8.4.2.2 DT Pin Left Open or Connected to a Programming Resistor between DT and GND Pins

If the DT pin is left open, the dead time duration (t_DT) is set to <15 ns. One can program t_DT by placing a resistor, R_DT, between the DT pin and GND. The appropriate R_DT value can be determined from from Equation 1, where R_DT is in kΩ and t_DT is in ns:

Equation 1.

The steady state voltage at DT pin is around 0.8 V, and the DT pin current will be less than 10uA when R_DT=100kΩ. Therefore, It is recommended to parallel a ceramic capacitor, 2.2nF or above, close to the chip with R_DT to achieve better noise immunity and better deadtime matching between two channels, especially when the dead time is larger than 300ns. The major consideration is that the current through the R_DT is used to set the dead time, and this current decreases as R_DT increases.

An input signal’s falling edge activates the programmed dead time for the other signal. The output signals’ dead time is always set to the longer of either the driver’s programmed dead time or the input signal’s own dead time. If both inputs are high simultaneously, both outputs will immediately be set low. This feature is used to prevent shoot-through, and it doesn’t affect the programmed dead time setting for normal operation. Various driver dead time logic operating conditions are illustrated and explained in Figure 37:

Figure 37. Input and Output Logic Relationship With Input Signals

Condition A: INB goes low, INA goes high. INB sets OUTB low immediately and assigns the programmed dead time to OUTA. OUTA is allowed to go high after the programmed dead time.

Condition B: INB goes high, INA goes low. Now INA sets OUTA low immediately and assigns the programmed dead time to OUTB. OUTB is allowed to go high after the programmed dead time.

Condition C: INB goes low, INA is still low. INB sets OUTB low immediately and assigns the programmed dead time for OUTA. In this case, the input signal’s own dead time is longer than the programmed dead time. Thus, when INA goes high, it immediately sets OUTA high.

Condition D: INA goes low, INB is still low. INA sets OUTA low immediately and assigns the programmed dead time to OUTB. INB’s own dead time is longer than the programmed dead time. Thus, when INB goes high, it immediately sets OUTB high.

Condition E: INA goes high, while INB and OUTB are still high. To avoid overshoot, INA immediately pulls OUTB low and keeps OUTA low. After some time OUTB goes low and assigns the programmed dead time to OUTA. OUTB is already low. After the programmed dead time, OUTA is allowed to go high.

Condition F: INB goes high, while INA and OUTA are still high. To avoid overshoot, INB immediately pulls OUTA low and keeps OUTB low. After some time OUTA goes low and assigns the programmed dead time to OUTB. OUTA is already low. After the programmed dead time, OUTB is allowed to go high.