Data Sheet

TB67S279FTG, TB67S289FTG, TB67S249FTG Application Note

2018-03-07

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Preliminary

12. Power Consumption of the IC

Power of the IC is consumed mainly by the transistor of the output block and by the internal

circuit, which includes the logic block.

P(total) = Power consumption of the IC

P(out) = Power consumption of the motor output block (MOSFET)

P(bias) = Power consumption of the internal circuit

P(total) = P(out) + P(bias)

(1) Power consumption of the motor output block

The motor output block consumes the power (P (out)) when the motor current flows in the

output MOSFET. In case of driving stepping motors, two channels of H-SW (A-ch and B-ch)

are controlled in parallel. Therefore, P (out) can be gained from below formula.

P(out) = Number of H-SW (= 2ch) × Motor current × Motor current × On resistance

(∵P = V × I = R(on) × I(out)

) ………. (1)

The power consumption above is gained under the condition that the motor current reaches

the configured peak value. Actually, since the IC performs PWM constant current control, the

peak current does not flow continuously. Hence, the average motor current is lower than the

configured value due to the current ripple (in the constant PWM drive) and the current decay

(in switching step resolution). Therefore, the power consumption above is only for reference.

Example) When motor current is 1 A, and the operation mode is full step resolution,

P(out) = 2 (ch) × 1.0 (A) × 1.0 (A) × 0.41 (Ω) = 0.82 (W)

(2) Power consumption of the internal circuit

The power for the internal circuit (P(bias)) including the logic block is continuously consumed

by applying VM voltage for the motor operation (standby release mode). It is calculated from

below formula.

P(bias) = Motor power supply voltage × Current consumption = VM × IM ………. (2)

Example) When motor power supply voltage of 24 V is applied,

P(bias) = VM × IM3, then 24 (V) × 0.006(A) = 0.144 (W)

From above formula, the rough value of this IC power consumption is as follows;

P(total) = P(out) + P(bias) = 0.82 + 0.144 = 0.964 (W)

The power consumption of the standby mode, which reduces bias current of the internal circuit,

can be calculated from the formula (2) by substituting IM1 (standby mode) for IM current

consumption.

P(bias) = 24 (V) × 0.002 (A) = 0.048 (W)