AN4823 Application note L99DZ80EP/L99DZ81EP H-bridge driver switching consideration and Rgate calculation Introduction This document gives information about H-bridge driver embedded in the L99DZ80EP and L99DZ81EP: those devices include an SPI-programmable slew-rate circuit that drives 4 external MOSFETs in a H-bridge configuration supporting electric-window applications. February 2016 DocID028918 Rev 2 1/8 www.st.com Block diagram 1 AN4823 Block diagram Figure 1: L99DZ80EP and L99DFZ81EP block diagram L99DZ80EP and L99DZ81EP devices provide, through pins GH1/2, GL1/2 and SL1/2, dedicated driving signals to the external 4 MOSFETs. 2/8 DocID028918 Rev 2 AN4823 2 L99DZ80EP/L99DZ81EP smart switching details L99DZ80EP/L99DZ81EP smart switching details Figure 2: Simplified schematic of driver for external high-side Chargepump Voltage VS VCP ~(VS + 10V) Icharge SWIC RSW = 6Ω SWRCSW Measure VDS C1 VDSSW TH VGSSW VGate RGate V GS VDS SWCVSW Measure VGS CVSW SWID C2 SWRDSW Idischarge RSW = 6Ω Motor Inductor VSource TL R SW = 6Ω, typical design value GAPG2601160917CFT Typical curves are described in the following figure. DocID028918 Rev 2 3/8 L99DZ80EP/L99DZ81EP smart switching details AN4823 Figure 3: H-bridge GSHx slope Some transitions are now analyzed: Transition A Threshold voltage ext FET sampled and stored in CVSW during Miller Plateau ↔ VTH. During this phase, threshold stored in CVSW during Miller Plateau is increased by ICharge * RGate in reference to VTH of the external MOSFET Transition B Switch-off started with RSW , "hard switching". Transition C • • • Reaching VTH, RSW is turned-off by opening SW RDSW Opening of SW RDSW is done with a certain delay Afterwards gate discharge is done by the programmed current source (Idischarge) During this phase, VGate is decreased by resistive divider RSW ↔ Rgate and "Virtually" the threshold to switch from switch mode to current mode is lower than real gate source voltage on external FET. Figure 4: "Transition C measurement on a real device" shows measurements performed on a real device. 4/8 DocID028918 Rev 2 AN4823 L99DZ80EP/L99DZ81EP smart switching details Figure 4: Transition C measurement on a real device 2.1 How to choose a proper Rgate resistance Charge in the beginning of turn-off phase is discharged by the hard switch in series with the external gate resistance. Average current during this phase is approximately (5V + VTH/2) / (RSW + RGate). Due to virtual decreased sample voltage (by resitive divider RSW & RGate) the transistion from switch mode to current control mode is started almost immediately after start of turnoff of ext FET (depending on size of RGate). Delay of opening SW RDSW is approximately 100 ns (typical value). During this time Qgate must NOT be discharged to ensure to enter QGD plateau. As rule of thumb the according Rgate can be calculated by the following formula: RGate ≥ (5V + VTH/2) * 100ns / QGate - RSW That value of RGate is needed to enter current source mode. DocID028918 Rev 2 5/8 L99DZ80EP/L99DZ81EP smart switching details AN4823 Table 1: Rgate values as per different MOSFET choice QTotal (nC) QGD (nC) QGS (nC) QTotal – QGD – QGS (nC) VTH @ 40A (V) Calculated RGate ≈ (Ω) ST STD64N4F6AG 44 15 12 18 5.5 38 ST STD80N4F6AG 36 9 11 16 4.8 41 ST VNH7013 36 5 8,5 22.5 Not specified (2 ... 4) 28 (@VTH = 5V) Supplier A 45 12.6 10 22.4 4V 26 Supplier B 17.2 2.4 8 6.8 5.5V 109 MOSFET 6/8 DocID028918 Rev 2 AN4823 3 Revision history Revision history Table 2: Document revision history Date Revision 17-Feb-2016 1 Initial release. 2 Updated Figure 2: "Simplified schematic of driver for external high-side" Section 2.1: "How to choose a proper Rgate resistance": 29-Feb-2016 Changes • Updated equation DocID028918 Rev 2 7/8 AN4823 IMPORTANT NOTICE – PLEASE READ CAREFULLY STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, enhancements, modifications, and improvements to ST products and/or to this document at any time without notice. Purchasers should obtain the latest relevant information on ST products before placing orders. ST products are sold pursuant to ST’s terms and conditions of sale in place at the time of order acknowledgement. Purchasers are solely responsible for the choice, selection, and use of ST products and ST assumes no liability for application assistance or the design of Purchasers’ products. No license, express or implied, to any intellectual property right is granted by ST herein. Resale of ST products with provisions different from the information set forth herein shall void any warranty granted by ST for such product. ST and the ST logo are trademarks of ST. All other product or service names are the property of their respective owners. Information in this document supersedes and replaces information previously supplied in any prior versions of this document. © 2016 STMicroelectronics – All rights reserved 8/8 DocID028918 Rev 2