ADP3330

Data Sheet

CALCULATING JUNCTION TEMPERATURE

Device power dissipation is calculated as follows:

PD = (VIN − VOUT) ILOAD + (VIN) IGND

where:

ILOAD and IGND are load current and ground current.

VIN and VOUT are input and output voltages, respectively.

Assuming ILOAD = 200 mA, IGND = 4 mA, VIN = 4.2 V, and VOUT =

3.0 V, the device power dissipation is the following:

PD = (4.2 − 3.0) 200 mA + 4.2 (4 mA) = 257 mW

The proprietary package used in the ADP3330 has a thermal

resistance of 165°C/W, significantly lower than the standard

6-lead SOT-23 package. Assuming a 4-layer board, the junction

temperature rise above ambient temperature is approximately

equal to

ΔTJA = 0.257 W × 165°C/W = 42.4°C

To limit the maximum junction temperature to 125°C,

maximum allowable ambient temperature is

TA MAX = 125°C − 42.4°C = 82.6°C

PRINTED CIRCUIT BOARD (PCB) LAYOUT

CONSIDERATIONS

All packages rely on the traces of the PCB 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. To make the improvement

meaningful, however, a significant copper area on the PCB must

be attached to these fused pins.

The patented chip-on-lead frame design of the ADP3330

uniformly minimizes the value of the dominant portion of the

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

of the package pins and yields a very low 165°C/W thermal

resistance for the 6-lead SOT-23 package. Low thermal

resistance is achieved without any special board layout

requirements, just the normal traces connected to the leads, and

yields a 17% improvement in heat dissipation capability as

compared to a standard 6-lead SOT-23 package. The thermal

resistance can be decreased by approximately an additional 10%

by attaching a few square cm of copper area to the VIN pin of the

ADP3330 package.

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

PCB traces adjacent to the pins of the ADP3330 because it

increases the junction to ambient thermal resistance of the

package.

ERROR FLAG DROPOUT DETECTOR

The ADP3330 maintains its output voltage over a wide range of

load, input voltage, and temperature conditions. If the output is

about to lose regulation by reducing the supply voltage less than

the combined regulated output and dropout voltages, the ERR

flag is activated. The ERR output is an open collector that is

driven low.

When the ERR output is set, the hysteresis of the ERR flag keeps

the output low until a small margin of the operating range is

restored either by raising the supply voltage or reducing the load.

SHUTDOWN MODE

Applying a TTL high signal to the shutdown (SD) pin, or tying

the SD pin to the input pin, turns the output on. Pulling the SD

pin down to 0.4 V or below, or tying the SD pin to ground,

turns the output off (we do not do all caps for emphasis). In

shutdown mode, the ground current is reduced to much less

than 1 µA.

LOW POWER, LOW DROPOUT APPLICATIONS

The ADP3330 is well suited for applications such as cell phone

handsets that require low ground current and low dropout

voltage features. The ADP3330 typically draws 34 µA under

light load situations (that is, load current = 100 µA), which

results in low power consumption when the cell phone is in

standby mode.

Figure 26 shows an application in which the ADP3330 is used

in a handset to provide 2.75 V nominal output voltage. The cell

phone is powered from a 3 cell NiCd or 1 cell Li-Ion battery.

The ADP3330 guarantees an accuracy of 1.4%, even when the

input/output differential is merely 250 mV (worst case).

Therefore, the voltage output is regulated and within

specification even when the battery voltage has reached its end

of discharge voltage of 3 V. The output voltage never falls less

than 2.7 V, even under worst case load and temperature

conditions. The low dropout feature coupled with the high

accuracy of the ADP3330 ensures that the system is reliably

powered until the end of the life of the battery, which results in

increased system talk time.

Figure 26. LDO Budgeting for a 3 Cell NiCd/1 Cell Li-Ion Supply

MINIMUM BATTERY

VOLTAGE 3.0V

NOMINAL OUTPUT

VOLTAGE 2.75V

2.712V

ABSOLUTE MINIMUM

OUTPUT VOLTAGE

2.700V

END OF DISCHARGE VOLTAGE

OF 3 CELL NiCd OR 1 CELL

Li-Ion BATTERY

250mV MAXIMUM INPUT-OUTPUT

OVERHEAD FOR 200mA OUTPUT

CURRENT

–1.4% OUTPUT

VOLTAGE ACCURACY

12mV TRANSIENT, LINE AND

LOAD RESPECTIVE MARGIN

Rev. C | Page 12 of 16