米6体育平台手机版

SLVSHS7 October 2024 TPSI31P1-Q1

ADVANCE INFORMATION

封装选项

机械数据 (封装 | 引脚)

DVX|16

散热焊盘机械数据 (封装 | 引脚)

订购信息

slvshs7_oa

7.2.2 Detailed Design Procedure

The battery voltage (V_BAT), link capacitance (C_{DC_LINK}), along with the target pre-charge time determines the average charging current (I_AVG) required. This may be computed as follows:

Equation 1.

I_{A V G} \geq \frac{C_{D C_{L I N K}} \times V_{B A T}}{t_{C H A R G E}} = \frac{2 m F \times 800 V}{800 m s} = 2 A

The average current is defined as:

Equation 2.

I_{A V G} = \frac{I_{P E A K} + I_{M I N}}{2}

The peak current, I_PEAK, represents the maximum current through the inductor, and is defined by:

Equation 3.

I_{P E A K} = \frac{V_{R E F +}}{R_{S E N S E}}

Similarly, the minimum current, I_MIN, represents the minimum current through the inductor, and is defined by:

Equation 4.

I_{M I N} = \frac{V_{R E F -}}{R_{S E N S E}}

Therefore, to find the shunt resistor, R_SENSE, required to properly set the inductor current, the following equation can be used:

Equation 5.

R_{S E N S E} = \frac{{V_{R E F +} + V}_{R E F -}}{2 I_{A V G}} = \frac{1.23 V + 0.16 V}{2 \times 2 A} = 348 m Ω

For this design, R_SENSE was selected as 300mΩ.

The peak inductor current is computed as:

Equation 6.

I_{P E A K} = \frac{1.23 V}{300 m Ω} = 4.1 A

The minimum inductor current is computed as:

Equation 7.

I_{M I N} = \frac{0.16 V}{300 m Ω} = 0.53 A

The average inductor current is computed as:

Equation 8.

I_{A V G} = \frac{I_{P E A K} + I_{M I N}}{2} = \frac{4.1 A + 0.53 A}{2} = 2.32 A

During pre-charge, due to the hysteretic control, the switching frequency of the FET changes over time as the voltage on the link capacitance increases from fully discharged to fully pre-charged. The maximum switching frequency, f_{SW_MAX_FET}, occurs when the voltage on the link capacitance reaches its midpoint value, V_BAT/2. This occurs at half the total pre-charge time.

The minimum power transfer of the TPSI31P1-Q1 is limited to 42mW at 85 °C. Since the FET is switching during pre-charge, the total gate charge of the FET must be fully charged and discharged each switching cycle. This minimum power transfer constrains the maximum frequency the TPSI31P1-Q1 can switch the FET. The FET selected has a total gate charge, Q_TOTAL, of 30nC. Assuming V_GS = 15V to ensure full enhancement of the FET, the maximum switching frequency is:

Equation 9.

f_{S W M A X F E T} = \frac{P}{V_{G S} \times Q_{T O T A L}} = \frac{42 m W}{15 V \times 30 n C} = 93.3 k H z

Based on the maximum switching frequency, the minimum inductance, L_MIN, can be computed:

Equation 10.

L_{M I N} \geq \frac{V_{B A T}}{4 \times F_{S W M A X F E T} \times Δ I}

Equation 11.

L_{M I N} \geq \frac{800 V}{4 \times 93.3 k H z \times (4.1 A - 0.53 A)} \geq 600.5 μ H

For this design, two inductors connected in series with a total value of 940μH was selected which reduces the maximum switching frequency to 61.3kHz, well within the power transfer capabilities of the TPSI31P1-Q1. It is important that an inductor be chosen that can support the average and peak currents required. Higher inductor and ΔI values reduce the switching frequency and power requirements.