LT6654BX datasheet(9/14 Pages) AD

9 / 14 page

LT6654BX

Rev. 0

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APPLICATIONS INFORMATION

Figure 11. 175°C LT6654BX-2.5 Sinking 2mA to 3mA

100µs/DIV

–3mA

IOUT

–2mA

VOUT

5mV/DIV/AC

2.5V/DIV

6654BX F11

TA = 175°C

COUT = 1µF

Positive or Negative Operation

In addition to the series connection, as shown on the front

page of this data sheet, the LT6654BX can be operated

as a negative voltage reference. The circuit in Figure 12

shows an LT6654BX configured for negative operation.

In this configuration, a positive voltage is required at VIN

(Pin 8) to bias the LT6654BX internal circuitry. This volt-

age must be current limited with R1 to keep the output

PNP transistor from turning on and driving the grounded

output. C1 provides stability during load transients. This

connection maintains the same accuracy and temperature

coefficient of the positive connected LT6654BX.

Figure 12.

LT6654BX-2.5

VEE

VOUT = –2.5V

0.1µF

6654BX F12

1µF

VEE – VOUT

0.6mA + IOUT

R ≤

OUT

GND

Using the LT6654BX-2.5 to Build a –2.5V Reference

Long-Term Drift

Long-term drift cannot be extrapolated from accelerated

high temperature testing. This erroneous technique gives

drift numbers that are wildly optimistic. The only way

long-term drift can be determined is to measure it over

the time interval of interest. The LT6654BX drift data

was taken on 40 parts that were soldered into PC boards

similar to a real world application. The boards were then

placed into a constant temperature oven with TA = 35°C,

their outputs scanned regularly and measured with an 8.5

digit DVM. Long-term drift curves are shown in Figure 13.

Their drift is much smaller after the first thousand hours.

Figure 13.

LT6654BXMS8

TIME (HOURS)

200

400

600

800

1000

–80

–40

6654BX F13

LT6654BX-2.5 Long Term Drift

Power Dissipation

The allowed power dissipation in the LT6654BX is depen-

dent on the ambient temperature, VIN, the load current

and the package. The LT6654BX package has a thermal

resistance, or θJA, of 163°C/W. A curve that illustrates

allowed power dissipation versus temperature, for the

8-lead MSOP package, is shown in Figure 14. The typical

power dissipation of the LT6654BX-2.5, as a function of

input voltage and output current, is shown in Figure 15.

Maximum allowed output regulated sourcing current is

shown in Figure 16. It can be seen, for VIN = 36V and

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