Key Specs
| Spec | Value | Condition | Source |
|---|---|---|---|
| Battery Chemistry | Lithium Iron Phosphate | Digi-Key | |
| Battery Pack Voltage | 4.6V ~ 14V | Digi-Key | |
| Charge Current (Max) | 3.15A | Digi-Key | |
| Current Charging | Constant - Programmable | Digi-Key | |
| Fault Protection | Over Current, Over Voltage, Short Circuit | Digi-Key | |
| Interface | USB | Digi-Key | |
| Mounting Type | Surface Mount | Digi-Key | |
| Number Of Cells | 1 | Digi-Key | |
| Operating Temperature Range | -40°C ~ 85°C | Digi-Key | |
| Package Case | 36-WFBGA, WLBGA | Digi-Key | |
| Programmable Features | Current, Timer, Voltage | Digi-Key | |
| Supplier Device Package | 36-WLP (2.758x2.758) | Digi-Key | |
| Voltage Supply (Max) | 13.4V | Digi-Key |
When To Use
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Single-cell LiFePO4 battery charger @ 3A: The MAX77787HEWX+T’s 4.6V to 14V input range and 3.15A programmable constant charge current perfectly match a 1-cell LiFePO4 pack charging scenario. Using a generic charger without overcurrent and short-circuit protection risks thermal runaway or permanent cell damage during fault conditions.
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USB-powered 1-cell LiFePO4 system with tight thermal budget: The integrated surface-mount 36-WLP package and programmable current/voltage/timer features allow precise thermal and charge management within the -40°C to 85°C operating range. A non-programmable charger risks overcharging or uncontrolled heating due to lack of fine current and timer control.
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Battery pack with USB interface requiring fault protection: The built-in overcurrent, overvoltage, and short-circuit protections ensure safe operation over USB input variations up to 13.4V max supply. Using a bare synchronous buck controller without integrated protection can cause latch-up or damage to the battery in transient fault conditions.
When Not To Use
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System requiring >3.15A continuous charge current: The 3.15A max charge current rating disqualifies this part. Use a multi-phase buck controller instead, which supports higher output currents without thermal or current limiting failures.
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Input voltage above 14V (e.g., 24V rail): The maximum supply voltage of 13.4V is too low for higher-voltage systems. Use a synchronous buck controller designed for higher input voltages to avoid breakdown or shoot-through events.
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Low dropout linear regulation with <1V differential: This part is a switching charger with programmable current and voltage but not optimized for low dropout noise-sensitive loads. Use an LDO regulator for low noise and minimal dropout when input-output differential is under 1V.
Application Notes
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The switching node (SW) pin carries high di/dt and voltage spikes; keep the loop area minimal by placing input capacitors close and routing SW away from sensitive analog pins (#12, #14).
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Pins #5 and #7 are noise-sensitive feedback and current-sense inputs; route their traces with ground guard rings and avoid crossing noisy traces to prevent erratic regulation or false fault triggers.
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The 36-WLP package requires a solid thermal pad under the device to ensure heat dissipation; use multiple vias connecting to inner ground planes.
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The USB interface pins must be protected from ESD and voltage transients; place appropriate TVS diodes and series resistors on USB lines.
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Programmable timer settings affect charge termination; ensure firmware or controller sequencing properly configures these registers before enabling charging to avoid incomplete charge cycles.
Gotchas
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[Mistake]: Assuming the part can maintain full 3.15A charge current continuously at 85°C ambient without thermal derating.
What happens: The device enters thermal shutdown intermittently, causing charge current dips and extended charge times.
Fix: Check the thermal derating curves in the datasheet and verify PCB thermal impedance; use thermal simulation to confirm junction temperature remains below limit during worst-case ambient and charging conditions. -
[Mistake]: Using output capacitors with excessively high ESR expecting better ripple reduction.
What happens: High ESR causes loop instability leading to oscillations visible on the SW node and output voltage ripple, triggering false fault detection or erratic charging behavior.
Fix: Use low-ESR ceramic capacitors as recommended and verify loop stability with an oscilloscope during bring-up. -
[Mistake]: Routing the SW node trace over or near sensitive analog pins (#5, #7) due to layout constraints.
What happens: Injected switching noise corrupts current sense signals, causing intermittent overcurrent faults or premature charge termination.
Fix: Separate SW routing physically and use ground guard rings; maintain at least 3mm clearance from sensitive pins. -
[Mistake]: Powering the device from a USB source that occasionally dips below 4.6V during startup transients.
What happens: The charger fails to start or behaves erratically due to undervoltage lockout, resulting in no charge current and no fault indication.
Fix: Measure USB voltage at the device input during power-up; add bulk capacitance or a power-good supervisory circuit to ensure stable input voltage above 4.6V before enabling the charger.