TLE4727 Datasheet, PDF (18/22 Pages) Siemens Semiconductor Group – 2-Phase Stepper-Motor Driver

TLE 4727
Calculation of Power Dissipation
The total power dissipation P_tot is made up of
saturation losses P_sat (transistor saturation voltage and diode forward voltages),
quiescent losses P_q (quiescent current times supply voltage) and
switching losses P_s (turn-ON / turn-OFF operations).
The following equations give the power dissipation for chopper operation without phase
reversal. This is the worst case, because full current flows for the entire time and
switching losses occur in addition.
P_tot = 2 × P_sat + P_q + 2 × P_s
where
P_sat ≅ I_N {V_satI × d + V_Fu (1 – d) + V_satuC × d + V_satuD (1 – d)}
P_q = I_q × V_S
P_S
≅
V_----S-
T



i_--D-----×_---2-t_{--D----O---N-}
+
(_---i_{--D----+-----}i_--R4---)_---×_-----t_--O----N-
+
-^I--^N-
2
(t_DOFF
+
t_OFF)



I_N = nominal current (mean value)
I_q = quiescent current
i_D = reverse current during turn-ON delay
i_R = peak reverse current
t_p = conducting time of chopper transistor
t_ON = turn-ON time
t_OFF = turn-OFF time
t_DON = turn-ON delay
t_DOFF = turn-OFF delay
T = cycle duration
d = duty cycle t_p / T
V_satl = saturation voltage of sink transistor (T_X3, T_X4)
V_satuC = saturation voltage of source transistor (T_X1, T_X2) during charge cycle
V_satuD = saturation voltage of source transistor (T_X1, T_X2) during discharge cycle
V_Fu = forward voltage of free-wheeling diode (D_X1, D_X2)
V_S = supply voltage
Semiconductor Group
18
1998-12-16