Batteries & Fuel Cells
Figure 5. Default 12 V lead-acid temperature profile
Figure 6. Solar panel global sweep Figure 4. Default Li-ion JEITA profile
can do the monitoring, and inform the host controller when this limit has been reached. At this point, the host can switch off the main load and enter a low power state.
The telemetry system is also capable of measuring the battery series resistance (BSR), which serves as an indication of battery health. The BSR measurement can be set to run automatically, and an alert can be configured to notify the host controller that a custom high BSR limit has been exceeded, at which point the host may signal to the user that the battery needs to be replaced. When the input supply is removed and the system is powered by the battery, the LTC4162 automatically turns off the telemetry system to conserve battery life. If a measurement is needed, the telemetry system can be forced into action via an I2C command, at which point it enters a slower, low power telemetry mode where measurements are taken every five seconds. If desired, the telemetry rate can be set to the high
14 April 2019
speed 11 ms/read rate at any time. Similarly, for lead-acid batteries, a temperature compensation algorithm linearly decreases the target voltage in each charging stage as temperature rises. These voltages can be offset with I2C commands, and the compensation slope can be modified by simply changing the thermistor.
MPPT and input regulation For the sake of simplicity, many solar panel regulation circuits set the maximum power point voltage as a constant value. In reality, VMPP drifts with illumination, and a partially obstructed solar panel can have multiple power peaks. By sweeping the entire voltage range of the panel connected to its input supply, the LTC4162’s advanced maximum power point tracking (MPPT) algorithm accounts for all variables, always settling on the max power point. In addition to occasional sweeps of the solar panel range, the LTC4162 dithers the input regulation voltage, constantly
Components in Electronics
seeking out minor changes in the VMPP. These features require no custom programming, so panels can be switched out without charger modification. The benefits of input regulation extend beyond solar panel sources. Many USB cables, for example, have a significant amount of series impedance and this causes voltage droops at the charger input when current is drawn. The undervoltage current limit feature of the LTC4162 regulates this current such that a minimum voltage is maintained at the input.
USB power delivery LTC4162 is also compatible with the USB Power Delivery specification that allows up to 100 W of power to be sourced through a USB Type C cable. The input current limit of the LTC4162 can be configured such that an input adapter is not overloaded. When the input current limit is reached, the system load can still pull as much power as it needs from the input, but the battery charge current is reduced such that the input current limit is not exceeded. For USB PD, this means
that one LTC4162 circuit can be supplied by various power adapter profiles.
Low power ship mode When a product needs to be shipped or stored for a long period of time, an I2C command can place the LTC4162 into a low power state, reducing the current drain on the battery to about 3.5 µA. Optionally, the circuit can be configured to cut power from the system load during this period.
Conclusion Before members of a design team spend all day reading data sheets for various battery chargers, power monitors, and solar regulators— before spending hours writing code for a custom temperature- dependent charging algorithm and manually polling measurements to detect when limits are exceeded—they may want to consider reaching for a one-size- fits-all battery charger. There is a good chance the LTC4162 is the best device for the job.
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