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 charge @ constant current: The LTC4000IUFD-1#PBF’s reverse current protection and programmable constant current charging make it ideal for safely managing Lithium Iron Phosphate chemistry, preventing battery damage from discharge through the charger. Using a generic synchronous buck controller without reverse current detection risks battery drain and potential damage during input loss conditions.
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Battery systems with up to 60V supply rails: The 60V maximum supply voltage rating matches mid-voltage battery packs or power sources without margin loss, avoiding breakdown or latch-up seen in controllers rated for 40V or less. Using a buck controller with insufficient input voltage rating can cause permanent device failure under transient or steady-state conditions.
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Surface mount designs requiring low-profile 28-WFQFN packages: The exposed pad 28-WFQFN package supports efficient thermal dissipation in compact PCB layouts, critical for high power charging at elevated junction temperatures up to 125°C. Alternative packages without exposed pads often overheat under similar power dissipation, leading to thermal shutdown or reliability degradation.
When Not To Use
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Output current demands exceeding this part’s constant programmable current capability: The LTC4000IUFD-1#PBF is limited by its integrated current control and thermal constraints. For higher current loads, a multi-phase buck controller is required to distribute thermal and electrical stress safely.
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Applications requiring ultra-low quiescent current during long standby: This part’s quiescent current is not optimized for μA-level sleep current. For battery-powered sensor nodes or coin cell devices, use a low-IQ PFM buck to prevent premature battery depletion.
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Input voltages below 1V differential with output and strict noise requirements: The LTC4000IUFD-1#PBF is not optimized for low dropout operation or ultra-low noise. Use an LDO regulator when input-to-output voltage difference is less than 1V and noise is critical.
Application Notes
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The switching node (SW) pin must be routed with low inductance and minimal copper area loops to reduce EMI and voltage overshoot; this node switches at high di/dt and dv/dt.
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Pins 3 and the current sense and timer programming pin are noise-sensitive; keep their traces short, shielded from switching node, and use local ground reference to avoid false triggering or timing errors.
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The exposed pad must be soldered directly to a large PCB thermal plane with multiple vias to maintain junction temperature within -40°C to 125°C TJ range under maximum load.
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Reverse current protection relies on proper sense resistor placement and layout symmetry; asymmetrical routing can cause inaccurate current detection and unexpected reverse current flow.
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The timer programming pin must not be left floating; it requires a defined resistor to ground or supply to avoid unpredictable charge termination behavior.
Gotchas
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[Timer pin floating]: Designers sometimes leave the timer programming pin open, assuming internal defaults suffice. This causes erratic charge termination timing, with the charger failing to stop at the set limit, leading to battery overcharge or incomplete charge cycles. Fix: Always connect the timer pin through a resistor as specified to ground or supply to define termination time explicitly.
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[Reverse current sense resistor layout]: Placing the current sense resistor far from the controller or on a high-inductance path leads to noise injection and false reverse current detection. Symptoms include premature charge shutdown or oscillation in the charge current. Fix: Locate the sense resistor as close as possible to the IC pins with Kelvin sensing and minimize loop area.
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[SW node trace length excessive]: Long or wide SW traces increase parasitic inductance and cause voltage spikes and ringing, which can trigger internal device latch-up or damage over time. Oscilloscope waveforms show ringing >10V above input voltage. Fix: Minimize SW trace length and use ground plane shielding to suppress switching noise.
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[Startup with no battery load]: The LTC4000IUFD-1#PBF can appear non-functional if the battery pack is disconnected or has an open cell during power-up, as the internal logic waits for valid voltage/current feedback. Symptom is no switching activity or output current seen on scope. Fix: Ensure battery presence or provide a minimum load path during initial power-up to allow proper startup sequencing.