Smaller size, higher efficiency for electronic point-of-sale thermal printers


Electronic point-of-sale (EPOS) machines incorporate a tremendous amount of functionality and technology. First, there is the keypad and display to capture and report the user’s input. There may be a barcode scanner for merchandise or a magnetic strip reader for credit cards. There is almost always a thermal printer, because after all, you will want a receipt showing a $0.00 balance when you return a rental car. But all of this functionality in a small space means that at least two things are required: small size and high efficiency.

As in most portable equipment, many internal rails require step-down converters to convert the lower voltage from the battery; I discussed the advantages of a TPS62xxx device for these systems in this post. Perhaps one or two rails need a TPS630xx buck-boost converter to convert the battery voltage up and down to the load. But the thermal printer and display typically need boost converters to generate the higher voltage required to drive these subsystems. While the display needs relatively little current, (supplied by a device like the TPS61046), the thermal printer might require 2-3A for the few seconds that it operates. With the printer’s 9V supply voltage, that’s nearly 30W to deliver just to print your receipt – quite a challenge for a small, integrated device to handle.

TI’s new TPS61088 meets this challenge head on by supplying up to 12.6V at output currents in excess of 3A. Operating from single- or dual-cell lithium batteries, it is an ideal fit for portable devices that need higher voltages at higher currents. By integrating both power MOSFETs into its 4.5mm-by-3.5mm package, the total solution size is reduced by about half compared to existing solutions that must use external MOSFETs.

Plus, integrating both MOSFETs achieves synchronous rectification, increasing efficiency. Figure 1 shows that 96% peak efficiency is possible, while at full power the efficiency is still above 90%. Operating the thermal printer won’t excessively drain the battery, and won’t give users a finger burn from holding the EPOS machine while it is printing.

 

Figure 1: The TPS61088 provides efficiency well above 90%, even at full output power

What other portable applications do you need high voltage at high current?