ADM663A/ADM666A

REV. 0

–5–

the current drain to a low quiescent (9

µA maximum) current.

This is very useful for low power applications. The SHDN input

should be driven with a CMOS logic level signal since the input

threshold is 0.3 V. In TTL systems, an open collector driver

with a pull-up resistor may be used.

If the shutdown function is not being used, then it should be

connected to GND.

Low Supply or Low Battery Detection

The ADM666A contains on-chip circuitry for low power supply

or battery detection. If the voltage on the LBI pin falls below the

internal 1.3 V reference, then the open drain output LBO will

go low. The low threshold voltage may be set to any voltage

above 1.3 V by appropriate resistor divider selection.

R3

= R4

V

BATT

1.3 V

−1









the desired low voltage threshold.

Since the LBI input leakage current is less than 10 nA, large val-

ues may be selected for R3 and R4 in order to minimize loading.

For example, a 6 V low threshold may be set using 10 M

Ω for

R3 and 2.7 M

Ω for R4.

ADM666A

SENSE

V

OUT

GND

V

IN

V

SET

LBI

+1.3V TO +15V

OUTPUT

+2V TO +16V

INPUT

R

CL

R2

R1

LBO

SHDN

R3

R4

LOW

BATTERY

OUTPUT

Figure 6. ADM666A Adjustable Output with Low Battery

Detection

High Current Operation

for directly driving the base of an external NPN transistor. Fig-

ure 7 shows a configuration which can be used to provide +5 V

with boosted current drive. A 1

Ω current sensing resistor limits

the current at 0.5 A.

ADM663A

V

OUT1

V

OUT2

GND

V

IN

SHDN

2N4237

V

IN

100

Ω

1.0

Ω

SENSE

V

SET

+

10

µF

+

10

µF

SHUTDOWN

+5V, 0.5A

OUTPUT

Figure 7. ADM663A Boosted Output Current (0.5 A)

The resistor values may be selected by first choosing a value for

R1 and then selecting R2 according to the following equation:

R2

= R1×

V

OUT

1.30

−1









lows large resistor values to be chosen for R1 and R2 with little

degradation in accuracy. For example, a 1 M

Ω resistor may be

selected for R1, and then R2 may be calculated accordingly.

±30 mV so in

most applications, fixed resistors will be suitable.

ADM663A

ADM666A

SENSE

V

OUT(2)

GND

V

IN

V

SET

SHDN

+1.3V TO +15V

OUTPUT

+2V TO +16V

INPUT

R

CL

R2

R1

Figure 5. Adjustable Output

Current Limiting

Current limiting may be achieved by using an external current

the sense resistor exceeds the internal 0.5 V threshold, current

limiting is activated. The sense resistor is therefore chosen such

that the voltage across it will be 0.5 V when the desired current

limit is reached.

R

0.5

I

CL

current limit.

limited to less than the 100 mA absolute maximum rating and

also that the power dissipation will also be within the package

maximum ratings.

If current limiting is employed, there will be an additional volt-

age drop across the sense resistor that must be considered when

determining the regulators dropout voltage.

If current limiting is not used, the SENSE input should be con-

Shutdown Input (SHDN)

The SHDN input allows the regulator to be turned off with a

logic level signal. This will disable the output and reduce

Table I. Output Voltage Selection

GND

+5 V

+3 V

R1/R2

ADJ