ZHCSGC2F June 2017 – January 2019 UCC5310 , UCC5320 , UCC5350 , UCC5390
PRODUCTION DATA.
The total loss, P_{G}, in the gate-driver subsystem includes the power losses (P_{GD}) of the UCC53x0 device and the power losses in the peripheral circuitry, such as the external gate-drive resistor.
The P_{GD} value is the key power loss which determines the thermal safety-related limits of the UCC53x0 device, and it can be estimated by calculating losses from several components.
The first component is the static power loss, P_{GDQ}, which includes quiescent power loss on the driver as well as driver self-power consumption when operating with a certain switching frequency. The P_{GDQ} parameter is measured on the bench with no load connected to the OUT or OUTH and OUTL pins at a given V_{CC1}, V_{CC2}, switching frequency, and ambient temperature. In this example, V_{CC1} is 3.3V and V_{CC2} is 15 V. The current on each power supply, with PWM switching from 0 V to 3.3 V at 10 kHz, is measured to be I_{CC1} = 1.67 mA and I_{CC2} = 1.11 mA. Therefore, use Equation 5 to calculate P_{GDQ}.
The second component is the switching operation loss, P_{GDO}, with a given load capacitance which the driver charges and discharges the load during each switching cycle. Use Equation 6 to calculate the total dynamic loss from load switching, P_{GSW}.
where
So, for this example application the total dynamic loss from load switching is approximately 18 mW as calculated in Equation 7.
Q_{G} represents the total gate charge of the power transistor switching 520 V at 50 A, and is subject to change with different testing conditions. The UCC5320S gate-driver loss on the output stage, P_{GDO}, is part of P_{GSW}. P_{GDO} is equal to P_{GSW} if the external gate-driver resistance and power-transistor internal resistance are 0 Ω, and all the gate driver-loss will be dissipated inside the UCC5320S. If an external turn-on and turn-off resistance exists, the total loss is distributed between the gate driver pull-up/down resistance, external gate resistance, and power-transistor internal resistance. Importantly, the pull-up/down resistance is a linear and fixed resistance if the source/sink current is not saturated to 4.3 A/4.4 A, however, it will be non-linear if the source/sink current is saturated. Therefore, P_{GDO} is different in these two scenarios.
Case 1 - Linear Pull-Up/Down Resistor:
In this design example, all the predicted source and sink currents are less than 4.3 A and 4.4 A, therefore, use Equation 9 to estimate the UCC53x0 gate-driver loss.
Case 2 - Nonlinear Pull-Up/Down Resistor:
where
For some scenarios, if only one of the pullup or pulldown circuits is saturated and another one is not, the P_{GDO} is a combination of case 1 and case 2, and the equations can be easily identified for the pullup and pulldown based on this discussion.
Use Equation 11 to calculate the total gate-driver loss dissipated in the UCC53x0 gate driver, P_{GD}.