AN4243 datasheet(11/29 Pages) STMICROELECTRONICS

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AN4243

Designing an application with the L6230

Doc ID 024199 Rev 1

11/29

Figure 7.

Charge pump circuitry

When the oscillator output is at ground, Cfly is charged by Vs through D2. When it rises to 10

V, D2 is reverse biased and the charge flows from Cfly to Cboot through D1, so the VBOOT

pin, after some few cycles, reaches the maximum voltage of Vs + 10 V VD1 VD2, which

supplies the high-side gate drivers.

With a differential voltage between VS and VBOOT of about 9 V and both the bridges

switching at 50 kHz, the typical current drawn by the VBOOT pin is 1.85 mA.

Care must be taken to develop the PCB layout of Cfly, D1, D2 connections in order to

minimize interferences with the rest of the circuit (see also the Section 2.4).

Recommended values for the charge pump circuitry are:

●

D1, D2 : 1N4148

●

Cfly

: 10 nF - 100V (ceramic capacitor)

●

Cboot

: 220 nF - 35V (ceramic capacitor)

Due to the high charge pump frequency, fast diodes are required. Connecting the cold side

of the bulk capacitor (C2) to VS instead of GND, the average current in the external diodes

during operation is less than 10 mA. At IC power-up the current in the external diodes during

operation is less than 200 mA. The reverse voltage is about 10 V in all conditions. The

1N4148 diodes withstand about 200 mA DC (1 A peak), and the maximum reverse voltage

is 75 V, so they should fit for the majority of applications.

L6230

VS-VD1

f = 600 kH

VSA

VSB

VBOOT

Cboot

Cﬂy

10 V

To High-Side

10 V

f = 600 kH

Charge Pump

Oscillator

VS+ 10 V- VD1 - VD2

VS+ 10 V- VD1

AM16569v1

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