SNVSC75 Data sheet

SNVSC75B April 2023 – September 2025 LM5171-Q1

PRODUCTION DATA

8.4 Dynamic Dead Time Adjustment

In addition to a fixed dead time programming by R_DT, the dead time is dynamically adjusted either by applying an analog voltage or a PWM signal as shown in Figure 8-10. 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.

LM5171-Q1 Dynamic Dead Time Adjustment a

Figure 8-10 Dynamic Dead Time Adjustment a

LM5171-Q1 Dynamic Dead Time Adjustment b

Figure 8-11 Dynamic Dead Time Adjustment b

When an analog voltage is applied, the resulted dead time is determined by Equation 73:

Equation 73.

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 74:

Equation 74.

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, the equivalent impedance at the DT /SD pin seen by the IC needs to be greater than 5 kΩ to prevent unintended shutdown latch. See Section 6.3.13 for details.