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ADP3302

APPLICATION INFORMATION

anyCAP

™

The ADP3302 is an easy to use dual low dropout voltage

regulator. The ADP3302 requires only a very small 0.47

µF bypass

capacitor on the outputs for stability. Unlike the conventional

LDO designs, the ADP3302 is stable with virtually any type of

capacitors (anyCAP™) independent of the capacitor’s ESR

(Effective Series Resistance) value.

Capacitor Selection

Output Capacitors: As with any micropower device, output

transient response is a function of the output capacitance. The

ADP3302 is stable with a wide range of capacitor values, types

and ESR (anyCAP™). A capacitor as low as 0.47 F is all that

is needed for stability. However, larger capacitors can be used if

high output current surges are anticipated. The ADP3302 is

stable with extremely low ESR capacitors (ESR

≈ 0), such as

multilayer ceramic capacitors (MLCC) or OSCON.

Input Bypass Capacitor: An input bypass capacitor is not

required. However, for applications where the input source is

high impedance or far from the input pins, a bypass capacitor is

recommended. Connecting a 0.47 F capacitor from the input

pins (Pins 5 and 8) to ground reduces the circuit’s sensitivity to

PC board layout.

Low ESR capacitors offer better performance on a noisy supply;

however, for less demanding requirements a standard tantalum

or aluminum electrolytic capacitor is adequate.

Thermal Overload Protection

The ADP3302 is protected against damage due to excessive

power dissipation by its thermal overload protection circuit,

which limits the die temperature to a maximum of 165

°C.

Under extreme conditions (i.e., high ambient temperature and

power dissipation) where die temperature starts to rise above

165

°C, the output current is reduced until the die temperature

has dropped to a safe level. The output current is restored when

the die temperature is reduced.

Current and thermal limit protections are intended to protect

the device against accidental overload conditions. For normal

operation, device power dissipation should be externally limited

so that junction temperatures will not exceed 125

°C.

Calculating Junction Temperature

Device power dissipation is calculated as follows:

voltages respectively.

PD = (7.2 V – 5 V) 100 mA + (7.2 V – 5 V) 100 mA + (7.2 V)

2 mA = 0.454 W

The proprietary thermal coastline lead frame used in the

ADP3302 yields a thermal resistance of 96

°C/W, which is signi-

ficantly lower than a standard 8-pin SOIC package at 170

°C/W.

Junction temperature above ambient temperature will be

approximately equal to:

0.454 W

96

°C/W = 43.6°C

To limit the maximum junction temperature to 125

°C, maxi-

mum ambient temperature must be lower than:

43.6

°C = 81.4°C

PRINTED CIRCUIT BOARD LAYOUT CONSIDERATION

All surface mount packages rely on the traces of the PC board to

conduct heat away from the package.

In standard packages the dominant component of the heat

resistance path is the plastic between the die attach pad and the

individual leads. In typical thermally enhanced packages one or

more of the leads are fused to the die attach pad, significantly

decreasing this component. However, to make the improvement

meaningful, a significant copper area on the PCB has to be

attached to these fused pins.

The ADP3302’s patented thermal coastline lead frame design

uniformly minimizes the value of the dominant portion of the

thermal resistance. It ensures that heat is conducted away by all

pins of the package. This yields a very low 96

°C/W thermal

resistance for an SO-8 package, without any special board lay-

out requirements, relying just on the normal traces connected to

the leads. The thermal resistance can be decreased by, approxi-

mately, an additional 10% by attaching a few square cm of

It is not recommended to use solder mask or silkscreen on the

PCB traces adjacent to the ADP3302 pins since it will increase

the junction to ambient thermal resistance of the package.

Shutdown Mode

Applying a TTL high signal to the shutdown pin or tying it to

the input pin will turn the output ON. Pulling the shutdown pin

down to a TTL low signal or tying it to ground will turn the

output OFF. Outputs are independently controlled. In shutdown

mode, quiescent current is reduced to less than 2 A.

Error Flag Dropout Detector

The ADP3302 will maintain its output voltage over a wide

range of load, input voltage and temperature conditions. If

regulation is lost, for example, by reducing the supply voltage

below the combined regulated output and dropout voltages, the

ERRor flag will be activated. The ERR output is an open

collector, which will be driven low.

Once set, the ERRor flag’s hysteresis will keep the output low

until a small margin of operating range is restored, either by

raising the supply voltage or reducing the load.

A single ERR pin serves both regulators in the ADP3302 and

indicates that one or both regulators are on the verge of losing

regulation.

APPLICATION CIRCUIT

Dual Post Regulator Circuit for Switching Regulators

The ADP3302 can be used to implement a dual 3 V/100 mA

post regulator power supply from a 1 cell Li-Ion input (Figure

20). This circuit takes 2.5 V to 4.2 V as the input and delivers

dual 3 V/100 mA outputs. Figure 21 shows the typical efficiency

curve.

For ease of explanation, let’s partition the circuit into the

ADP3000 step-up regulator section and the ADP3302 low

dropout regulation section. Furthermore, let’s divide the operation

of this application circuit into the following three phases.