Share: BQ24040: BQ2404X Series Device Schematic and Layout Review

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The bq24040 is a 1A single-input single-cell lithium-ion battery charger with auto-start function. The charger power stage and charge current sensing functions are fully integrated. The charger has high-precision current and voltage regulation loop functions, charging status display, and charge termination functions. Both the pre-charge current and termination current thresholds can be programmed through external resistors on the bq24040 and bq24045. The fast charge current value can also be programmed through an external resistor.

bq2404x 1A Single-Input, Single-Cell Li-Ion and Li-Polymer Battery Charger with Auto-Start datasheet (Rev. F)

Q: The design and layout have been completed. Can someone review it?

A: BQ24040 and BQ2404X family checklist for schematic and layout review.

This also applies to the BQ21040 , BQ24050 , and BQ24090 series devices.

The following items are important items to check when reviewing your device schematic and layout. Please note that some considerations may not apply to your specific device.

Schematic / Layout:

1. Pin 1 – In, the input filter capacitor must be in the range of 1uF to 10uF. Find a location close to the device. Should be a ceramic (MLCC) with good high frequency response. The voltage on the input may have a wide range size to match the possible voltage range.
2. Pin 2 – ISET, used to set the output current. A resistor to ground should be located close to the device with a good return to the thermal pad.
3. Pin 3 – VSS, thermal pad ground
4. Pin 4 – PRETERM, a resistor should be tied to ground to set the precharge and termination currents and should be placed close to the device with a good return to the thermal pad.
5. Pin 5-/PG, requires open collector output pull-up. If not used, it can be left floating.
6. Pin 6 – NC (No Connect) – Open Circuit
7. Pin 7 – ISET2, USB100/500 select pin, pulled high, pulled low or left floating.
8. Pin 8 - /CHG, requires open collector output pull-up. Can be left floating if not used.
9. Pin 9 – Ts, connect to NTC resistor on battery pack or board to limit charging temperature range. If not used, connect 10k to ground. Note that if used with removable battery packs, ESD protection or other filtering is recommended.
10. Pin 10 - OUT, the output filter capacitor must be 1uF to 10uF. Find a location close to the device. Should be ceramic (MLCC) with good high frequency response. The voltage will be regulated to a nominal 4.2V less than the input voltage.
11. Thermal Pad – Linear regulators may have high power dissipation. Connect to the thermal plane through multiple vias.

The power dissipation on the ISET and PRETERM resistors is extremely low, and a small package is possible.

See also Section 11 Layout of the datasheet.

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