Covers device behavior driving different load types including resistive, capacitive, and inductive, as well as specifics for each such as the VDS clamp for inductive turn-off, inrush handling for capacitive and bulb loads, and paralleling channels for higher current.
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Device Type |
Question |
Answer |
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HSS |
What happens to the output when switching off an inductive load (motor, solenoid, relay coil)? |
The inductor's stored energy drives the output pin negative (below GND) as current tries to continue flowing. TI's smart HSS devices include an internal active clamp that limits the negative output voltage swing, protecting the device. For very high inductance loads, verify the clamp energy rating against ½LI² stored energy. An external flyback diode adds no benefit if the internal clamp is rated for the load.
Related figure: SLVAG11, Figure 3-2 “Simplified Schematic and Timing Diagram of a High-Side Switch Driving an Inductive Load” shows the VDS clamp activating during turn-off and the resulting EHSD energy decay — ti.com/lit/pdf/slvag11. |
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HSS |
How do I drive incandescent bulb loads, and why do they behave differently from resistive loads? |
Incandescent bulb filaments have cold resistance 8–10× lower than hot resistance, causing very large inrush at turn-on. To handle:
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HSS |
Can I parallel two HSS channels to double the current capability? |
Yes, but current does not split exactly 50/50 due to Rds(on) variation between channels. Verify thermal balance under worst-case conditions. Both channels must be enabled simultaneously — staggered enable causes the first channel to carry full inrush momentarily. For HB/HC families, verify the sum of current sense outputs does not exceed the MCU ADC input range when both channels are active. Source: SLVA949: Paralleling Channels |
