AD74115 datasheet(49/103 Pages) AD

49 / 103 page

Data Sheet

AD74115

THEORY OF OPERATION

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Rev. 0 | 49 of 103

Smart Diode

In current sourcing applications, a blocking diode is typically placed

in series with the output FETs to ensure that the digital output

path is protected against reverse overvoltage conditions (when the

I/OP screw terminal voltage is greater than the DO_VDD voltage,

VDO_VDD). This typical configuration is shown in Figure 42.

Significant power can be dissipated in this diode when the digital

output circuit is sourcing high currents (for example, a 500 mA

current source and a diode drop of 0.5 V generates 250 mW of

power).

The AD74115 has a smart diode feature when using the external

digital output function. An additional FET is connected, along with a

resistor and protection Zener, as shown in Figure 44. The gate of

the FET is controlled by the DO_SRC_DGATE pin. When the FET

is disabled, the body diode of the FET conducts. When the FET

is enabled, the power dissipated is calculated by P = I2R, where I

is the sourced current, and R is the RON of the FET. Typically, the

power dissipation in this scenario is <50 mW.

To enable the smart diode option, set DO_EXT_MODE to an exter-

nal source with a smart diode in the DO_EXT_CONFIG register.

Figure 44. Smart Diode Configuration for Current Sourcing with an External FET

AD74115 Datasheet(PDF) 49 Page - Analog Devices