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SNVSCM3 June 2024 LM5171

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6.4.1 Dynamic Dead Time Adjustment

In addition to a fixed dead time programming by R_DT, the dead time can be dynamically adjusted either by applying an analog voltage or a PWM signal as shown in Figure 6-29. Varying the analog voltage or the duty ratio of the PWM signal adjusts the DT programming. For analog adjustment, a single stage RC filter is recommended to filter out any possible noise. For PWM adjustment, a two-stage RC filter is recommended to minimize the ripple voltage resulted on the DT pin.

Figure 6-29 Dynamic Dead Time Adjustment a

Figure 6-30 Dynamic Dead Time Adjustment b

When an analog voltage is applied, the resulted dead time is determined by Equation 18:

Equation 18.

t_{D T} (V_{A D J}) = {(\frac{1}{R_{D T}} + \frac{1}{R_{A D J 1} + R_{A J D 2}} - \frac{0.8 \times V_{A D J}}{R_{A D J 1} + R_{A J D 2}})}^{- 1} \times 2.625 \frac{n s}{k Ω}

where

V_ADJ is the analog voltage used to adjust the dead time

When a PWM signal is applied, the resulted dead time is determined by Equation 19:

Equation 19.

t_{D T} (D_{A D J}) = {(\frac{1}{R_{D T}} + \frac{1}{R_{A D J 1} + R_{A J D 2} + R_{A J D 3}} - \frac{0.8 \times [(V_{H I} - V_{L O}) \times D_{A D J} + V_{L O}]}{R_{A D J 1} + R_{A J D 2} + R_{A J D 3}})}^{- 1} \times 2.625 \frac{n s}{k Ω}

where

V_HI and V_LO are the high and low voltage levels of the PWM signal, respectively,
D_ADJ is the duty factor of the PWM signal.

Note that in dynamic dead time programming, to equivalent impedance at the DT /SD pin seen by the IC must be greater than 5 kΩ to prevent unintended shutdown latch. See Section 6.3.12 for details.

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6.4.1 Dynamic Dead Time Adjustment