REF191 datasheet(17/24 Pages) AD

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REV. E

REF19x Series

–17–

0.9

0.1

0.8

0.7

0.6

0.5

0.4

0.3

0.2

REF195 DROPOUT VOLTAGE – V

TPC 13. Dropout Voltage vs. Load Current

100

200mV

200 s

TPC 12. Line Transient Response

VOUT

SLEEP (SHUTDOWN)

GND

Figure 1. Simplified Schematic

APPLICATIONS SECTION

Output Short Circuit Behavior

The REF19x family of devices is totally protected from damage

due to accidental output shorts to GND or to V+. In the event

of an accidental short circuit condition, the reference device will

shut down and limit its supply current to 40 mA.

Device Power Dissipation Considerations

The REF19x family of references is capable of delivering load

currents to 30 mA with an input voltage that ranges from 3.3 V

to 15 V. When these devices are used in applications with large

input voltages, care should be exercised to avoid exceeding

these devices’ maximum internal power dissipation. Exceeding

the published specifications for maximum power dissipation or

junction temperature could result in premature device failure.

The following formula should be used to calculate a device’s

maximum junction temperature or dissipation:

T– T

In this equation, TJ and TA are the junction and ambient tempera-

tures, respectively, PD is the device power dissipation, and

θJA is

the device package thermal resistance.

Output Voltage Bypassing

For stable operation, low dropout voltage regulators and refer-

ences generally require a bypass capacitor connected from their

VOUT pins to their GND pins. Although the REF19x family of

references is capable of stable operation with capacitive loads

exceeding 100

µF, a 1 µF capacitor is sufficient to guarantee rated

performance. The addition of a 0.1

µF ceramic capacitor in parallel

with the bypass capacitor will improve load current transient

performance. For best line voltage transient performance, it is

recommended that the voltage inputs of these devices be bypassed

with a 10

µF electrolytic capacitor in parallel with a 0.1 µF

ceramic capacitor.

Sleep Mode Operation

All REF19x devices include a sleep capability that is TTL/CMOS

level compatible. Internally, a pull-up current source to VIN is

connected at the

SLEEP pin. This permits the SLEEP pin to be

driven from an open collector/drain driver. A logic LOW or a 0 V

condition on the

SLEEP pin is required to turn the output stage

OFF. During sleep, the output of the references becomes a high

impedance state where its potential would then be determined

by external circuitry. If the sleep feature is not used, it is recom-

mended that the

SLEEP pin be connected to V

IN (Pin 2).

Basic Voltage Reference Connections

The circuit in Figure 2 illustrates the basic configuration for the

REF19x family of references. Note the 10

µF/0.1 µF bypass net-

work on the input and the 1

µF/0.1 µF bypass network on the

output. It is recommended that no connections be made to Pins 1,

5, 7, and 8. If the sleep feature is not required, Pin 3 should be

connected to VIN.

VIN

SLEEP

1 F

TANT

OUTPUT

0.1 F

10 F

0.1 F

REF19x

NC = NO CONNECT

Figure 2. Basic Voltage Reference Configuration

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