Data Sheet

LT8440

analog.com

Rev. 0

7 of 22

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

θJA

= 39.3°C/W, θJCTOP = 80.9°C/W, θJCBOT = 5.8°C/W

THE EXPOSED PAD (PIN 9) IS RTN AND MUST BE SOLDERED TO PCB.

Figure 4. Pin Configuration

Table 3. Pin Descriptions

PIN

NAME

DESCRIPTION

1, 2

LINEA,

LINEB

Connect each of these pins through their own resistors to the terminals of the twisted

pair to sense the line voltage. The resistors should be around 20kΩ. A smaller

resistance is insufficient for intrinsic safety if the LT8440 is damaged, and a larger

resistor negatively impacts the accuracy of the voltage measurement. The polarity of

the connection to the twisted pair does not matter. The LT8440 will adjust the limit for

the current it allows through the internal pass device according to the absolute voltage

between these pins.

3, 4,

9 (EP)

RTN

Connect these pins to the RTP pins of another instance of the LT8440 or to the return

terminal of the rectifier for the twisted pair. The current for the load circuits will exit

from these pins after passing through the LT8440.

5

RTP

Connect these pins to the RTN pins of another instance of the LT8440 or to the

common return path for all the field device load circuits.

6

COMP

Optional pin for additional compensation of the shunt regulation loop. If unused, leave

it floating. See the Applications Information section for more details.

7

SHUNT

Connect this pin to load positive. The internal shunt transistor will draw current as

necessary to maintain about 500mW through the rectifier for the twisted pair. Optional

resistors can reduce the power dissipation of LT8440. If unused, leave it floating.

8

VIN

The quiescent current for the LT8440 is drawn through this pin, where the input

voltage is applied. Connect it to the output of the rectifier of the twisted pair through a

resistor. The resistor should be around 15kΩ. A smaller resistor is insufficient for

intrinsic safety if the LT8440 is damaged, and a larger resistor limits the LT8440's

operating range unnecessarily. See the Applications Information for more details on

how to select this resistor.