ADM666A データシートの表示（PDF） - Analog Devices

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ADM666A

Tri-Mode: +3.3 V, +5 V, Adjustable Micropower Linear Voltage Regulators

Analog Devices 

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

The input leakage current on VSET is 10 nA maximum. This al-

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

degradation in accuracy. For example, a 1 MΩ resistor may be

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

The tolerance on VSET is guaranteed at less than ± 30 mV so in

most applications, fixed resistors will be suitable.

+2V TO +16V

INPUT

VIN

ADM663A

ADM666A

SHDN

GND

SENSE

VOUT(2)

RCL

VSET

+1.3V TO +15V

OUTPUT

R2

R1

Figure 5. Adjustable Output

Table I. Output Voltage Selection

VSET

GND

VIN

R1/R2

VOUT

+5 V

+3 V

ADJ

Current Limiting

Current limiting may be achieved by using an external current

sense resistor in series with VOUT(2). When the voltage across

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.

RCL

=

0. 5

ICL

where RCL is the current sense resistor, ICL is the maximum

current limit.

The value chosen for RCL should also ensure that the current is

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-

nected to VOUT(2).

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

ADM663A/ADM666A

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

where R3 and R4 are the resistive divider resistors and VBATT is

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 MΩ for

R3 and 2.7 M Ω for R4.

+2V TO +16V

INPUT

R3

R4

VIN

SENSE

RCL

ADM666A VOUT

LBI

SHDN GND

VSET

LBO

LOW

BATTERY

OUTPU T

+1.3V TO +15V

OUTPUT

R2

R1

Figure 6. ADM666A Adjustable Output with Low Battery

Detection

High Current Operation

The ADM663A contains an additional output, VOUT1, suitable

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.

VIN

+

10µ F

SHUTDOWN

VIN

VOUT1

ADM663A VOUT2

SHDN

2N 4237

100Ω

1.0Ω

VSET

GND

SENSE

+

10µF

+5V, 0.5A

OUTPUT

Figure 7. ADM663A Boosted Output Current (0.5 A)

REV. 0

–5–

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