CSD88584Q5DC Datasheet, PDF (13/24 Pages) Texas Instruments – 40-V Half-Bridge NexFET Power Block

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CSD88584Q5DC
SLPS598 – MAY 2017
6.3 Power Loss Curves
CSD88584Q5DC was designed to operate up to 7-cell Li-Ion battery voltage applications ranging from 18 V to 32
V, typical 24 V. For 8s, input voltages between 32 V to 36 V, RC snubbers are required for each switch-node U,
V, and W. To reduce ringing, refer to the Electrical Performance section. In an effort to simplify the design
process, Texas Instruments has provided measured power loss performance curves over a variety of typical
conditions.
Figure 1 plots the CSD88584Q5DC power loss as a function of load current. The measured power loss includes
both input conversion loss and gate drive loss.
Equation 1 is used to generate the power loss curve:
Power loss (W) = (V_IN × I_{IN_SHUNT}) + (V_DD × I_{DD_SHUNT}) – (V_{SW_AVG} × I_OUT)
(1)
The power loss measurements were made on the circuit shown in Figure 19, power block devices for legs U and
V, PB1 and PB2 were disabled by shorting the CSD88584Q5DC high-side and low-side FETs gate-to-source
terminals. Current shunt Iin_shunt provides Input current and Idd_SHUNT provides driver supply current
measurements. The winding current is measured from the DC load. An averaging circuit provides switch node W
equivalent RMS voltage.
Iin_SHUNT
Cin1
0
Vin
Cin2
0 GH1
SH1
PB1
Vin
PB2
GH2
SH2
Vsw1 U
GL1
GL2
Vin
Idd_SHUNT
Vdd
Vdd
0
Vsw2 V
0
U 1A
1
2
HI
GATE
DRIVER
LI
PB3
Vin
GH3
SH3
Vsw3
GL3
W
Lout
DCR
PGND
PGND
0
0
0
0
0
0
PWM
PGND
0
0
AVERAGING
CIRCUIT
Iout
LOAD
0
AVERAGE
SWITCH NODE
Vsw_AVG
Copyright © 2017, Texas Instruments Incorporated
Figure 19. Power Loss Test Circuit
The RMS current on the CSD88584Q5DC device depends on the motor winding current. For trapezoidal control,
the MOSFET RMS current is calculated using Equation 2.
I_RMS = I_OUT × √2
(2)
Taking into consideration system tolerances with the current measurement scheme, the inverter design needs to
withstand a 20% overload current.
Table 1. RMS and Overload Current Calculations
Winding RMS Current (A)
30
40
50
CSD88584Q5DC I_RMS (A)
42
56
70
Overload 120% × I_RMS (A)
51
68
85
Copyright © 2017, Texas Instruments Incorporated
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