What this single-cell charger does — and does not
The BQ2057TS is a linear charger IC for one-cell Lithium Ion or Lithium Polymer packs, with a fixed 4.1V termination voltage. That 4.1V ceiling is important — it is the older Li-Ion standard, not the 4.2V that most current cells expect. If your BOM calls for 4.2V termination, this part will under-charge the cell by 100 mV per cycle. Charge current is constant and programmable via an external resistor — no I2C, no SMBus, just a resistor from the PROG pin to ground. The supply range goes up to 15V, so it runs cleanly from a 5V or 12V rail, but not from a 24V bus without a pre-regulator.
That covers most indoor and portable gear — handheld instruments, IoT gateways, consumer peripherals — but it does not reach automotive under-hood or outdoor telecom cabinet temperatures. If the board sits behind a sun-heated panel or in an engine bay, you need a wider-range part.
Supplied in an 8-TSSOP package (0.173" body width, 4.40 mm) and listed as Tube delivery. Surface-mount only. The 8-TSSOP pitch is 0.65 mm — fine for two-layer boards if you route the thermal pad properly, but the charger's power dissipation (linear regulator) means the copper area under the IC matters for keeping junction temperature below the limit.
The base product number is BQ2057, and the TS suffix indicates the 8-TSSOP package variant.