ZHCSJQ0A may 2019 – july 2023 LM5108
PRODUCTION DATA
- 1
- 1 特性
- 2 应用
- 3 说明
- 4 Revision History
- 5 Pin Configuration and Functions
- 6 Specifications
- 7 Detailed Description
- 8 Application and Implementation
- 9 Power Supply Recommendations
- 10Layout
- 11Device and Documentation Support
- 12Mechanical, Packaging, and Orderable Information
8.2.2.3 Selecting External Gate Resistor
In high-frequency switching power supply applications where high-current gate drivers such as the LM5108 are used, parasitic inductances, parasitic capacitances and high-current loops can cause noise and ringing on the gate of power MOSFETs. Often external gate resistors are used to damp this ringing and noise. In some applications the gate charge, which is load on gate driver device, is significantly larger than gate driver peak output current capability. In such applications external gate resistors can limit the peak output current of the gate driver. it is recommended that there should be provision of external gate resistor whenever the layout or application permits.
Use Equation 9 to calculate the driver high-side pull-up current.
where
- IOHH is the high-side, peak pull-up current
- VDH is the bootstrap diode forward voltage drop
- RHOH is the gate driver internal high-side pull-up resistor. Value either directly provided in datasheet or can be calculated from test conditions (RHOH = VHOH/IHO)
- RGATE is the external gate resistance connected between driver output and power MOSFET gate
- RGFET(int) is the MOSFET internal gate resistance provided by MOSFET datasheet
Use Equation 10 to calculate the driver high-side sink current.
where
- RHOL is the gate driver internal high-side pull-down resistance
Use Equation 11 to calculate the driver low-side source current.
where
- RLOH is the gate driver internal low-side pull-up resistance
Use Equation 12 to calculate the driver low-side sink current.
where
- RLOL is the gate driver internal low-side pull-down resistance
Typical peak pull up and pull down current of the device is 1.6 A and 2.6 A respectively. These equations help reduce the peak current if needed. To establish different rise time value compared to fall time value, external gate resistor can be anti-paralleled with diode-resistor combination as shown in Figure 8-1. Generally selecting an optimal value or configuration of external gate resistor is an iterative process. For additional information on selecting external gate resistor please refer to External Gate Resistor Design Guide for Gate Drivers