LTC1657 datasheet(13/16 Pages) LINER

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LTC1657/LTC1657L

This circuit shows a digitally programmable current source

from an external voltage source using an external op amp,

an LT1218 and an NPN transistor (2N3440). Any digital

word from 0 to 65535 is loaded into the LTC1657 and its

output correspondingly swings from 0V to 4.096V. This

voltage will be forced across the resistor RA. If RA is

chosen to be 412

Ω, the output current will range from

0mA at zero scale to 10mA at full scale. The minimum

voltage for VS is determined by the load resistor RL and

Q1’s VCESAT voltage. With a load resistor of 50Ω, the

voltage source can be 5V.

0.1

µF

1657 TA04

5V < VS < 100V

FOR RL ≤ 50Ω

2N3440

412

Ω

IOUT =

≈ 0mA TO 10mA

(DIN)(4.096)

(65536)(RA)

DATA (0:15)

CSLSB

CSMSB

LDAC

CLR

GND

VCC

REFOUT

REFHI

REFLO

X1/X2

LTC1657

µP

5:19

VOUT

–

LT1218

Digitally Programmable Current Source

TYPICAL APPLICATIO S

LTC1657 Datasheet(PDF) 13 Page - Linear Technology

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