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LTC2940 Datasheet(PDF) 10 Page - Linear Technology |
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LTC2940 Datasheet(HTML) 10 Page - Linear Technology |
10 / 32 page LTC2945 10 2945f 2945 F01 C2 0.1μF VIN 4V TO 80V RSNS 0.02Ω VOUT VADIN R1 2k R2 2k R3 2k 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 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, VDD or VSENSE+ second, and VADIN third. The differential voltage between SENSE+ and SENSE– is moni- tored with 25μV resolution (102.4mV full-scale) to allow accuratemeasurementacrossverylowvalueshuntresistors. APPLICATIONS INFORMATION The supply voltage at VDD 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 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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