IOUT = IOUT_MAX x

DAC10 + 1

128

IOUT_MAX =

1

RSET

AVDD

20

x

SET

LM8342

RSET

I

2

C COMPATIBLE BUS

IOUT

CONTROLLER

DIGITAL/

ANALOG

CONVERTER

OUT

AVDD

MEMORY

+

-

LM8342

SNOSAM0B – NOVEMBER 2005 – REVISED MARCH 2013

www.ti.com

PRINCIPLE OF OPERATION OF THE LM8342

The LM8342 is an integrated combination of a digitally controlled current sink and a non-volatile register (7 bits

EEPROM). Writing data can be done using the I2C compatible interface. Data can be written to a volatile register

and can also be stored in the non-volatile EEPROM. A simplified block diagram of the LM8342 is given in

Figure 24.

Figure 24. Block Diagram of the LM8342

The maximum output current of the LM8342 can be defined using an external resistor RSET in combination with

an analog reference voltage AVDD. This maximum current can be calculated using Equation 1.

(1)

The operating range for the output current is given in the Electrical Characteristics table. Variations of the voltage

reference AVDD or the external resistor RSET will affect this output current. Using a resistor with a low temperature

coefficient is recommended.

The relative value of IOUT with respect to the maximum current can be controlled digitally in 128 steps, using the

internal DAC. This results in an output current described by Equation 2.

(2)

Using the serial interface bus the operator can store the DAC value in the LM8342s 7-bits volatile register

temporarily, or permanent in the EEPROM. During a start-up sequence the LM8342 will copy the contents of the

EEPROM to the register setting the DC value.

CONTROLLING THE DEVICE

The LM8342s current sink can be programmed using a serial interface bus. Additional functions (e.g. storing data

in the EEPROM) can be controlled in combination with external inputs. Table 1 shows the pins of the LM8342

and gives a short functional description.

Table 1. Pin Descriptions

Pin name

Function

SDA & SCL

The LM8342 output current can be controlled using the serial I2C compatible interface. This 2-

(Serial interface bus)

Wire interface uses a clock and a data signal. New values can be written to the memory, or the

current value can be read back from the device. The I2C compatible interface is discussed in

more detail in the next chapter.

AVDD

Analog reference voltage for the DAC.

VDD

Supply voltage for both the analog and digital circuitry.

SET

An external resistor RSET connected to the SET pin determines the maximum output current, see

Equation 1.

OUT

The output of the programmable current sink.

12

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