LTC4261 datasheet(11/34 Pages) AD

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LTC2945

Rev. C

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2945 F01

0.1µF

VIN

4V TO 80V

RSNS

0.02

VOUT

VADIN

3.3V

VDD

SCL

SDA

INT

GND

ADR0

SCL

VDD

INTVCC

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 infrastruc-

ture. The basic application circuit shown in Figure 1 pro-

vides monitoring of high side current with a 0.02Ω resis-

tor (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, VDD or VSENSE+ second, and VADIN third.

The differential voltage between SENSE+ and SENSE– is

monitored with 25μV resolution (102.4mV full-scale) to

allow accurate measurement across very low value shunt

resistors. The supply voltage at VDD or SENSE+ is directly

APPLICATIONS INFORMATION

measured with 25mV resolution (102.4V full-scale). The

voltage at the uncommitted ADIN pin is measured with

0.5mV resolution (2.048V full-scale) to allow monitoring

of an arbitrary external voltage. A 12-bit digital word corre-

sponding to each measured voltage is stored in two adjacent

registers out of the six total ADC data registers (ΔSENSE

MSB/LSB, VIN MSB/LSB, and ADIN MSB/LSB), with the

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 I2C

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 VDD 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 I2C 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 I2C 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.

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