By Steve Bush 5th May 2022
Halo Microelectronics has introduced a switched capacitor charger dc-dc converter for single Li-ion or Li-po cells that can deliver up to 7A while drawing 3.5A from the supply.
Called HL7139, it is inteded to work from USB PD PSS (power delivery, programmable power supply) sources.
Switched capacitor power converters can be compact and highly efficient, but only reach that high efficiency at certain exact ratios of input to output voltage. Outside these ratios they are far less efficient than inductor-based converters.
To keep its converter operating efficently – it is up to 97.6% efficiency when switching at a 2:1 ratio (halving the input voltage) – Halo is using the PPS variable voltage capability of certain USB PD power sources, telling the PPS source to deliver twice the desired battery terminal voltage. The IC also has a 1:1 mode where it connects its input straight to its output.
“Ac-dc adapter voltage and current [from USB PSS] are programmable in 25mV and 50mA step through PD communication,” Halo sales application engineer Dennis Ha told Electronics Weekly. The “application processor can control the voltage and current depending on battery charging status. HL7139 provides Vin, Iin, Vbat and Ibat charging information [to the host processor] through its 12bit ADC. Therefore, the input voltage is constantly controlled to be 1x or 2x of battery voltage by the application processor.”
The point of adding a 2:1 converter in between the PSS power source and the battery is that it doubles available current, potentially decreasing charge time. As 2:1 switching will not always be appropriate, the host processor has to make the 2:1 or 1:1 decision based on the source current capability of the supply, and the battery’s characteristics.
The penalty for adding this potential for faster charging, aside from component cost, is additional board space, which will be around 5.2 x 7.2mm including the IC and all necessary capacitors, according to the HL7139 data sheet – the package is 2.65 x 2.61mm 36bump WLCSP. The PCB could also have to handle heat dissipation as well (see later).
An integrated front-end series mosfet with control circuitry (QRB in diagram left) handles input over-voltage protection, and regulates temperature (via an external thermistor), input current, battery current and detailed battery voltage. These values are programmable.
As QRB is on the die and regulating battery voltage (by pre-regulating the 2:1 or 1:1 converter), the device will dissipate various amounts of heat if fine control of the input voltage is not available – if the input source is non-PPS, for example.
While being most flexible operating with a host processor through its I2C interface, the IC also has stand-alone modes.
In all cases, operation is from voltages between 3V and 11.7V, corresponding to the ‘5V Prog (3.3 – 5.9V) and ‘9V Prog’ (3.3 – 11.0V) PPS specifications – not the upper reaches of 15V Prog or 20V Prog.
The HL7139 data sheet is not publically available and the part has yet to have a web page. HL7138 will be a similar part, whose differences have yet to be revealed.
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