the circuit. Ultimately, this patented design makes it possible to control the loop with just one amplifier. This technique also improves the noise characteristics of amplifiers by providing greater flexibility in the trade-offs of noise sources that lead to low-noise designs.

The choice of the R1, R2 voltage divider is the same as the ratio of the bandgap voltage to the output voltage. Although the R1, R2 resistor divider is loaded by diode D1 and a second divider consisting of R3 and R4, these values are chosen to produce a temperature stable output. This unique arrangement specifically corrects the load of the divider to avoid errors due to base current loading in conventional circuits.

A patented amplifier controls a new and unique non-rotating driver, driven through transistor, Q1. Using this special non-vertical driver, frequency compensation is able to include the load capacitor in the polar arrangement to reduce sensitivity to the value, type and ESR of the load capacitor.

Due to the uncertainty of the load capacitance and resistance, most LDOs impose strict requirements on the range of the ESR value of the output capacitor. Furthermore, the ESR value required to keep a conventional ldo stable varies with load and temperature. These ESR limitations make the design of ldos more difficult because ldos are poorly specified and subject to extreme changes with temperature.

Not so with the ADP3303 anyCAP LDO. The ADP3303 can be used with almost any capacitor and there is no limit to the minimum ESR. The innovative design makes the circuit stable with only a small 0.47μF capacitor at the output. Other advantages of the pole-splitting scheme include superior line noise rejection and very high regulator gain, which results in good line and load regulation. An impressive ±1.4% accuracy is guaranteed over line, load and temperature.

Other features of this circuit include current limit, thermal shutdown, and noise reduction. Compared to standard solutions that warn when the output is out of regulation, the ADP3303 provides improved system performance by enabling the ERR pin to warn before the device is out of regulation.

When the die temperature rises above 165°C, the circuit initiates a soft thermal shutdown, indicated by a low signal on the ERR pin, to reduce the current to a safe level. To reduce the noise gain of the loop, the node of the main divider network (a) is provided at the noise reduction (NR) pin, which can be bypassed by a small capacitor (10nf to 100nf).

application information

Capacitor selection

output capacitor

As with any micropower device, the output transient response is a function of the output capacitance. The ADP3303 has stable capacitance values, types, and ESR ranges. Capacitors as low as 0.47µF are all that is needed for stabilization; larger capacitors can be used if high output current surges are expected. The ADP3303 is a stable very low ESR capacitor (ESR ≈ 0) such as multilayer ceramic capacitors (MLCCs) or OSCONs.

Input Bypass Capacitor

No input bypass capacitors are required. For applications where the input source is high impedance or away from the input pins, use a bypass capacitor. Connecting a 0.47µF capacitor from the input pin to ground reduces the circuit's sensitivity to PCB layout. If larger value output capacitors are used, larger value input capacitors are also recommended.

Noise reduction

Noise can be further reduced by 6dB to 10dB using a noise reduction capacitor (CNR) (see Figure 23). Low leakage capacitors in the 10nF to 100nF range provide the best performance. Since the noise reduction pin (NR) is internally connected to a high impedance node, care must be taken to connect to this node to avoid receiving noise from external sources. The pad connected to this pin must be as small as possible. Long PCB traces are not recommended.

Thermal overload protection

The ADP3303 is protected from damage due to the excessive power dissipation of the thermal overload protection circuit, limiting the die temperature to below 165°C under extreme conditions (i.e. high ambient temperature and power dissipation), where the die temperature begins to rise to 165°C Above °C, the output current is reduced until the mold temperature drops to a safe level. When the mold temperature decreases, the output current resumes.

Current and thermal limit protection is designed to protect the unit from accidental overload conditions. For normal operation, device power dissipation must be limited externally so that the junction temperature does not exceed 125°C.

Calculate the junction temperature

The power consumption of the device is calculated as follows:

Where: ILOAD and IGND are the load current and ground current. VIN and VOUT are the input and output voltages, respectively. Assuming ILOAD=200mA, IGND=2mA, VIN=7V, VOUT=5.0V, the power consumption of the device is:

The proprietary software package used in the ADP3303 has a resistance of 96°C/W, significantly lower than the standard 8-lead solid package at 170°C/W.

Junction temperature above ambient is approximately equal to:

To limit the maximum junction temperature to 125°C, the maximum ambient temperature must be below:

PCB Layout Considerations

All surface mount packages rely on PCB traces to carry heat away from the package.

In a standard package, the main component of the thermal path is the plastic between the die attach pads and the individual leads. In a typical thermally enhanced package, one or more leads are fused to the die attach pads, significantly reducing this assembly. However, for the improvement to be meaningful, important copper areas on the PCB must be connected to these fuse pins.

The patented thermal shoreline leadframe design of the ADP3303 (see Figure 24) uniformly minimizes the value of a major portion of thermal resistance. It ensures that the heat is carried away by all the pins on the package. This results in a very low thermal resistance of 96°C/W for the SOIC package, which does not require any special board layout requirements, relying on normal traces connected to the leads. The thermal resistance can be reduced by about 10% by adding a few square centimeters of copper area to the IN pin of the ADP3303. Do not use solder masks or silkscreens on the PCB traces near the ADP3303 pins, as this will increase the junction-to-ambient thermal resistance of the package.

Error Flag Loss Detector

The ADP3303 maintains its output voltage at load, input voltage, and temperature conditions. For example, the ERR flag activates if, for example, the output will run out of control by reducing the supply voltage below the combined regulated output and dropout voltage. The error output is an open collector, driven low.

Once set, the hysteresis of the ERR flag keeps the output low until a small fraction of the operating range is achieved by raising the supply voltage or lowering the load.

shutdown mode

Apply a TTL high signal to the shutdown (SD) pin, or tie it to an input pin, to turn on the output. Drop SD to 0.3 V either below, or tie it to ground to turn off the output. In shutdown mode, the quiescent current is reduced to much less than 1 µA.

application circuit

crossbar switch

The circuit in Figure 25 shows that two ADP3303s can be used to form a mixed supply voltage system. The output switches between two different levels selected by an external digital input. The output voltage can be any combination of voltages in the ordering guide.

high output current

The ADP3303 can supply up to 200 mA without any heat sink or transistor. If higher current is required, an appropriate transistor can be used, as shown in Figure 26, to increase the output current to 1A.

Constant differential pressure regulator

The circuit in Figure 27 provides high accuracy and low losses for any regulated output voltage. It significantly reduces switching regulator ripple while providing a constant voltage drop, limiting the LDO's power dissipation to 60mW. The ADP3000 used in this circuit is a switching regulator in a boost configuration.

Dimensions