4 Design of Gate Ringing Issues

LM5125A-Q1 and LM5126A-Q1 are widely used in automotive external amplifiers. The test follows the design scenarios of the application as a reference, as the main test setup in Table 4-1

Based on the original design, 1nF, 1.5nF, 2.2nF, and 3.3nF capacitors connected in parallel with Q1 were tested, and gate ringing tests were conducted on the turn-on and turn-off processes of the high-side MOSFET.

1. Original Design Test:
   Figure 4-1 Original Design Test Results (HS ON/LS OFF (Left), HS OFF/LS ON (Right))
2. HO+1nf:
   Figure 4-2 HO+1nf Test Results: HS ON/LS OFF (Left), HS OFF/LS ON (Right)
3. HO+1.5nf:
   Figure 4-3 HO+1.5nf Test Results: HS ON/LS OFF (Left), HS OFF/LS ON (Right)
4. HO+2.2nf:
   Figure 4-4 HO+2.2nf Test Results: HS ON/LS OFF (Left), HS OFF/LS ON (Right)
5. HO+3.3nf:

The test results are summarized in Table 4-2

Therefore, considering the additional losses and the impact on switching speeds, it is calculated by

External 1.5nF only increases the HO gate driver loss.

TI recommends incorporating a provision for this capacitor during the design phase; this facilitates debugging and eliminates risk if issues such as gate ringing arise. of HO+1.5nF as shown in Figure 4-6

TI recommends another design.

As shown in Figure 4-7, an alternative design approach involves incorporating a PNP transistor on the drive side of the high-side switch. This design serves to enhance noise immunity and prevent spurious turn-on. When the HO output is in the OFF state, the current is coupled to GND through the PNP transistor, thereby preventing the buildup of a gate-source voltage (Ugs). This common-base PNP pull-down configuration effectively suppresses coupled interference, thereby preventing the inadvertent activation of the HO output.