
5
FIGURE 5. SHUT-DOWN (VSD) TIMING RELATIONSHIPS
1
0
1
0
1
0
1
0
1
0
1
0
1
0
H
Z
L
H
Z
L
H
Z
L
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
tSd
V Sd
V OA
H
Z
L
1
0
V UA
V UB
V UC
V LA
V LB
V LC
V Sd
V OA
V OB
V OC
CHARGE PUMP
The PWR-82341 has an internal charge pump circuit to generate
the drive voltage for the high side N-channel MOSFETs (see
Figure 4). The charge pump uses an oscillator to charge an
external charge pump capacitor, Cc, from the Vcc supply. This
oscillator will pump the voltage at the +cap pin (48) of the hybrid
higher than Vcc. The hybrid high side drivers use this voltage to
ensure proper gate drive.
An external 1 F, 20% capacitor (Cc) is required between the
+cap pin and the -cap pin (50) on the hybri d. If a polarized
capacitor is used, the positive terminal must be connected to the
+cap pin. The voltage rating of Cc must be 2x the maximum
value of Vcc.
PWR-82341 POWER DISSIPATION (SEE FIGURE 7)
There are three major contributors to power dissipation in the
motor driver: conduction losses, switching losses, and intrinsic
diode losses.
VCC = +28 V (Bus Voltage)
IoA = 3 A, IOB = 7 A (see FIGURE 7)
ton = 20 s, T = 40 s (period) (see FIGURE 7)
Ron = 0.13
(on-resistance, see TABLE 2, Io = 5 A, Tc= +25°C)
ts1 = 325 ns, ts2 = 325 ns (see FIGURE 7)
fo = 25 kHz (switching frequency)
VF is an intrinsic diode forward voltage, TABLE 2, Io = 5 A
1. Conduction Losses (PC)
Pc = ( Imotor rms)2 x Ron
I motor rms=
IOB - IOB (IOB - IOA) +
(IOB - IOA)
ton
2
3
T
Pc = (3.63 A)2 x (0.13
)
Pc = 1.71 Watts
2. Switching Losses (PS)
Ps = [Vcc (IOA (ts1) +IOB (ts2) ) fo] / 2
Ps = [28 V (3 A (325 ns) +7 A (325 ns) ) 25 kHz] / 2
Ps = 1.14 Watts
3. Intrinsic Diode Losses (Pd)
Pd= Id (avg) x Vd (avg)
Id(avg) = [(IOB + IOA) / 2] / 2 = [(7 A +3 A) / 2] / 2 = 2.5 A
Pd = 2.5 A x 1.25 V
Pd = 3.125 Watts
TRANSISTOR POWER DISSIPATION (PQ)
To calculate the maximum power dissipation of the output tran-
sistor as a function of the case temperature use the following
equation. (Reference FIGURE 9 to ensure you don’t exceed the
maximum allowable power dissipation of each transistor.
PQ = Pc + Ps + Pd
TOTAL HYBRID POWER DISSIPATION (P
TOTAL)
To calculate Total Power dissipated in the hybrid use:
6
P
TOTAL=
ΣΣ [PQi] where i = each transistor
i=1
I motor rms=
7A - 7A (7A - 3A) +
(7A - 3A)
20us
2
3
40us