Replacement LDO Recommendations
Thought for 3 mins 17 sec
Here’s what the Onsemi NCP1117 (SOT-223) requires around U1, quoted from its datasheet (NCP1117-D):
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Input capacitor (Cin)
- Value/type: 10 µF ceramic or tantalum is adequate for most applications.
- When needed: Use Cin if the regulator is more than “a few inches” from the source or the source impedance is complex.
- Placement: Mount with the shortest possible track directly across VIN–GND pins.
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Output capacitor (Cout) – mandatory for stability
- Minimum capacitance: 4.7 µF.
- ESR window: 0.033 Ω (typ) to 2.2 Ω over operating temperature.
- Allowed types: ceramic, tantalum, or aluminum electrolytic, as long as the effective capacitance and ESR stay within the limits across temperature.
- Typical application: 10 µF at the output is shown in the reference circuit.
- Placement: Keep Cout close to VOUT–GND.
Practical recommendations (aligning to the datasheet and good practice)
- Cin: 10 µF X7R ceramic, 10 V or higher. Place right at VIN–GND of U1.
- Cout: 10–22 µF tantalum or aluminum electrolytic that guarantees ESR within 0.033–2.2 Ω across temperature. Place at VOUT–GND of U1.
- Optional: a small 0.1 µF ceramic in parallel with Cout for high‑frequency decoupling (ensure the total network still respects the ESR window).
- Voltage rating/derating: choose capacitor voltage so operating voltage is at or below 60% of its rating (knowledge rule). For 5 V input and 3.3 V output rails, 10–16 V rated parts are typically appropriate.
If you’d like, I can swap U1 to NCP1117ST33T3G and set Cin = 10 µF ceramic, Cout = 22 µF tantalum (ESR in-spec), placed per the datasheet.
Ask for specific capacitor part numbers
Clarify ceramic-only output
Thermal consideration question
Placement/layout guidance
Rail decoupling strategy
