ADP3367

–6–

REV. 0

+

C1

10µF

IN

OUT

LBO

ADP3367

+5V

OUTPUT

R2

10k

Ω

LBI

GND

SET

SHDN

DROPOUT

STATUS

OUTPUT

DD

R1

100k

Ω

+

Figure 11. Dropout Status Output

Output Capacitor

An output capacitor is required on the ADP3367 to maintain sta-

bility and also to improve the load transient response. Capacitor

values from 10

µF upwards are recommended. Capacitors larger

than 10

µF will further improve the transient response. Tantalum

or aluminum electrolytics are suitable for most applications. For

temperatures below about –25

°C, solid tantalums should be used

as many aluminum electrolytes freeze at this temperature.

Quiescent Current Considerations

The ADP3367 uses a PNP output stage to achieve low dropout

voltages combined with high output current capability. Under

normal regulating conditions the quiescent current is extremely

low. However if the input voltage drops so that it is below the

desired output voltage, the quiescent current increases consider-

ably. This happens because regulation can no longer be main-

tained and large base current flows in the PNP output transistor

in an attempt to hold it fully on. For minimum quiescent cur-

rent, it is therefore important that the input voltage is main-

tained higher than the desired output level. If the device is being

powered using a battery that can discharge down below the rec-

ommended level, there are a couple of techniques that can be

applied to reduce the quiescent current, but at the expense of

dropout voltage. The first of these is illustrated in Figure 12. By

connecting DD to SHDN the regulator is partially disabled with

input voltages below the desired output voltage and therefore

the quiescent current is reduced considerably.

+

C1

10µF

IN

OUT

ADP3367

+5V

OUTPUT

GND

SET

SHDN

DD

R1

47k

Ω

+

C2

0.1µF

Figure 12. IQ Reduction 1

Another technique for reducing the quiescent current near drop-

out is illustrated in Figure 13. The DD output is used to modify

age setpoint also drops. This technique only works when exter-

reached, the DD output starts sourcing current into the SET

input through R3. This increases the SET voltage so that the

regulator feedback loop does not drive the internal PNP transis-

tor as hard as it otherwise would. As the input voltage continues

to decrease, more current is sourced, thereby reducing the PNP

drive even further. The advantage of this scheme is that it main-

which point the batteries are well outside their useful operating

range. The output voltage tracks the input voltage minus the

dropout. The SHDN function is also unaffected and may be

used normally if desired.

+

C1

10µF

IN

OUT

ADP3367

+5V

OUTPUT

GND

SET

SHDN

DD

R1

610k

Ω

R2

2M

Ω

R3

1M

Ω

+

QUIESCENT CURRENT BELOW DROPOUT

0

16

23

5

400

200

900

1mA

800

700

600

500µA

300

100

4

1.2mA

900µA

Figure 13. IQ Reduction 2

POWER DISSIPATION

The ADP3367 can supply currents up to 300 mA and can oper-

ate with input voltages as high as 16.5 V, but not simultaneously.

It is important that the power dissipation and hence the internal

die temperature be maintained below the maximum limits. Power

Dissipation is the product of the voltage differential across the

regulator times the current being supplied to the load. The

maximum package power dissipation is given in the Absolute

Maximum Ratings. In order to avoid excessive die temperatures,

these ratings must be strictly observed.

The die temperature is dependent on both the ambient tempera-

ture and on the power being dissipated by the device. The inter-

nal die temperature must not exceed 125

°C. Therefore, care

must be taken to ensure that, under normal operating condi-

tions, the die temperature is kept below the thermal limit.

θ