What does RDS mean in the MOSFET Rds(on) vs Temperature formula?

RDS is Rds(on) at operating temperature (Ω).

MOSFET Rds(on) vs Temperature

Q: How do you calculate MOSFET Rds(on) vs Temperature?

Use the formula RDS(T) = RDS_ref × (1 + tc × ΔT). MOSFET on-resistance increases significantly with temperature due to decreased carrier mobility in the silicon channel. Enter the values you know in the calculator above and it solves for the remaining variable.

Q: What is the formula for MOSFET Rds(on) vs Temperature?

The MOSFET Rds(on) vs Temperature formula is RDS(T) = RDS_ref × (1 + tc × ΔT), where RDS—Rds(on) at operating temperature (Ω); RDS_ref—Rds(on) at reference temperature, usually 25°C (Ω); tc—Temperature coefficient (typically 0.004 to 0.008 per °C for Si); ΔT—Temperature rise from reference (°C).

RDS(T) = RDS_ref × (1 + tc × ΔT)

Quick answer

This calculator solves RDS(T) = RDS_ref × (1 + tc × ΔT) for Rds(on) at Temp. With Rds(on) Reference 110 mΩ, Temp Coefficient 0.5, Temperature Change 50 °C, the result is 2.86 Ω. It solves in 2 directions, so you can enter the values you have and get the one you need.

Calculator

Rds(on) Reference

Temp Coefficient

Temperature Change

Rds(on) at Temp (mΩ)

—

Formula

RDS(T) = RDS_ref × (1 + tc × ΔT)

Description

MOSFET on-resistance increases significantly with temperature due to decreased carrier mobility in the silicon channel. This positive temperature coefficient is actually beneficial for current sharing when MOSFETs are paralleled, as the hotter device automatically takes less current. However, it means that the room-temperature Rds(on) from the datasheet summary significantly underestimates the actual resistance at operating junction temperatures. A typical silicon MOSFET's Rds(on) approximately doubles from 25°C to 125°C.

Variables

RDS — Rds(on) at operating temperature (Ω)
RDS_ref — Rds(on) at reference temperature, usually 25°C (Ω)
tc — Temperature coefficient (typically 0.004 to 0.008 per °C for Si)
ΔT — Temperature rise from reference (°C)

Practical Notes

Use the Rds(on) vs temperature graph from the datasheet for accurate values. GaN FETs have a lower temperature coefficient than silicon. SiC MOSFETs have nearly flat Rds(on) vs temperature. Always calculate conduction losses using the hot Rds(on), not the 25°C value. The linearized tc model is an approximation; the actual relationship is slightly nonlinear.

Symbols and units

Symbol	Meaning	Default unit	Accepted units
RDS	Rds(on) at Temp	mΩ	mΩ, Ω, kΩ, MΩ
RDS_ref	Rds(on) Reference	mΩ	mΩ, Ω, kΩ, MΩ
tc	Temp Coefficient	—	—
dT	Temperature Change	°C	°C

Step by step

1. What you know: Rds(on) Reference 110 mΩ, Temp Coefficient 0.5, Temperature Change 50 °C
2. The relation: RDS(T) = RDS_ref × (1 + tc × ΔT)
3. Substitute: RDS_ref = 110 mΩ, tc = 0.5, dT = 50 °C
4. Result: Rds(on) at Temp = 2.86 Ω

Nearest standard component values

Series	Nearest value	Error
E12	2.7 Ω	5.6%
E24	3 Ω	4.9%

Worked examples

Minimum range

Given: Rds(on) Reference 0.22 mΩ, Temp Coefficient 0.025, Temperature Change 2.5 °C

Result: Rds(on) at Temp = 0.2338 mΩ

Low range

Given: Rds(on) Reference 2.2 mΩ, Temp Coefficient 0.25, Temperature Change 25 °C

Result: Rds(on) at Temp = 15.95 mΩ

Typical

Given: Rds(on) Reference 110 mΩ, Temp Coefficient 0.5, Temperature Change 50 °C

Result: Rds(on) at Temp = 2.86 Ω

High range

Given: Rds(on) Reference 1.1 Ω, Temp Coefficient 0.8, Temperature Change 85 °C

Result: Rds(on) at Temp = 75.9 Ω

Maximum range

Given: Rds(on) Reference 11 Ω, Temp Coefficient 8, Temperature Change 850 °C

Result: Rds(on) at Temp = 74.81 kΩ

Solving for each variable

Solve for Rds(on) at Temp

Rds(on) Reference 0.22 mΩ, Temp Coefficient 0.025, Temperature Change 2.5 °C → 0.2338 mΩ

Solve for Rds(on) Reference

Rds(on) at Temp 0.1 mΩ, Temp Coefficient 0.025, Temperature Change 2.5 °C → 0.09412 mΩ

How Rds(on) at Temp changes with Rds(on) Reference

Rds(on) Reference (input)	Rds(on) at Temp (result)
11 mΩ	0.286 Ω
27.5 mΩ	0.715 Ω
55 mΩ	1.43 Ω
82.5 mΩ	2.145 Ω
110 mΩ	2.86 Ω
0.165 Ω	4.29 Ω
0.22 Ω	5.72 Ω
0.44 Ω	11.44 Ω
0.77 Ω	20.02 Ω
1.1 Ω	28.6 Ω

The same result in other units

Unit	Value
mΩ	2860
Ω	2.86
kΩ	0.00286

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Frequently asked questions

How do you calculate MOSFET Rds(on) vs Temperature?

Use RDS(T) = RDS_ref × (1 + tc × ΔT). With Rds(on) Reference 110 mΩ, Temp Coefficient 0.5, Temperature Change 50 °C, Rds(on) at Temp works out to 2.86 Ω.

What is the formula for MOSFET Rds(on) vs Temperature?

The formula is RDS(T) = RDS_ref × (1 + tc × ΔT). MOSFET on-resistance increases significantly with temperature due to decreased carrier mobility in the silicon channel.

How do you find Rds(on) Reference when you know the other values?

Rearrange for Rds(on) Reference: with Rds(on) at Temp 0.1 mΩ, Temp Coefficient 0.025, Temperature Change 2.5 °C, Rds(on) Reference is 0.09412 mΩ.

What units does MOSFET Rds(on) vs Temperature use?

Rds(on) at Temp is shown in mΩ, Ω, kΩ. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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