
TB62218FNG
2010-10-07
13
IC Power Consumption
The power consumed by the TB62218FNG is approximately the sum of the following two: 1) the power consumed by
the output transistors, and 2) the power consumed by the digital logic and pre-drivers.
The power consumed by the output transistors is calculated, using the RON (D-S) value of 1.0 Ω.
Whether in Charge, Fast Decay or Slow Decay mode, two of the four transistors comprising each H-bridge
contribute to its power consumption at a given time.
Thus the power consumed by each H-bridge is given by:
P (out)
= IOUT (A) × VDS (V) = 2 × IOUT2 × RON .........................................(1)
In two-phase excitation mode (in which two phases have a phase difference of 90°), the average
power consumption in the output transistors is calculated as follows:
RON = 1.0 Ω (@2.0 A)
IOUT (Peak) = 1.0 A
VM = 24 V
P (out)
= 2Hsw × 1.02 (A) × 1.0 (Ω) = 2.0 (W)................................................(2)
The power consumption in the IM domain is calculated separately for normal operation and standby
modes:
Normal operation mode: I (IM3) = 5.0 mA (typ.)
Standby mode: I (IM1) = 2.0 mA (typ.)
The current consumed in the digital logic portion of the TB62218FNG is indicated as IMx. The
digital logic operates off a voltage regulator that is internally connected to the VM power supply. It
consists of the digital logic connected to VM (24 V) and the network affected by the switching of the
output transistors. The total power consumed by IMx can be estimated as:
P (IM) = 24 (V) × 0.005 (A) = 0.12 (W)...........................................................(3)
Hence, the total power consumption of the TB62218FNG is:
P
= P (out) + P (IM) = 2.12 (W)
The standby power consumption is given by:
P (Standby)
, P (out) = 24 (V) × 0.002 (A) = 0.048 (W)
Board design should be fully verified, taking thermal dissipation into consideration.