A BLDC motor drive’s passive checklist comes down to three positions: a current-sense shunt resistor rated to survive continuous I²R heating, an MLCC rated above the DC bus voltage, and — on a mains-fed drive — an X1/Y2 safety capacitor at the AC input. Of Walsin Technology (Walsin)’s 11,616 low-ohm current-sense chip resistor rows, only 525 clear both the resistance and the power rating a motor drive shunt actually needs.
Venatech Limited, an authorised Walsin distributor in Hong Kong, built this checklist from Walsin’s chip resistor, MLCC and disc capacitor parametric data: 11,616 low-ohm current-sense resistor rows, 4,095 middle-to-high-voltage MLCC rows and 929 disc capacitor rows. Every part number below is real and checked against our master part-number list. Counts are of part numbers, not pieces.
What does a BLDC motor drive passive checklist need to cover?
Four positions, in order of how often they get re-specified late in a design: the phase current-sense shunt, the DC bus bypass capacitor, an AC-input safety capacitor if the drive runs off mains, and gate-driver decoupling sized to the specific driver IC. This post grounds the first three in real Walsin data; gate-driver decoupling depends on the driver chosen and is outside Walsin’s catalogue.
- Phase current-sense shunt resistor — low-ohm, rated for continuous I²R heating at the drive’s working current.
- DC bus bypass / local decoupling capacitor — MLCC rated above the bus voltage with margin, in a dielectric that holds capacitance under bias.
- AC-input safety capacitor — X1/Y2 (or X1/Y1) line-to-ground, needed only if the drive is powered from mains rather than a low-voltage DC bus.
- Gate-driver decoupling — sized to the specific gate driver’s own datasheet, not covered here.
What shunt resistance and power rating does phase current sensing need?
Whatever resistance keeps the sense voltage inside the current-sense amplifier’s input range at the drive’s peak phase current, and whatever power rating survives the resulting I²R heating continuously. A shunt dissipates power as the square of current, so doubling the sensed current quadruples the heat the resistor must shed — the two specifications are not independent.
Take a drive sensing phase currents up to roughly 10 A RMS through a 10 mΩ shunt. Continuous dissipation is I²R = 10² × 0.010 = 1 W at the nominal operating point, before any overload margin. That is a real constraint, not an assumption: a resistor rated below 1 W will run hot or drift out of tolerance at exactly the current the drive is designed to carry. Designers commonly run a shunt below its full rated power for thermal margin, which pushes the real requirement higher still. The two filters this post applies — resistance at or below 10 mΩ, rated power at or above 1 W — are a reasonable floor for a mid-current BLDC phase shunt, not a figure specific to any one drive.
How many Walsin current-sense resistors actually clear that bar?
525 of them. Walsin publishes two low-ohm current-sense chip resistor families: 10,428 Thick Film Low Ohm Current Sense rows and 1,188 Metal Low Ohm Current Sense rows, 11,616 combined. Apply a resistance filter at or below 10 mΩ and a rated-power filter at or above 1 W together, and only 525 part numbers — 4.5% of the combined line — clear both at once.
| Family | Size | Parts clearing ≤10 mΩ and ≥1 W |
|---|---|---|
| Metal | 2512 (6432) | 335 |
| Metal | 1206 (3216) | 136 |
| Metal | 1225 (3263) | 17 |
| Metal | 0612 (1632) | 17 |
| Metal | 2010 (5025) | 8 |
| Thick Film | 2512 (6432) | 6 |
| Thick Film | 0815 (2037) | 4 |
| Thick Film | 2010 (5025) | 2 |
513 of the 525 are metal-family parts. Only 12 are thick film, and they sit in just three case sizes. A designer who filters Walsin’s catalogue on resistance and power alone, without checking family, will land on a metal part nine times out of ten — which matters for the next question, because the two families do not behave the same way with temperature.
Should a BLDC shunt be thick film or metal?
Metal, if temperature coefficient matters to the measurement — and in a motor drive, where the shunt sits next to a switching power stage, it usually does. Here is one real 2512, 10 mΩ, ±1% electrical point across both families at three power ratings:
| Part number | Family | Series | Rated power | TCR | Match / mismatch |
|---|---|---|---|---|---|
WW25MR010FTL |
Metal | Metal Plate Power Low Ohm Current Sense Chip-Resistor | 1 W | ≦±50 ppm/°C | reference part |
WW25NR010FTL |
Metal | Metal Plate Low Ohm Current Sense Chip-Resistor | 2 W | ≦±50 ppm/°C | match: resistance, tolerance, TCR, case size · mismatch: rated power 2 W not 1 W, different series within the metal family |
WW25AR010FTL |
Metal | Metal Plate Power Low Ohm Current Sense Chip-Resistor | 3 W | ≦±70 ppm/°C | match: resistance, tolerance, case size, series · mismatch: rated power 3 W, TCR ≦±70 not ≦±50 |
WW25WR010FTL |
Thick Film | Thick Film Low Ohm Current Sense Chip-Resistor | 1 W | ≦±1000 ppm/°C | match: resistance, tolerance, case size, rated power · mismatch: TCR ≦±1000 ppm/°C, 20× looser than the metal reference; thick film family, not metal |
The resistance, tolerance and case size are identical across all four. The number that moves is TCR, and it moves by a factor of up to 20. A 10 mΩ shunt reading a motor phase current will see real self-heating and real ambient rise from the adjacent power stage; a ±1000 ppm/°C part drifts roughly 2% in resistance over a 20 °C rise, which is 2% of error injected directly into the current measurement before any amplifier or ADC error is added. The metal parts in the table above hold that drift to roughly a tenth of that figure.
This is also why 513 of the 525 parts that cleared the resistance-and-power filter above were metal: the metal family’s whole value proposition in a motor drive is TCR, and the case sizes it is offered in — 2512 and 1206 chiefly — line up with the power a phase shunt actually needs.
For more current-sense background, see Low-ohm current sense: thick film vs metal. The range is on the Walsin chip resistor page.
What MLCC rating survives the BLDC drive’s DC bus?
Whatever rated voltage clears the bus voltage with margin, in Walsin’s Middle to High Voltage Caps (200V–4kV) series. That series holds 4,095 parts across seven case sizes and voltage steps at 200 V, 250 V, 400 V, 450 V, 500 V, 630 V, 1000 V, 1500 V, 2000 V, 2500 V, 3000 V, 3500 V and 4000 V. Case size tracks voltage: the same capacitance and tolerance climbs case size as the voltage rating climbs.
| Part number | Size | Dielectric | Capacitance | Tolerance | Rated voltage | Match / mismatch |
|---|---|---|---|---|---|---|
0805B102K201 |
0805 | X7R | 1000 pF | ±10% | 200 Vdc | reference part |
0805B102K501 |
0805 | X7R | 1000 pF | ±10% | 500 Vdc | match: size, dielectric, capacitance, tolerance · mismatch: 500 Vdc not 200 Vdc |
1206B102K102 |
1206 | X7R | 1000 pF | ±10% | 1000 Vdc | match: dielectric, capacitance, tolerance · mismatch: 1206 case not 0805, 1000 Vdc |
1812B102K202 |
1812 | X7R | 1000 pF | ±10% | 2000 Vdc | match: dielectric, capacitance, tolerance · mismatch: 1812 case not 0805, 2000 Vdc |
A three-phase BLDC drive running off a 48 V or 60 V battery bus has headroom at 200 Vdc; a drive referenced to a rectified mains bus in the 300–400 Vdc range needs the 500 Vdc or 1000 Vdc step with margin, not the 200 Vdc part. The case size grows with it — 0805 gives way to 1206 and then 1812 for the same electrical value at higher voltage, because the dielectric needs more material thickness to hold off the higher field.
Specification source: Middle & High Voltage MLCC datasheet — https://www.passivecomponent.com/wp-content/uploads/datasheet/WTC_MLCC_Middle_and_High_Voltage.pdf. For dielectric behaviour under DC bias, see MLCC DC bias and voltage derating.
Does a BLDC drive need a safety-certified capacitor?
Only if the drive is powered from AC mains rather than a DC bus. A mains-fed BLDC drive’s input EMI filter needs a line-to-ground capacitor certified to the Y class your approval body recognises — commonly X1/Y2 for an industrial drive. Walsin’s disc capacitor line includes an automotive-qualified X1/Y2 variant alongside the commercial one, which matters for e-mobility BLDC drives such as those in e-bikes and light EVs:
| Part number | Variant | Capacitance | Tolerance | UR (class and voltage) | Match / mismatch |
|---|---|---|---|---|---|
YP0AC101K050 |
Commercial, small size | 100 pF | ±10% | X1-440Vac/Y2-250Vac | reference part |
YP1AC101K050 |
Commercial, small size | 100 pF | ±10% | X1-440Vac/Y2-300Vac | match: capacitance, tolerance, small-size variant, X1 voltage · mismatch: Y2 rated to 300 Vac not 250 Vac |
YP7AC101K060 |
Automotive | 100 pF | ±10% | X1-440Vac/Y2-300Vac 1500Vdc | match: capacitance, tolerance, X1 and Y2 AC voltages vs YP1AC101K050 · mismatch: not listed as small size, carries an additional 1500 Vdc rating the commercial parts do not |
23 of Walsin’s 929 disc capacitor rows carry this automotive X1/Y2 marker. All 23 are at the same X1-440Vac/Y2-300Vac 1500Vdc rating, spanning 100 pF to 10,000 pF.
For the certification classes themselves, see X1/Y1 vs X1/Y2 safety capacitors. The line is on the Walsin disc capacitor page.
The short version
A BLDC current-sense shunt needs resistance and power screened together, not separately — only 525 of Walsin’s 11,616 low-ohm current-sense parts clear ≤10 mΩ and ≥1 W at once, and 513 of those are metal, not thick film, which is the family that also holds TCR an order of magnitude tighter. The DC bus bypass capacitor’s case size grows with its voltage rating in Walsin’s Middle to High Voltage series — check both together, not voltage alone. A mains-fed drive needs an X1/Y2 safety capacitor at the input; an e-mobility drive can specify the automotive variant, 23 part numbers at one rating. We hold no datasheet for current-sense resistors or disc capacitors, so treat every figure above as parametric-export data pending the datasheet.
Send us your BOM and we will tell you, line by line, whether each position clears its own constraint — or ask us to cross one part.
Faster than an email. The cross-reference tool takes a pasted list or a spreadsheet and returns Walsin chip resistor candidates field by field, differences included. Ready stock shows what is physically in Hong Kong, so you can see straight away whether a line is a stock pull or a production slot.
Frequently asked questions
What resistance should a BLDC phase current-sense shunt use?
Whatever keeps the sense voltage inside your current-sense amplifier’s input range at peak phase current, and whatever rated power survives the resulting I²R heating continuously. A 10 mΩ shunt at 10 A RMS dissipates 1 W continuously — a common mid-current design point, not a fixed rule for every drive.
Should a motor drive shunt resistor be thick film or metal?
Metal, if temperature coefficient matters to the measurement. At one real 2512, 10 mΩ, ±1% electrical point, Walsin’s metal parts publish TCR as tight as ≦±50 ppm/°C while the thick film part at the same point publishes ≦±1000 ppm/°C — a 20× difference that becomes real measurement error as the shunt self-heats.
How many Walsin current-sense resistors meet a 10 mΩ, 1 W motor-drive shunt spec?
525 of 11,616 low-ohm current-sense rows — 4.5%. 513 are from the metal family and 12 from thick film, concentrated in the 2512 and 1206 case sizes.
Does Walsin publish a datasheet for its current-sense resistors?
No. Venatech holds only Walsin’s MR automotive and WR general-purpose thick film chip resistor datasheets, neither of which covers the current-sense families. Every specification in this post is read from the parametric export and should be confirmed before a design review.
What MLCC voltage rating does a BLDC drive’s DC bus need?
Above the bus voltage with margin. Walsin’s Middle to High Voltage series runs 200 V to 4000 V across seven case sizes; a 300–400 Vdc rectified-mains bus needs the 500 Vdc or 1000 Vdc step, not the 200 Vdc part, and case size grows with the voltage step at a fixed capacitance and tolerance.
When does a BLDC drive need an X1/Y2 safety capacitor?
Only when the drive is powered from AC mains. A DC-bus-fed drive on a battery or a DC supply does not need a line-to-ground safety capacitor at all; a mains-fed industrial drive typically does, at the X1/Y2 class or higher.
Does Walsin offer an automotive-qualified safety capacitor for e-mobility BLDC drives?
Yes. 23 of Walsin’s 929 disc capacitor rows carry an automotive X1/Y2 marker, all at X1-440Vac/Y2-300Vac with an added 1500 Vdc rating, spanning 100 pF to 10,000 pF.
Three ways to get this answered today
1. Cross a part, free. Paste up to 500 part numbers, or drop an Excel or CSV file, into the free cross-reference tool. It is matched against Walsin’s published catalogue and returns candidates field by field, with every difference from your original stated rather than hidden. Filter by commercial or automotive grade, or for soft termination, high temperature, safety certified, high Q / low ESR or low profile. There is no login and no charge.
2. Send the whole BOM. Upload a BOM and request a quote and we will come back line by line — including the lines we cannot help with, which is usually the more useful half of the answer.
3. Check the shelf before you commit. Ready stock shows what was physically in Hong Kong as at 23 September 2026. It is a dated snapshot, never a live feed, and quantities are never permanent.
Why take our word for any of this? Don’t — check it.
Venatech Limited (威納電子有限公司) is an authorised Walsin Technology distributor in Hong Kong. Confirm that with Walsin rather than with us. On the safety capacitor series we hold UL file E182369, which is searchable in UL’s own public database, together with TUV certificates R50381780 and R50195920 and CQC CQC20001280137 and CQC20001280136, against EN 60384-14:2023, IEC 60384-14:2023 and UL 60384-14. We hold 28 Walsin datasheets, 451 pages, and we will send the one covering your part number. Shipments arrive in original sealed Walsin packaging with lot and date-code traceability, and a certificate of conformity is available per shipment on request.
We will also tell you what we do not hold, which no competitor publishes. REACH, SVHC, conflict minerals, PFAS, China RoHS, ISO 9001, IATF 16949, PPAP, IMDS and a Declaration of Conformity appear nowhere in those 451 pages. You would rather hear that from us now than from your own supplier-approval team later. AEC-Q200 is compliant in Walsin’s own words and never certified, we hold no manufacturer’s end-of-life or allocation list for any brand, and qualification in your own circuit stays with you. We will not tell you a part is equivalent. We will show you where it differs.
Venatech Limited · Unit 207, 2/F, Sun Ling Plaza, 30 On Kui Street, Fanling, N.T., Hong Kong · (852) 2628 4777 · Hong Kong, Shenzhen, Singapore and Jiangmen, with Chengdu in preparation.