LTC4151
8
4151ff
For more information www.linear.com/LTC4151
applicaTions inForMaTion
The LTC4151 offers a compact complete solution for high
side power monitoring. With a wide operating voltage
range from 7V to 80V, this device is ideal for a variety of
applications including consumer, automotive, industrial
and telecom infrastructure. The simple application circuit as
shown in Figure 1 provides monitoring of high side current
with a 0.02W resistor (4.096A in full scale), input voltage
(102.4V in full scale) and an external voltage (2.048V in
full scale), all with an internal 12-bit resolution ADC.
Data Converter
The LTC4151 features an onboard, 12-bit ∆Σ A/D
converter (ADC) that continuously monitors three volt
-
ages in the sequence of (V
SENSE
+
– V
SENSE
–
) first, V
IN
second and V
ADIN
third. The ∆Σ architecture inherently
averages signal noise during the measurement period.
The differential voltage between SENSE
+
and SENSE
–
is
monitored with an 81.92mV full scale and 20µV resolu-
tion that
allows accurate measurement of the high side
input
current. SENSE
+
is a Kelvin sense pin for the V
IN
pin and must be connected to V
IN
(see Figure 10) for
proper ADC readout. The supply voltage at V
IN
is directly
measured with a 102.4V full scale and 25mV resolution.
The
voltage at the uncommitted ADIN pin is measured
with
a 2.048V full scale and 0.5mV resolution that allows
monitoring of any external voltage. The 12-bit digital
Figure 1. Monitoring High Side Current and Voltages Using the LTC4151
code of each measured voltage is stored in two adjacent
registers out
of the six total data registers A through F,
with the eight MSBs in the first register and the four LSBs
in the second (Table 2).
The data in registers A through F is refreshed at a frequency
of 7.5Hz in continuous scan mode. Setting control register
bit G4 (Table 6) invokes a test mode that halts updating
of these registers so that they can be written to and read
from for software testing.
The data converter features a snapshot mode allowing us
-
ers to make one-time measurements of a selected voltage
(either
the SENSE voltage, V
IN
voltage, or ADIN voltage).
To enable snapshot mode, set control register bit G7 and
write the 2-bit code of the desired ADC channel to G6
and G5 (Table 6) using a Write Byte command. When the
Write Byte command is completed, the ADC measures the
selected voltage and a Busy Bit in the LSB data register is
set to indicate that the data is not ready. After complet-
ing the conversion, the ADC is halted and the Busy Bit is
reset to indicate that the data is ready. To make another
measurement of the same voltage or to measure another
voltage, first disable the snapshot mode for the previous
measurement by clearing control bit G7, then re-enable the
snapshot mode and write the code of the desired voltage
according to the procedure described above. The Busy Bit
remains reset in the continuous scan mode.
4151 F01
0.02Ω
µ-CONTROLLER
GND
LTC4151
SHDN
V
IN
7V TO 80V
V
IN
V
DD
V
ADIN
SCL
SDA
ADIN
ADR1
SCL
SDA
ADR0
GND
SENSE
+
SENSE
–
3.3V
V
OUT
2k 2k
