MP1584 Calculator (NRFND) – Resistors, RFREQ, Inductor + MP2338 Notes
Answer
NRFND. MPS lists the MP1584 as not recommended for new designs. The product page says it continues in production for existing customers and points new designs to the MP2338GTL. The datasheet is watermarked "Not recommended for new designs, refer to MP2338". Use this calculator to repair, tune or copy an existing MP1584 design. With R2 = 40.2 kΩ, R1 = 50.25 kΩ × (VOUT − 0.8 V), so 3.3 V needs 127 kΩ. RFREQ (kΩ) = 180000 / fs(kHz)^1.1 (100 kΩ is about 900 kHz). ton = VOUT / (VIN × fs) must stay at or above 100 ns. Source: MPS MP1584 datasheet Rev 1.0, pp.3, 9–10, and the product page, both checked 2026-10-26.
Calculator
How it works
The default ripple target is 30% of the 4.0 A minimum current limit, which is 1.2 A. That is a conservative reading of the datasheet’s “maximum switch current limit” wording. The inductor formula is L = VOUT / (fs × ΔIL) × (1 − VOUT / VIN,max). Peak current is ILOAD + ΔIL/2, checked against the 4.0 A minimum limit. Headroom under 3 V, VIN at or below 5 V, or VOUT/VIN above 65% raises the external bootstrap-diode warning.
A chosen inductor replaces the default ripple: ΔIL is computed from that L instead. The datasheet compensation table pairs 5 V with 15–22 µH. If you use those R3/C3 values, stay inside that inductor range. At light load, a 3.3 V output wants VIN above 6.3 V in the datasheet example (p.14).
MP2338 for new designs
MPS names the MP2338GTL as the alternative. It is not pin-compatible, so it needs a new layout.
| Item | MP1584 (Rev 1.0) | MP2338 (Rev 1.0) | Impact |
|---|---|---|---|
| Package | SOIC8E | SOT583, 8 pins, 0.5 mm pitch | New footprint |
| Pinout | 1 SW, 2 EN, 3 COMP, 4 FB, 5 GND, 6 FREQ, 7 VIN, 8 BST | 1 PG, 2 VIN, 3 SW, 4 GND, 5 BST, 6 EN, 7 SS, 8 FB | Not pin-compatible |
| VIN | 4.5–28 V / 30 V abs | 4.5–28 V / 30 V abs | Same |
| VOUT | 0.8–25 V | 0.5 V to 0.95 × VIN, or 16 V max | No outputs above 16 V |
| Output current | 3 A | 3 A continuous | Same rating |
| Current limit | 4.0 / 4.7 A peak | Low-side valley 2.9 / 3.75 / 4.6 A, hiccup | Different limit type |
| Rectification | Non-synchronous, external Schottky | Synchronous, 115 mΩ / 55 mΩ | Diode removed |
| Frequency | 100 kHz–1.5 MHz, set by RFREQ | 450 kHz typical (350–550 kHz), not adjustable | No RFREQ; resize L |
| Compensation | External R3/C3 on COMP | Constant on-time; no COMP pin | Fewer parts |
| Feedback | 0.8 V (0.776–0.824 V) | 0.5 V (492.5–507.5 mV over temperature) | New divider |
| EN | 1.5 V rising, floats on | 1.2 V rising, internal 1 MΩ to GND | Tie EN high or use a divider |
| UVLO | 3.0 V rising | 3.96 V rising | Higher start voltage |
| Soft-start | Internal, 1.5 ms | External SS capacitor; 22 nF is about 1.5 ms | Add C_SS |
MP2338 resistors: VOUT = 0.5 V × (1 + R1/R2). Datasheet Table 1 (p.18), recomputed:
| VOUT | R1 | R2 | Result | L |
|---|---|---|---|---|
| 1 V | 51 kΩ | 51 kΩ | 1.000 V | 2.2 µH |
| 1.8 V | 51 kΩ | 16.9 kΩ | 2.009 V | 3.3 µH |
| 2.5 V | 51 kΩ | 12.7 kΩ | 2.508 V | 4.7 µH |
| 3.3 V | 51 kΩ | 9.09 kΩ | 3.305 V | 6.8 µH |
| 5 V | 90.9 kΩ | 10 kΩ | 5.045 V | 6.8 µH |
| 12 V | 255 kΩ | 11 kΩ | 12.09 V | 10 µH |
Table 1 prints R2 = 16.9 kΩ for 1.8 V. Equation 4 on the same page gives 2.009 V with those values. For 1.8 V, Equation 4 gives R2 = 19.6 kΩ (E96) with R1 = 51 kΩ, which is 1.801 V. That 19.6 kΩ figure is our calculation, not a datasheet value. Figure 6 also shows 51 kΩ / 16.9 kΩ.
The text suggests 5–30 µA through R2. The Table 1 values draw about 50 µA (0.5 V / 10 kΩ). Both come from the datasheet. The auto-start example 191 kΩ / 49.9 kΩ gives about 6.5 V (recomputed 6.52 V). On-time at 450 kHz is 463 ns for 24 V to 5 V and 79 ns for 28 V to 1 V, both above the 50 ns minimum. Above 92% duty, on-time extends and frequency can fall to a 250 kHz minimum.
MP2338 does not fit outputs above 16 V, a set frequency other than about 450 kHz, or a board that has to stay SOIC8E. This page does not cover other parts.
Part numbers
MP1584EN (SOIC8E). Tape and reel suffix –Z, RoHS suffix –LF, for example MP1584EN–LF–Z. MP2338GTL (SOT583), for example MP2338GTL–Z. Information only.
Disclaimer
Calculations use MPS datasheet values. Module boards may use different parts or default frequencies. Check the current MPS datasheets and test before production.
Updated: 2026-10-26 · Jasper
Parameters used on this page
| Parameter | Value | Source |
|---|---|---|
| VIN operating / absolute maximum | 4.5–28 V / 30 V | MP1584 Rev 1.0 p.2 |
| VOUT range | 0.8–25 V | p.2 |
| VFB | 0.776 / 0.8 / 0.824 V | p.3 |
| Feedback divider | Keep R2 under 40 kΩ; 40.2 kΩ is the typical value. The divider must absorb about 20 µA of bootstrap current at no load. | p.10 |
| Frequency | 100 kHz–1.5 MHz. RFREQ = 180000 / fs^1.1. 100 kΩ is about 900 kHz. | pp.1, 3, 9 |
| Minimum on-time | 100 ns, guaranteed by design | p.3 |
| Current limit | 4.0 A min / 4.7 A typ | p.3 |
| Inductor ripple guide | ΔIL about 30% of the maximum switch current limit. This page uses 30% of the 4.0 A minimum (1.2 A). | p.10 |
| EN | Rising 1.35 / 1.5 / 1.65 V, 300 mV hysteresis; off below 1.2 V; floating pulls up to about 3 V and turns on | pp.3–4, 8 |
| VIN UVLO | Rising 2.7 / 3.0 / 3.3 V, hysteresis 0.35 V (falling about 2.6 V) | pp.3, 8 |
| Thermal | θJA 50 °C/W (SOIC8E, JESD51-7 4-layer); thermal shutdown 150 °C; TJ −20 to 125 °C | pp.2–3 |
| Pinout (SOIC8E) | 1 SW, 2 EN, 3 COMP, 4 FB, 5 GND (exposed pad), 6 FREQ, 7 VIN, 8 BST | p.2 diagram, p.4 functions |
| Compensation examples | 3.3 V: L 6.8–10 µH, C2 22 µF, R3 68.1 kΩ, C3 220 pF. 5 V: L 15–22 µH, C2 22 µF, R3 100 kΩ, C3 150 pF. | Table 3, p.13 |
Worked examples
With R2 = 40.2 kΩ, 3.3 V uses 127 kΩ (3.327 V), 5 V uses 210 kΩ (4.979 V), and 12 V uses 562 kΩ (11.984 V). RFREQ is 193.4 kΩ at 500 kHz, 101.3 kΩ at 900 kHz, 90.2 kΩ at 1 MHz and 57.8 kΩ at 1.5 MHz. On-time for 24 V to 3.3 V is 137.5 ns at 1 MHz (pass) and 91.7 ns at 1.5 MHz (fail). At 500 kHz and a 1.2 A ripple target, 12 V to 5 V needs about 4.86 µH and 24 V to 5 V needs about 6.60 µH.
Pitfalls
- High VIN and low VOUT at high frequency hits the 100 ns minimum on-time. 24 V to 3.3 V at 1.5 MHz is 91.7 ns.
- EN floats on. Add a pull-down if you need on/off control.
- 28 V is the operating limit (30 V absolute maximum), so a surge on a 24 V rail can exceed it.
- R2 much larger than about 40 kΩ cannot absorb the about 20 µA bootstrap current at no load, so the output can drift up.
- Less than 3 V of headroom at light load starves the bootstrap capacitor. Keep VIN − VOUT above 3 V or add the external bootstrap diode.
- A 4.0 A minimum current limit does not mean 3 A continuous. Continuous current is set by heat at θJA 50 °C/W.
FAQ
Is the MP1584 discontinued?
No. MPS lists it as NRFND: still in production for existing customers, but not recommended for new designs. MPS points to the MP2338.
Is MP2338 a drop-in replacement for MP1584?
No. It uses a different package (SOT583) and pinout, a 0.5 V reference and a fixed 450 kHz frequency. Plan a new layout.
What resistor gives 5 V on an MP1584?
R1 = 210 kΩ with R2 = 40.2 kΩ gives 4.979 V.
How do I set MP1584 switching frequency?
RFREQ (kΩ) = 180000 / fs(kHz)^1.1. For example, about 193 kΩ for 500 kHz.
What inductor does the MP1584 need?
L = VOUT / (fs × ΔIL) × (1 − VOUT/VIN), with ΔIL about 30% of the switch current limit. Typical curves use 10 µH for 12 V to 5 V at 500 kHz. The compensation table lists 15–22 µH for 5 V.
Why does my MP1584 module not regulate?
At high frequency and low output, on-time can drop below 100 ns. At light load, VIN − VOUT under 3 V can starve the bootstrap capacitor.
Can MP1584 take 30 V input?
No. 28 V is the operating maximum. 30 V is the absolute maximum.
Is the MP1584 EN pin active high?
Yes. It turns on above about 1.5 V, turns off below 1.2 V, and floats high.
Related
Sources
- MPS, MP1584 datasheet Rev 1.0 (8/8/2011), NRFND version, retrieved 2026-10-26: https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP1584EN-LF-Z/document_id/204/
- MPS, MP1584 product page (status NRFND, alternative MP2338GTL), checked 2026-10-26: https://www.monolithicpower.com/en/products/mp1584.html
- MPS, MP2338 datasheet Rev 1.0 (12/11/2020), retrieved 2026-10-26: https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP2338GTL/document_id/9461/
- MPS, MP2338 product page (status Active), checked 2026-10-26: https://www.monolithicpower.com/en/products/mp2338.html
- Updated: 2026-10-26. Jasper.