ZHCSOX6C September 2021 – December 2022 UCC14240-Q1
PRODUCTION DATA
The UCC14240-Q1 device creates an isolated output VDD-VEE as its main output. The device also creates a second output COM-VEE, using VDD-VEE as its power source. Because both outputs are isolated from the input, and sharing VEE as the common reference point, the UCC14240-Q1 outputs can be configured as dual-output two-positive, dual-output two-negative, or dual-output one-positive and one-negative. UCC14240-Q1 output can also be used as a single positive output or single negative output.
When the module is configured as dual-output, one-positive output, one-negative output; it is very important to properly select the output capacitor ratios COUT2 and COUT3 to optimize the regulation and avoid causing an over-voltage or under-voltage fault.
| CAPACITOR | VALUE (µF) | NOTES |
|---|---|---|
| CIN | 10 + 0.1 | Place a 10-μF and a 0.1-μF high-frequency decoupling capacitor in parallel close to VIN pins. A capacitance greater than 10uF can be used to reduce the voltage ripple when the series impedance from the voltage source to the VIN pins is large. Optionally, connect a 330pF 0402 size high-frequency bypass ceramic capacitor close to analog VIN PIN 6 and GNDP PIN 5 when the input voltage ripple is large enough to interfere with the internal input voltage sense signal and the normal startup operation. For extreme input ripple voltage cases, connect a 4.75-ohm filter resistor to power input, PIN7, and connect a 10-μF ceramic capacitor from analog VIN PIN 6, to power analog GNDP. In most cases, the RC input filter is not needed. If the filter resistor is not placed, make sure both PIN 6 and PIN 7 are connected to input voltage. |
| COUT1 | 2.2 + 0.1 | Add a 2.2-μF and a 0.1-μF capacitor for high-frequency decoupling of (VDD – VEE). Place close to the VDD and VEE pins. A capacitance greater than 2.2uF can be used to reduce the output voltage ripple. |
| COUT2 | See below | Bulk charge, decoupling output capacitors are required at the gate driver pins. The COUT2 and COUT3 capacitance ratio is important to optimize the dual output voltage divider accuracy during charge or discharge switching cycles. |
| COUT3 | See below |
The selection of COUT2 and COUT3 is based on the gate charge requirement for the gate driver load, the charge balancing during the start-up, and the expected maximum current loading.
During the startup, the ratio between COUT2 and COUT3 must be equal to the ratio between (COM−VEE) and (VDD−COM) and offset by the loading current from VDD-COM and COM-VEE, to allow both COM to VEE and VDD to VEE voltages reaches steady state at the same time, as shown in Equation 1.
First calculate the COUT2 value based on the Gate charge of the power device QG_Total, whether IGBT or SiC power MOSFET, and the percent of voltage droop wanted during the turn-on of the gate with respect to the positive gate voltage applied, VDD to COM.
QG_Total is the total gate charge of the power switch
Then calculate the COUT3 value based on the output voltage ratios, the load current expected, and the variation of the output capacitors.
where the load IVDD-COM and ICOM-VEE are the load currents respectively, and the IMAX_POWER is the SOA Maximum Power (PMAX_SOA) divided by the VVDD-VEE output voltage.
where
I(VDD-COM) is the total current from VDD to COM, excluding average gate drive current.
I(COM-VEE) is the total current from COM to VEE, excluding average gate drive current.
and
The approximate PMAX value can be extracted from the provided SOA curves at the respective ambient temperature.
Calculate COUT3 using worst case capacitor values based on expected variation, COUT3_maximum, and COUT3_Minimum . This action makes sure the capacitor ratio tends to push the COM-VEE voltage to a slightly lower value than the target regulation value during startup.
COUT2 and COUT3 are the total capacitance on the VDD and VEE outputs. They include the capacitors from both the isolated bias supply and the gate driver circuit.
The sizes of COUT2 and COUT3 are determined by the gate driver load gate charge and ripple voltage requirement. COUT1 can then be used to reduce the total ripple voltage and to soften the start-up time.