SLUAAV9 March 2024 LM2005 , LM2101 , LM2103 , LM2104 , LM2105 , LM25101 , LM27222 , LM2724A , LM5100A , LM5100B , LM5100C , LM5101 , LM5101A , LM5101B , LM5101C , LM5102 , LM5104 , LM5105 , LM5106 , LM5107 , LM5108 , LM5109 , LM5109A , LM5109B , LM5109B-Q1 , LM5113-Q1 , LM76003 , LMG1205 , LMG1210 , SM72295 , SM74104 , TPS28225 , TPS28225-Q1 , TPS28226 , TPS2832 , TPS2836 , TPS2837 , UC2950 , UCC27200 , UCC27200-Q1 , UCC27200A , UCC27201 , UCC27201A , UCC27201A-DIE , UCC27201A-Q1 , UCC27211 , UCC27211A , UCC27211A-Q1 , UCC27212 , UCC27212A-Q1 , UCC27222 , UCC27282 , UCC27282-Q1 , UCC27284 , UCC27284-Q1 , UCC27288 , UCC27289 , UCC27301A , UCC27301A-Q1 , UCC27311A , UCC27311A-Q1 , UCC27710 , UCC27712 , UCC27712-Q1 , UCC27714
In common half-bridge gate driver, bootstrap circuit is frequently used to drive two FETs with one power supply. But half-bridge gate driver with bootstrap circuit configuration is unable to drive high side FET with 100% duty cycle. Because the low side FET must be on for a certain time to let power supply charges the bootstrap capacitor up through bootstrap diode. If not, bootstrap capacitor can be unable to provide power for driving high side FET.
For one design to achieve 100% duty-cycle using half-bridge gate driver is to add extra power supply between HB and HS pin of gate driver. Figure 2-1 shows specific schematic. Then the energy to drive high side FET can be provided by this extra power supply instead of bootstrap capacitor. Then the high side FET is able to operate with 100% duty cycle.
The potential risk mainly appears from two reasons:
These two reasons can be analyzed in the following details.