LINEAR TECHNOLOGY LTC2460 Technical data
CS, SCK,
SDI, SDO
TO CONTROLLER
R
OUT
1k
V
OUT
0.1µF
5V
L
O
A
D
V
OUT
t7
SENSE
R
OUT
R
IN
LTC6102
R
IN
150Ω
V
SENSE
6mΩ
4V TO 60V
V
+
V
–
OUT
+IN
+
–
–INF
–INS
V
REG
0.1µF
–
+
LTC2460
16-BIT ADC
IN
GND
V
CC
DESIGN IDEAS L
3mm × 3mm, 16-Bit ADC Brings
Accurate, Precise High Side
Current Sensing to Tight Spaces
Introduction
Power monitoring circuits are increasingly used throughout automotive,
industrial, communications and
computing applications as electronics
designers strive to continually improve thermal performance, increase
efficiency and generally make their
products more “green.”
The problem is that power monitoring always looks like the perfect feature
until space and cost constraints come
into play. Power monitoring is usually
considered an ancillary function, so
its footprint should be as small as
possible to maximize space available
to the main application. The LTC2460
16-bit Delta-Sigma ADC solves the
space and design cost problem when
paired with one of Linear Technology’s
current sense amplifiers, such as the
LTC6102.
The LTC2460 proves that big-feature ADCs can come in tiny packages.
It is available in a 3mm × 3mm DFN
(or a 12-pin MSOP), and integrates a
10ppm/°C precision reference. The
integrated reference paired together
with an extremely easy to drive input
stage (50nA average input current)
makes it possible to use the LTC2460
with little to no support circuitry.
Measuring Power Means
Measuring Current
Measuring power supply input and
output voltages is fairly straightforward, as any voltage can be scaled
with a simple divider or amplifier and
compared to a voltage reference. Current measurement is generally more
complicated, especially at commonly
used high voltages such as –12V, 24V
and 48V.
To measure current, a small sense
resistor is placed directly in series with
the supply. A current sense amplifier
takes the small voltage drop across this
Linear Technology Magazine • September 2009
Figure 1. A simple and compact high side current sensing solution that combines a high
resolution DS ADC (LTC2460) with a high precision current sensing amplifier (LTC6102).
sense resistor and sources a proportional signal current. If the current is
monitored on a high voltage power supply, an accurate and precise current
sense amplifier, such as the LTC6102,
is required to accurately resolve the
small voltage drop riding on the high
common mode voltage.
Typically the signal current produced by the current sense amp is
converted via a grounded resistor to a
properly scaled voltage, which, in this
case, can be measured directly using
the LTC2460’s easy to drive input.
The 16-bit output data can then be
used to compute power consumption
and efficiency.
mum current out of its OUT pin. This
current is converted into a voltage
across the 1kΩ resistor to ground,
which allows the connected LTC2460
to measure a 0V to 1V input. This input
range spans 80% of the ADC’s input
resolution. Of course, the output of the
current sense amplifier can be scaled
to use as much of the LTC2460’s input
range as needed, while providing for
overrange conditions.
Another advantage to the LTC2460
is the narrow input bandwidth of
approximately 30Hz. This provides
excellent rejection of power supply
ripple noise, and allows accurate
measurement of the DC component
of the current.
Accurate, Precise and Very
Compact High Side Current
Sense Design
Figure 1 shows a 48V, 8A current measurement application. The LTC6102
is a precision current sense amplifier
that offers 10µV maximum input offset voltage, 50nV/°C input offset drift
(maximum), and low 3nA (maximum)
input bias current.
This current sense amplifier has
zero-drift and sources a 1mA maxi-
Conclusion
The LTC2460 and the LTC6102 facilitate a compact, high resolution, high
accuracy current sense solution. The
LTC2460 is a 16-bit ADC in a tiny
package that includes an integrated
precision reference, while the LTC6102
provides high precision, current measurements that in turn can be easily
digitized by the ADC.
by Leo Chen
L
3737
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