Rohm Thermal Calculator

Simple calculator for stepper motor driver junction temperature



The program provided on this page is intended for the thermal design of current control PWM drive for 2-phase stepper motor drivers. By using this calculation tool, the chip junction temperature can be easily determined with different usage environments, packages, and board types, by taking into consideration the power consumption of each operating region (e.g. PWM ON/OFF, PWM/phase switching) - in combination with Full/Half Excitation and Slow/Fast Decay Modes.

This program allows equipment designers to analyze the thermal design of a wide variety of applications.

When in use, approximation of the current waveform variation during phase switching (based on motor operation) may vary, along with the PWM switching speed - depending on the motor characteristics and usage conditions. Therefore, please note that deviations may occur in the calculated results and actual temperature.

Please refer to the application notes containing detailed tutorials.


Device Input Values
RonH =  
RonL =  
VfH =  
VfL =  
Icc =  
Motor Input Values
Em =  
Rm =  
Lm =  
Application Input Values
Vcc =  
Ipk =  
fPWM =  
fCLK =  
Rs =  


Power Dissipation Results
Pcpw 
Pcq 
Pc 
Thermal Data Input and Results
Ta =    °C
Θj-a =    °C/W

Tj 

Calculate History
Version:1.02
Glossary Description
High Side Drian-Source On Resistence Equivalent resistance value when the power MOSFET between the IC output block motor output terminal and output block power supply is ON.
Low Side Drian-Source On Resistence Equivalent resistance value when the power MOSFET between the IC output block motor output terminal and output block Ground is ON.
High Side Diode Voltage When the power MOSFET between the IC output block motor output terminal and output block power supply is OFF, there is a diode that allows current to flow from the output terminal to the output power supply, and this current flow generates an equivalent voltage.
Low Side Diode Voltage When the power MOSFET between the IC output block motor output terminal and output block Ground is OFF, there is a diode that allows current to flow between the output Ground and output terminal, and this current flow generates and equivalent voltage.
Quiescent Current DC circuit current value of the small-signal block
Generated Voltage Generated voltage corresponding to the rotational speed when the motor is in operation
Motor Resistence Equivalent resistance of the motor per phase
Motor Inductance Equivalent inductance of the motor per phase
Supply Voltage Power supply voltage value
Peak Current Current flowing to the motor is increased during PWM operation, then PWM operation is stopped at the peak current value and current regeneration operation is initiated.
PWM Frequency PWM frequency set via external resistor and capacitor
Step Frequency Phase switching frequency. For CLK-IN input operation, the frequency is input at the CLK-IN terminal, and for parallel input operation, it's the inverse of the period for changing the state between the parallel inputs
Sensing Resistance Detection resistance when converting the output current to voltage via resistor
Decay Type Current flowing to the motor is increased during PWM operation, then PWM operation is stopped at the peak current value and current regeneration operation is initiated. Current regeneration is referred to as decay, and in Fast mode the current is quickly attenuated, while in Slow mode the attenuation is gradual. Mix mode combines the two modes. Calculation supports both Fast and Slow modes.
Stepping Sequence By changing the way of supplying current to the windings, stepper motors can vary the rotational characteristics. When current is supplied, a magnetic field is generated at the coil. This is referred to as 'excitation.' 2-phase stepper motors can be divided into the following four classifications.
1-Phase Excitation:
Single-phase current flow to the windings only. Positional accuracy is good, but damping motion tends to remain. Generally not used.
2-Phase Excitation (Full Step):
2-phase current flow. Achieves twice the output torque compared with single-phase excitation.
1-2-Phase Excitation (Half Step):
Current flows by switching alternately between single- and dual-phase. Half-step angles are possible in the case of 1-/2-phase excitation, enabling smooth rotation.
Microstep Drive:
Instead of simply switching the current to the windings ON/OFF, this method varies the current ratio of the two windings to obtain a more precise step angle. Step angles of 1/4, 1/8, and 1/16 are possible. Calculation supports 2-phase and 1-2-phase excitation.
Ambient Temperature It is the temperature of the environment in which your use of IC.
Thermal Resisitance Juncttion to Ambient Thermal resistance value of the entire circuit, including the package and mounting substrate (under usage conditions), and the amount of rise in the junction temperature of the IC chip per 1W (expressed in °C)