SLUSES3 Data sheet

SLUSES3B October 2023 – July 2024 UCC25660

PRODUCTION DATA

8.2.2.16 BLK Pin Voltage Divider

BLK pin senses the LLC DC input voltage and determines when to turn on and off the LLC converter. Also, BLK pin voltage is used for feedforward compensation.

The desired power consumption of the BLK pin resistor divider is P_BLKsns = 15mW. The BLK sense resistor total value is given by:

Equation 50.

R_{B L K s n s} = R_{B L K u p p e r} + R_{B L K l o w e r} = \frac{V_{I N (n o m)}^{2}}{P_{B L K s n s}} = \frac{390^{2}}{0.015} = 10 M Ω

Choose LLC startup voltage as 365V. Then V_BLKStart related to V_BLKStop, V_BLKStartHys, I_BLKSink as below:

Equation 51.

V_{B L K S t a r t} = 365 (\frac{R_{B L K l o w e r}}{R_{B L K u p p e r} + R_{B L K l o w e r}}) = V_{B L K S t o p} + V_{B L K S t a r t H y s} + I_{B L K s i n k} (\frac{R_{B L K u p p e r} R_{B L K l o w e r}}{R_{B L K u p p e r} + R_{B L K l o w e r}})

For V_BLKStop= 1V, V_BLKStartHys= 0.1V, I_BLKSink= $5 μ A$ , $R_{B L K u p p e r}$ and $R_{B L K l o w e r}$ are obtained as $10 M Ω$ and $35.4 k Ω$ respectively.

A standard value of 35.4kΩ is selected for R_BLKlower and a standard value of 3x 3.3MΩ in series is selected for R_BLKupper.

The actual startup voltage is given by

Equation 52.

V_{B L K S t a r t} (\frac{R_{B L K u p p e r} + R_{B L K l o w e r}}{R_{B L K l o w e r}}) = (\begin{array}{l} V_{B L K S t o p} + V_{B L K S t a r t H y s} + \\ I_{B L K Sin k} (\frac{R_{B L K u p p e r} R_{B L K l o w e r}}{R_{B L K u p p e r} + R_{B L K l o w e r}}) \end{array}) \cdot (\frac{R_{B L K u p p e r} + R_{B L K l o w e r}}{R_{B L K l o w e r}}) = 358 V

The power consumption in BLK resistors are given by

Equation 53.

P_{B L K s n s} = \frac{V_{I N (n o m)}^{2}}{(R_{B L K u p p e r} + R_{B L K l o w e r})} = \frac{390^{2}}{(10 M Ω + 35.4 k Ω)} = 15.3 m W

The LLC turn off voltage is given by

Equation 54.

V_{B L K S t o p} (\frac{R_{B L K u p p e r} + R_{B L K l o w e r}}{R_{B L K l o w e r}}) = 280.6 V