Datasheet

LTC2945
11
2945fa
For more information www.linear.com/LTC2945
2945 F01
C2
0.1µF
V
IN
4V TO 80V
R
SNS
0.02Ω
V
OUT
V
ADIN
R1
2k
R2
2k
R3
2k
3.3V
V
DD
SCL
SDA
INT
GND
ADR0
SCL
V
DD
INTV
CC
SDAI
SDAO
ADIN
ALERT
ADR1
SENSE
+
GND
SENSE
–
LTC2945
µP
Figure 1. Monitoring High Side Current and Voltages
Using the LTC2945
The LTC2945 offers a compact and complete solution for
high- and low-side power monitoring. With an input com-
mon mode range of 0V to 80V and a wide input supply
operating voltage range from 2.7V to 80V
, this device is
ideal for a large variety of power management applications
including automotive, industrial and telecom infrastructure.
The basic application circuit shown in Figure 1 provides
monitoring of high side current with a 0.02Ω resistor
(5.12A full-scale), input voltage (102.4V full-scale) and an
external voltage (2.048V full-scale), all using an internal
12-bit resolution ADC.
Data Converter
The LTC2945 features an onboard, 12-bit Δ∑ ADC that inher
-
ently averages input noise over the measurement window.
The ADC continuously monitors three voltages in sequence:
ΔSENSE first, V
DD
or V
SENSE
+
second, and V
ADIN
third. The
differential voltage between SENSE
+
and SENSE
–
is moni-
tored with 25μV resolution (102.4mV full-scale) to allow
accurate measurement across very low value shunt resistors.
applicaTions inForMaTion
The supply voltage at V
DD
or SENSE
+
is directly measured
with 25mV resolution (102.4V full-scale). The voltage at
the uncommitted ADIN pin is measured with 0.5mV resolu
-
tion (2.048V full-scale) to allow monitoring of an arbitrary
external voltage. A 12-bit digital word corresponding to
each measured voltage is stored in two adjacent registers
operaTion
The LTC2945 accurately monitors current, voltage, and
power of any supply rail from 0V to 80V. An internal linear
regulator allows the LTC2945 to operate directly from a
4V to 80V rail, or from an external supply voltage between
2.7V and 5.9V. Quiescent current is less than 0.9mA in
normal operation. Enabling shutdown mode via the I
2
C
interface reduces the quiescent current to below 80μA.
The LTC2945 includes a shunt regulator for operation from
supply voltages above 80V.
The onboard 12-bit analog-to-digital converter (ADC) runs
either continuously or on-demand using snapshot mode.
In the default continuous scan mode, the ADC repeatedly
measures the differential voltage between SENSE
+
and
SENSE
–
(full-scale 102.4mV) the voltage at the SENSE
+
or V
DD
pin (full-scale 102.4V), and the voltage at the ADIN
pin (full-scale 2.048V). The conversion results are stored
in onboard registers.
In snapshot mode, the LTC2945 performs a single mea-
surement of one selected voltage or current. Snapshot
mode is enabled by setting the snapshot mode enable bit
in the CONTROL register via the I
2
C interface. A status bit
in the CONTROL register monitors the ADC’s conversion;
when complete, the conversion result is stored in the cor
-
responding data registers.
Onboard logic tracks the minimum and maximum values
for each ADC measurement, calculates power data by
digitally multiplying the stored current and voltage data,
and triggers a user-configurable alert by pulling the ALERT
pin low when the ADC measured value falls outside the
programmed window thresholds. All logic outputs are
stored in onboard registers. The LTC2945 includes an
I
2
C interface to access the onboard data registers and to
program the alert threshold and control registers. Two
three-state pins, ADR1 and ADR0, are decoded to allow
nine device addresses (see Table 1). The SDA pin is split
into SDAI (input) and SDAO (output, LTC2945) or SDAO
(output, LTC2945-1) to facilitate opto-isolation.