LTC2947
12
Rev. B
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OPERATION
OVERVIEW
The LTC2947 is a high precision power and energy meter
with integrated sense resistor for currents up to ±30A
and voltages as high as 15V. It measures a total of seven
parameters: current, voltage, power, charge (coulombs),
energy, and run time, as well as its own chip temperature.
It includes three No Latency Δ∑ analog-to-digital con-
verters to simultaneously measure current, voltage, and
power
. It also measures die temperature and derives the
accumulated quantities charge, energy, and time using
an external clock or an on-board oscillator. It stores these
values in internal registers that can be read out via the
serial interface, configurable as either I2C or SPI.
The LTC2947 keeps track of the minimum and maximum
measured values for each of the measured quantities.
Thresholds can be set for each parameter, and the LTC2947
will set the corresponding bit in the Alert register and
optionally alert the host by pulling low on the ALERT pin
when a threshold is exceeded.
A GPIO pin is included that can be used for four different
purposes. It can be configured as a general-purpose-logic
input or output, as an output to automatically control a
fan based on the LTC2947’s internal silicon temperature
measurement or as an input to enable and disable accu-
mulation of charge, energy, and time.
MODES OF OPERATION
Power Up
When all power supply voltages have risen above their
UVLO thresholds, the LTC2947 boots up, sets all regis-
ters to their default state, and enters IDLE mode, where it
waits for further instructions from the host. The LTC2947
requires about 100ms to boot up and enter the IDLE mode.
IDLE
In IDLE mode, all internal circuitry is active but no measure-
ments are being made. From IDLE, the LTC2947 can be
instructed to go into single shot, continuous, or shutdown
modes via the Operation Control control register.
Single Shot (SSHOT):
When the SSHOT bit in the Operation Control register
is set, the LTC2947 takes four measurements (current,
voltage, power, and temperature), and updates the cor-
responding registers and the Minimum/Maximum and
Threshold registers. No time measurements are made and
the Charge and Energy registers are not updated. It then
clears the SSHOT bit in the Operation Control register, sets
the UPDATE bit in Status register and returns to the IDLE
mode. One single shot measurement cycle takes 100ms.
The host can poll the UPDATE bit in the Status register to
detect the completion of the measurement cycle.
Continuous Measurement Mode (CONT)
When the CONT bit in the Operation Control register is set,
the LTC2947 repeatedly measures current, voltage, power,
and temperature, recalculates energy, charge, time and
updates the Minimum/Maximum Tracking and Threshold
registers. Each measurement cycle takes about 100ms.
The current and power ADCs run continuously in this
mode, ensuring that no charge or energy is missed. The
LTC2947 remains in continuous mode until bit CONT of
the Operation Control register is reset by the user. If the
SSHOT bit is set while in continuous mode, the LTC2947
completes the current measurement cycle and then enters
single shot mode, clearing the CONT bit in the Operation
Control register.
Shutdown (SHDN):
When the SHDN bit in the Operation Control register is
set, the LTC2947 goes into shutdown mode, and supply
current reduces to about 10µA. If the device is in the
middle of a measurement cycle, in either single shot or
continuous mode, it completes the cycle before entering
shutdown and clearing the SSHOT or CONT bits. Shutdown
clears the voltage, current, and temperature results, but
preserves the values of the accumulated quantities charge
and energy and all threshold and tracking values.
While in shutdown mode, the LTC2947 continues to monitor
the serial interface. In SPI mode, the LTC2947 transitions
from shutdown to IDLE when CS goes low. In I2C mode,