Key Specs
| Spec | Value | Condition | Source |
|---|---|---|---|
| Battery Chemistry | Lithium Iron Phosphate | Digi-Key | |
| Battery Pack Voltage | - | Digi-Key | |
| Charge Current (Max) | - | Digi-Key | |
| Current Charging | Constant - Programmable | Digi-Key | |
| Fault Protection | Reverse Current | Digi-Key | |
| Interface | - | Digi-Key | |
| Mounting Type | Surface Mount | Digi-Key | |
| Number Of Cells | - | Digi-Key | |
| Operating Temperature Range | -40°C ~ 125°C (TJ) | Digi-Key | |
| Package Case | 28-WFQFN Exposed Pad | Digi-Key | |
| Programmable Features | Timer | Digi-Key | |
| Supplier Device Package | 28-QFN (4x5) | Digi-Key | |
| Voltage Supply (Max) | 60V | Digi-Key |
When To Use
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LiFePO4 battery pack charging @ constant programmable current: The LTC4000EUFD#TRPBF’s dedicated support for Lithium Iron Phosphate chemistry ensures precise charge termination and cell balancing tailored to LiFePO4’s flat voltage profile. Using a generic synchronous buck controller risks improper charge voltage regulation, potentially causing overvoltage-induced cell degradation or reduced cycle life.
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Battery systems with input voltage up to 60V: The 60V maximum supply rating covers higher-voltage battery stacks or automotive 48V rails with margin for load-dump transients. A controller rated for lower voltages might experience latch-up or device failure when subjected to these spikes.
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Applications requiring reverse current protection: Integrated reverse current fault protection prevents battery discharge back into the input source under fault or power-down conditions. Using a standard synchronous buck controller without this feature can lead to battery drain and unexpected system brownouts during input loss or fault events.
When Not To Use
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Output currents exceeding the device’s rating: The LTC4000EUFD#TRPBF is not specified for very high output currents. For loads requiring current beyond this rating, use a high-current synchronous buck with external FETs that can handle larger conduction and switching losses safely.
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Systems demanding switching frequencies above 500kHz: This part’s switching frequency range is limited compared to some designs. If a smaller inductor footprint or reduced EMI profile is mandatory via >500kHz switching, choose a high-frequency buck controller instead.
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Low-dropout linear regulation with minimal noise: When the input-to-output voltage differential is under 1V and low output noise is critical, the switching topology here is unsuitable. Opt for an LDO regulator to avoid switching ripple and electromagnetic interference.
Application Notes
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The SW (switching node) pin experiences high di/dt and dv/dt; ensure minimal loop area by placing input capacitors close to this pin to reduce EMI and ringing.
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Pins 5 and the timer and fault monitoring pin are noise-sensitive and should be routed away from the SW node and other noisy traces to prevent false fault triggering or timing jitter.
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The exposed pad must be soldered to a large PCB copper area with multiple thermal vias to maintain junction temperature within -40°C to 125°C TJ range under maximum load.
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Use a low-ESR input capacitor to stabilize input voltage and reduce voltage spikes that can stress the internal MOSFETs, avoiding shoot-through or transient latch-up.
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Guard routing is recommended around the reverse current detection circuitry to prevent false triggering from switching noise coupling.
Gotchas
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[Timer programming and thermal derating interaction]: The programmable timer that controls charge termination can inadvertently extend charge time under high-temperature conditions if not adjusted for derating graphs (not in main spec). Result: thermal runaway risk as the device prolongs charging beyond safe limits. Fix: correlate timer settings with thermal derating curves from the datasheet and validate under worst-case ambient conditions.
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[SW node layout causing erratic reverse current fault trips]: Excessive parasitic inductance in the SW loop can induce voltage overshoot and ringing, falsely triggering reverse current fault detection. Symptom: intermittent shutdowns during normal operation visible as irregular pulses on the output. Fix: minimize SW loop inductance by placing input and output capacitors adjacent to the device and using wide copper traces.
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[Minimum load requirement at startup]: The device may not start switching if the load is too light or absent during power-up, causing the output voltage to remain low or unstable. Symptom: absence of switching waveforms on the SW pin and no battery charging. Fix: add a small dummy load or ensure the battery pack has sufficient initial voltage to meet startup conditions.
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[Output capacitor ESR affecting stability]: Using output capacitors with excessively high ESR can destabilize the internal control loop, causing output voltage oscillations under load transients. Symptom: periodic voltage spikes or ringing seen on the output during load changes. Fix: select low-ESR capacitors as recommended and verify loop stability with transient load tests.