IXI848S1 datasheet(3/5 Pages) IXYS

3 / 5 page

IXYS

www.ixys.com

06/29/05

IXI848

Pin Description and Configuration

SOIC

Name

Description

GND

Ground

R10

Connecting R10 to GND, (R50=N/C) selects a VOUT voltage that is 10X the voltage across

RSENSE.

VOUT

Output voltage proportional to the voltage across RSENSE.

Positive supply terminal and power connection for the external Sense Resistor.

LOAD

Load-side connection to the external Sense Resistor.

N/C

No Connect

N/C

No Connect

R50

Connecting R50 to GND, (R10=N/C) selects a VOUT voltage that is 50X the voltage across

RSENSE.

Detailed Circuit Description

The IXI848 is a precision high side current sense

monitor featuring an input voltage range of 2.7V to

40V, and a selectable ground referenced fixed

gain output of either 10 or 50.

A small voltage developed across an external

sense resistor (RS), is converted to an amplified

ground referenced voltage output at VOUT,

(Figure 1). The amplifier’s non-inverting input is

high impedance making the voltage at that

terminal equal to VIN – (IL) (RS). The amplifier

forces the high impedance inverting terminal to

equal the non-inverting input voltage by turning on

the P-Channel MOS FET.

As the P-Channel MOS FET is biased on by the

amplifier output, current is sourced through RG

(10R or 10R+40R), to produce a voltage equal to

VIN – (IL) (RS) at the inverting input of the amplifier.

This develops a voltage across the inverting input

resistor, R that matches the sense voltage across

RS, plus any associated input offset voltage, (VIO).

Consequently, the voltage at VOUT corresponds

to RG / R.

Output: VOUT = G [ (IL) (RS) + VIO ]

Gain:

G = (RG) (ZM) / R (RG (RG + ZM))

RG = 10R or 50R selectable

Temperature coefficient:

(all on-chip resistors) R = 700ppm / °C typical

RSENSE Component Selection

The RSENSE value should be selected such that the

voltage across RSENSE is at full-scale for the load

current to be monitored. Operating the IXI848 at or

near the full-scale sense voltage will minimize the

error component associated with the input offset

voltage of the internal op amp.

The IXI848 can be configured to measure a wide

selection of currents by using different RSENSE

values. Some common values for typical operation

of the IXI848 are listed in the following table.

Full-Scale

IL (A)

RSENSE

RS (Ω)

Gain

(V/V)

VOUT (V)

VSENSE = 150mV

0.15

1.0

1.5

0.1

1.5

0.01

2.5

100

0.001

Output Impedance

The VOUT output is a current source driving a

33kΩ resistance to ground for a gain of 10, or a

165kΩ resistance to ground for a gain of 50.

Output gain is reduced by resistive loading of the

VOUT terminal. The impedance of the external

monitor load (ZM) should be chosen high enough

to maintain the desired accuracy. Buffering of the

VOUT terminal with a high-impedance input stage

may be required to minimize output errors.

The following formulas quantify the percent error

introduced by output loading:

For a Gain of 10

%ERROR = 100 [RLOAD / (33kΩ + RLOAD) – 1]

For a Gain of 50

%ERROR = 100 [RLOAD / (165kΩ + RLOAD) – 1]

RLOAD = the external load applied to VOUT

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