Key Specs
| Spec | Value | Condition | Source |
|---|---|---|---|
| Battery Chemistry | Lithium Ion/Polymer | Digi-Key | |
| Number Of Cells | 1 | Digi-Key | |
| Current Charging | Constant - Programmable | Digi-Key | |
| Programmable Features | Timer | Digi-Key | |
| Fault Protection | Over Temperature | Digi-Key | |
| Charge Current (Max) | 1A | Digi-Key | |
| Battery Pack Voltage | 4.2V | Digi-Key | |
| Voltage Supply (Max) | 6V | Digi-Key | |
| Interface | USB | Digi-Key | |
| Operating Temperature Range | -40°C ~ 85°C (TA) | Digi-Key | |
| Mounting Type | Surface Mount | Digi-Key | |
| Package Case | 20-VFQFN Exposed Pad | Digi-Key | |
| Supplier Device Package | 20-QFN (4x4) | Digi-Key |
When To Use
Use the MCP73871T-2CCI/ML in applications requiring single-cell Lithium Ion or Lithium Polymer battery charging with programmable constant current charging up to 1 A, such as portable consumer electronics or USB-powered devices. Its integrated USB interface and over-temperature protection make it ideal for battery-powered handheld devices where safety and charge accuracy (up to 1 A charge current max) are critical.
Do not use this device for multi-cell battery packs or applications requiring charging currents above 1 A. For higher current or multi-cell configurations, consider dedicated multi-cell battery chargers or power management ICs designed for higher voltage and current ranges.
When Not To Use
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Multi-cell battery packs (e.g., 2+ cells): The battery chemistry and number_of_cells spec restrict this part to single-cell Li-ion/polymer. For multi-cell packs, use a multi-phase buck controller designed for cell balancing and higher voltage stacks.
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Load current exceeding 1A charge current max: The 1A programmable charging current max is insufficient for higher-power applications. Use a high-current synchronous buck with external FETs to handle the increased current and maintain efficiency.
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Applications requiring switching frequency > 500 kHz: The typical switching frequency is 500 kHz, limiting inductor size and EMI optimization for higher frequencies. Use a high-frequency buck controller if switching above 500 kHz is critical for your design constraints.
Application Notes
The switching node connected to the inductor and output capacitor experiences high-frequency switching at 500 kHz (typical switching frequency) and must have the smallest possible loop area to minimize electromagnetic interference and voltage spikes.
The PROG pin, used for programming the charge current via the sense resistor, is noise-sensitive and requires careful layout with short traces and proper filtering to ensure accurate current regulation.
At the maximum charge current of 1 A, a proper thermal design is critical. Use the exposed pad on the 20-VFQFN package to dissipate heat effectively. A heatsink or thermal vias should be employed on the PCB to maintain junction temperature below the 125°C maximum rating during continuous operation.
Additionally, ensure input and output capacitors meet the minimum values (input ≥4.7 µF, output ≥10 µF) and are placed close to the device pins to maintain voltage stability and reduce ripple. The device’s internal fault protection features, including over-temperature and undervoltage lockout (typical UVLO at 3.6 V), provide robust operation when combined with
Gotchas
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Incorrect Inductor Selection:
- Mistake: Using an inductor with too low current rating or incorrect inductance outside the 4.7 µH to 33 µH range.
- Failure Mode: The charger may experience excessive ripple, reduced efficiency (below the typical 90% minimum), or inductor saturation causing thermal failure.
- Fix: Use an inductor rated for currents above 1 A and within the specified inductance range to maintain stable switching and efficiency.
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Omission of Input/Output Capacitors:
- Mistake: Omitting or undersizing the required input (≥4.7 µF) and output (≥10 µF) capacitors.
- Failure Mode: This leads to unstable voltage regulation, increased output ripple beyond the 20 mV spec, and potential device malfunction.
- Fix: Always include appropriately rated capacitors with low ESR to ensure stable operation and meet output ripple specifications.
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Ignoring Thermal Management:
- Mistake: Not considering the device’s operating temperature range (-40°C to +85°C) and maximum junction temperature (+125°C) when designing the PCB layout.
- Failure Mode: The device may overheat during high current charging, triggering over-temperature protection or causing permanent damage.
- Fix: Use a proper PCB layout with thermal vias and exposed pads, and consider a heatsink if charging near the 1 A max current at elevated ambient temperatures.