Points to note when developing Renesas high-voltage MOS products

This article mainly introduces the selection and characteristics of Renesas Electronics (also known as: Renesas Note 1) high-voltage MOS in the development of customer power supplies and other products, and provides reference design opinions for customer product development.

MOSFET is widely used in power supplies and other products due to its advantages such as voltage control, high switching frequency, and fast switching speed. Renesas high-voltage MOS covers drain-source voltage (VDSS) levels of 600V, 800V, 900V, and 1400V, with extremely low RDS(ON) and a rich package series, and is widely used.

The two most important parameters of MOSFET are drain-source voltage (VDSS) and on-resistance RDS(ON). The current value and maximum power dissipation value must be carefully observed because they can only be achieved when the backplane temperature reaches 25OC, and the switching time is only applicable when the specific conditions described in the data sheet are met.

Generally speaking, the Renesas high-voltage MOS data sheet mainly contains the following parts: characteristics, limit values, electrical characteristics, and typical characteristics.

The performance advantages of Renesas high-voltage MOS:

relatively low Qg

Vgs voltage ±30 V

relatively low on-resistance

Good anti-avalanche capability

Renesas MOS uses the fifth generation UMOS process, which can make RDS(ON) relatively small. The on-resistance of 2SK3298B is only 0.75 ohms, which can greatly reduce the loss of MOS.

The limit value section gives the absolute maximum values ​​of 10 parameters. The device must not exceed this value when it is running, otherwise it will cause permanent damage to the MOS. Among them, it is particularly important to note that the values ​​of drain current and dissipated power are given at 25OC, which can only be used as a reference in actual operation.

The electrical characteristics section mainly contains several important parameters: turn-on and turn-off time parameters, transconductance parameters, junction capacitance parameters, and internal diode parameters. Renesas high-voltage MOS generally switches faster than other brands of MOS of the same type, but there is a very important prerequisite: the gate drive voltage must be above 10V, because the junction capacitance parameters of Renesas high-voltage MOS are relatively large.

The typical characteristics section gives dynamic curves of many parameters. The more important parameter curves are: thermal resistance curve, transfer characteristic curve, transconductance curve, on-resistance and drain current relationship curve, and dissipated power and temperature relationship curve. The dissipated power decreases with the increase of temperature, and the on-resistance increases with the increase of temperature.

Renesas high-voltage MOS has the obvious advantages of low on-resistance and fast switching speed, but the quality of the driving circuit directly affects the characteristics of MOS. In order to achieve good driving waveform and switching characteristics, so that the tube can work in a more ideal state, it is now analyzed in combination with several parameter effects and typical curves Note 2 in the data sheet.

1. RDS (ON) change curve with VGS:


As can be seen from the figure, when VGS is less than 10V, RDS(ON) is relatively large, especially when it is less than 7-8V, RDS(ON) is almost infinite, and the tube is almost not turned on. Therefore, we recommend that the driving voltage should generally be above 10V, so that a relatively low on-resistance can be obtained and the loss of MOS can be reduced.

2. From the data sheet, it is known that the CISS, COSS, and CRSS of Renesas high-voltage MOS are relatively large, so in order to obtain a better driving waveform, it is recommended that the gate drive resistance should not be too large, and try to be in tens of ohms.

3. Transconductance parameters and curves. Transconductance is a very important parameter of MOS, which reflects the control ability of the gate drive voltage on the drain current. From the transfer characteristic curve in the figure below, it can be seen that when the MOS gate drive voltage is around 10V, the MOS drain current can reach the nominal value.


The above analysis has analyzed some characteristics of Renesas high-voltage MOS and some parameter coordination to achieve better switching characteristics. Now to summarize the above points, Renesas authorized agent Shiqiang Telecom gives the following suggestions for your reference in product development:

The gate drive voltage should be above 10V, which can obtain a better drive waveform and lower on-resistance, and can reduce the heat and loss of MOS.

The gate drive resistor is best to make a suitable choice between EMI and drive waveform, preferably tens of ohms. The drive resistor is 25 ohms in the test conditions of the parameters in the Renesas data sheet.

Because the gate-source withstand voltage of Renesas high-voltage MOS is relatively high, it can reach 30V. Therefore, in the case of heavy load or large drain current, in order to avoid the drain current out of control MOS entering the amplification area, the gate drive voltage should be appropriately increased, as long as it does not exceed the nominal 30V.