Thermal Design

<Hybrid IC Average Internal Power Loss Pd>

The main elements internal to this hybrid IC with large average power losses are the current control devices, the

regenerative current diodes, and the current detection resistor. Since sine wave drive is used, the average power loss

during microstepping drive can be approximated by applying a waveform factor of 0.64 to the square wave loss during 2

phase excitation.

The losses in the various excitation modes are as follows.

fclock

2 phase excitation

2

2

fclock

1-2 phase excitation

4

4

fclock

W1-2 phase excitation

8

8

fclock

2W1-2 phase excitation

16

16

fclock

4W1-2 phase excitation

16

16

Here, t1 and t3 can be determined from the same formulas for all excitation methods.

–L

R + 0.35

–L

t1 = ———— ·

t3 = —— ·

n (——————————)

R + 0.35

R

However, the formula for t2 differs with the excitation method.

2

3

2 phase excitation

t2 = ——— – (t1 +t3)

1-2 phase excitation

t2 = ——— – t1

fclock

fclock

7

15

W1-2 phase excitation

t2 = ——— – t1

2W1-2 phase excitation

t2 = ——— – t1

fclock

4W1-2 phase excitation

fclock

Motor Phase Current Model Figure (2 Phase Excitation)

fclock: CLK input frequency (Hz)

Vsat: The voltage drop of the power MOSFET and the current detection resistor (V)

Vdf: The voltage drop of the body diode and the current detection resistor (V)

t1: Phase current rise time (s)

t2: Constant-current operating time (s)

L: Motor inductance (H)

t3: Phase switching current regeneration time (s)

R: Motor winding resistance (W)

No. 6507-14/17

STK672-080

t3

t1

t2

IOH

A13270