IXYS
www.ixys.com 3 08/01/05
IXI848A
Pin Description and Configuration
SOIC Name Description
1 GND
Ground
2 R10
Connecting R10 to GND, (R50=N/C) selects a VOUT voltage that is 10X the voltage across
R
SENSE
.
3 VOUT
Output voltage proportional to the voltage across R
SENSE
.
4 IN
Positive supply terminal and power connection for the external Sense Resistor.
5 LOAD
Load-side connection to the external Sense Resistor.
6 N/C
No Connect
7 N/C
No Connect
8 R50
Connecting R50 to GND, (R10=N/C) selects a VOUT voltage that is 50X the voltage across
R
SENSE
.
Detailed Circuit Description
The IXI848A is a precision high side current sense
monitor featuring an input voltage range of 2.7V to
60V, and a selectable ground referenced fixed
gain output of either 10 or 50.
A small voltage developed across an external
sense resistor (R
S
), 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 V
IN
– (I
L
) (R
S
). 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 R
G
(10R or 10R+40R), to produce a voltage equal to
V
IN
– (I
L
) (R
S
) at the inverting input of the amplifier.
This develops a voltage across the inverting input
resistor, R that matches the sense voltage across
R
S
, plus any associated input offset voltage, (V
IO
).
Consequently, the voltage at VOUT corresponds
to R
G
/ R.
Output: VOUT = G [ (I
L
) (R
S
) + V
IO
]
Gain: G = (R
G
) (Z
M
) / R (R
G
(R
G
+ Z
M
))
R
G
= 10R or 50R selectable
Temperature coefficient:
(all on-chip resistors) R = 700ppm / °C typical
R
SENSE
Component Selection
The R
SENSE
value should be selected such that the
voltage across R
SENSE
is at full-scale for the load
current to be monitored. Operating the IXI848A 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 IXI848A can be configured to measure a wide
selection of currents by using different R
SENSE
values. Some common values for typical operation
of the IXI848A are listed in the following table.
Full-Scale
I
L
(A)
R
SENSE
R
S
(Ω)
Gain
(V/V)
VOUT (V)
V
SENSE
= 150mV
0.15 1.0 10 1.5
1.5 0.1 10 1.5
5 0.01 50 2.5
100 0.001 50 5
Output Impedance
The VOUT output is a current source driving a
33k resistance to ground for a gain of 10, or a
165k 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 (Z
M
) 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 [R
LOAD
/ (33k + R
LOAD
) – 1]
For a Gain of 50
%
ERROR
= 100 [R
LOAD
/ (165k + R
LOAD
) – 1]
R
LOAD
= the external load applied to VOUT
