SLUAAP4 October   2023 LM2005 , LM2101 , LM2103 , LM2104 , LM2105 , LM5108 , UCC27301A , UCC27311A , UCC27531 , UCC27710 , UCC44273

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Gate Driver IC Configurations
  6. 3Key Voltage and Current Specifications
    1. 3.1 Voltage Ratings
    2. 3.2 Peak Current
  7. 4Robustness Features
    1. 4.1 Undervoltage Lockout
    2. 4.2 Negative Voltage Handling
    3. 4.3 Cross-Conduction Protection
  8. 5Board Space, Thermal Performance, and Other Considerations
  9. 6Summary
  10. 7References

3.2 Peak Current

Typically, DC motor drive systems operate at lower frequencies (compared to power conversion applications) and thus do not require high current specifications. Thus, drivers optimized for motor applications often have peak currents less than 2 A. To drive multiple power switches in parallel or operate at higher frequencies, look to devices with fast switching characteristics and peak currents around 3 A or higher. For these reasons, higher-current devices can also be a good choice for driving the coil arrays of a linear motor power stage.

The minimum drive strength required by a system depends on characteristics of the system and gate driver. To estimate the minimum drive strength required, one must consider the parameters shown in Table 3-1.

Table 3-1 Summary of Parameters Used to Calculate Minimum Drive Strength for a Gate Driver
ParameterInformation source Example valueRelationship

VGS

Desired gate-source voltage

System parameter12 VHigher values typically require higher current.

QG,max

Maximum gate charge at desired VGS

Power switch data sheet (VGS vs. QG curve, or maximum value in electrical characteristics table)15 nCHigher values typically require higher current.

TON,OFF

Desired rise and fall time

System parameter(1)60 nsLower values (faster switching) typically require higher current.

N

Number of power switches driven by one driver output

System1 switchHigher values (more switches in parallel) typically require higher current.

With this information, one can estimate the equivalent capacitance (Ceq):

Equation 1. Ceq=QG,max×NVGS=15 nC ×1 switch12 V=54 nF

Which in turn, provide the minimum peak current:

Equation 2. IPK,min=Ceq× dVdt=54 nF×12 V60 ns=0.25 A

This example suggests choosing a driver with peak current specifications of at least 0.25 A. So, the peak drive strength capability of a driver like LM2105 (0.5 A/0.8 A) can suffice. To easily estimate this, please see the Excel tool provided in [FAQ] LM2105: Half-Bridge Gate Driver Minimum Current Calculator. For further explanation of key gate driver parameters mentioned previously, see Fundamentals of MOSFET and IGBT Gate Driver Circuits.

1. This parameter refers to the rise and fall time of the power switch’s input (for example, the gate of the MOSFET). This is also closely related to the rise and fall time of the switch node.