LT1027LS8

7

1027ls8f

For more information www.linear.com/LT1027LS8

applicaTions inForMaTion

Effect of Reference Drift on System Accuracy

A large portion of the temperature drift error budget in

many systems is the system reference voltage. Figure 1

indicates the maximum temperature coefficient allowable

if the reference is to contribute no more than 0.5LSB error

to the overall system performance. The example shown is

a 12-bit system designed to operate over a temperature

rangefrom25°Cto65°C.Assumingthesystemcalibration

is performed at 25°C, the temperature span is 40°C. It can

be seen from the graph that the temperature coefficient

of the reference must be no worse than 6ppm/°C if it is

to contribute less than 1LSB error. For this reason, the

LT1027LS8 has been optimized for low drift.

Noise Reduction

Thepositiveinputoftheinternalscalingamplifierisbrought

out as the Noise Reduction (NR) pin. Connecting a 1µF

Mylar capacitor between this pin and ground will reduce

Transientresponseisnotaffectedbythiscapacitor.Start-up

settling time will increase to several milliseconds due to

the 7kΩ impedance looking into the NR pin. The capacitor

must be a low leakage type. Electrolytics are not suitable

for this application. Just 100nA leakage current will result

in a 150ppm error in output voltage. This pin is the most

sensitive pin on the device. For maximum protection a

guard ring is recommended. The ring should be driven

circuit voltage on the NR pin).

Transient Response

TheLT1027LS8hasbeenoptimizedfortransientresponse.

Settling time is under 2µs when an AC-coupled 10mA load

transientisappliedtotheoutput. TheLT1027LS8achieves

fastsettlingbyusingaclassBNPN/PNPoutputstage.When

sinking current, the device may oscillate with capacitive

loads greater than 100pF. The LT1027LS8 is stable with

all capacitive loads when at no DC load or when sourcing

current, although for best settling time either no output

bypasscapactorora4.7µFtantalumunitisrecommended.

An 0.1µF ceramic output capacitor will maximize output

ringing and is not recommended.

Kelvin Connections

Although the LT1027LS8 does not have true force-sense

capability,properhook-upcanimprovelinelossandground

loop problems significantly. Since the ground pin of the

LT1027LS8 carries only 2mA, it can be used as a low-side

sense line, greatly reducing ground loop problems on the

the load or connected via a heavy trace as the resistance

of this trace directly affects load regulation. It is important

to remember that a 1.22mV drop due to trace resistance

Trimming Output Voltage

TheLT1027LS8hasanadjustmentpinfortrimmingoutput

20kΩ with an open-circuit voltage of 2.5V. A ±30mV

to the wiper of a 10k potentiometer connecting between

the output and ground. Trimming output voltage does not

affect the TC of the device.

Figure 1. Maximum Allowable Reference Drift

TEMPERATURE SPAN (°C)

10

0

30

100

1027LS8 F01

1.0

10

20

100

90

80

70

60

50

40

8-BIT

10-BIT

12-BIT

14-BIT