Adding a multi-cell battery system to single-cell designs: Page 4 of 5

March 22, 2013 //By Daniel Acevedo
Adding a multi-cell battery system to single-cell designs
Daniel Acevedo, applications engineer, Texas Instruments explains how a front-end power management unit enables system designers to continue using their single-cell-based designs, while increasing efficiency of subsystems needing higher input voltage.
simplified block diagram of a tablet using the front-end PMU is depicted in Figure 1 . The two- or three-cell series Li-Ion or Li-Polymer batteries are illustrated on the left, powering and/or being charged by the TPS65090. In the top left is an AC adapter. This is a DC supply at a voltage above that of the batteries. This supply charges the batteries and powers the system during charge. In this configuration, with the front-end PMU, the AC adapter also can be supplemented by the battery stack in a high-current load situation, such as a system start-up.

To the right of the batteries is a front-end PMU. To the right sits the system PMU, then the microprocessor. Neither need to tolerate more than five volts. At the bottom are the peripherals or modules. These can be powered through the frontend PMU’s load switches. Additionally, the front-end PMU contains a 10-bit, sixteen channel, analog-to-digital converter (ADC) and provides an I 2C bus to allow for configuration and for the processor to read voltages and load currents from the ADC.


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Figure 1: Tablet design with multi-cell battery stack simplified block diagram.

The simplified functional block diagram pictured in Figure 2 illustrates these features, as well as the required external components.


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Figure 2: Functional block diagram of a frontend PMU
Two for the price of one
As tablet designs are often rooted from their predecessor, the smartphone, the primary design challenges are improving run-time and having a timely release to market. Shifting to a multi-cell battery stack and preserving the validated single-cell design is possible using a front-end PMU. A device like the TPS65090 allows for the upgrade to a multi-cell Li-Ion or Li-Polymer battery stack, with the front-end PMU protecting and managing the system while allowing the WLED driver to take advantage of the higher battery stack output voltage. This increases
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