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AN2839 Datasheet(PDF) 11 Page - STMicroelectronics |
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AN2839 Datasheet(HTML) 11 Page - STMicroelectronics |
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11 / 40 page  AN2839 Designing an application with L6228 Doc ID 15104 Rev 1 11/40 To minimize interferences with the rest of the circuit, care must be taken in realizing the PCB layout of the C5, D1 and D2 connections (also see Section 1.4). The recommended values for the charge pump circuitry are: ● D1, D2: 1N4148 ● C5: 10 nF, 100 V ceramic ● C8: 20 nF, 25 V ceramic Due to the high charge-pump frequency, fast diodes are required. When connecting the cold side of the bulk capacitor (C8) to VS instead of GND, the average current in the external diodes during operation is less than 10 mA; at startup (when VS is provided to the IC) it is less than 200 mA while the reverse voltage is about 10 V in all conditions. IN4148 diodes withstand about 200 mA of DC current (1 A peak), and the maximum reverse voltage is 75 V, so they should fit for the majority of applications. 1.7 Sharing the charge pump circuitry If more than one device is used in the application, the charge pump from one L6228 can be used to supply the VBOOT pins of several ICs. The unused CP pins on the slaved devices are left unconnected, as shown in Figure 8. A 100 nF capacitor (C8) should be connected to the VBOOT pin of each device. The supply voltage pins VS of the devices sharing the charge pump must be connected together. The higher the number of devices sharing the same charge pump, the lower the differential voltage available for the gate drive (VBOOT - VS), causing a higher RDS(on) for the high-side DMOS, and as such a higher dissipating power. Better performance can also be obtained using a 33 nF capacitor for C5 and Schottky diodes (BAT47 are recommended). Having more than three or four devices sharing the same charge-pump circuitry is not recommended since this will reduce the VBOOT voltage and increase the high-side MOSFET’s on-resistance, and therefore the power dissipation. Figure 8. Sharing the charge-pump circuitry |
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