AN2836 datasheet(16/57 Pages) STMICROELECTRONICS

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Designing an application with L6225, L6226, L6227

AN2836

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Doc ID 15084 Rev 1

4.6

Charge pump external components

An internal oscillator, with its output at the CP pin, switches from GND to 10 V with a typical

frequency of 600 kHz (see Figure 9).

Figure 9.

Charge pump

When the oscillator output is at ground, C5 is charged by VS through D2. When it rises to

10, D2 is reverse biased and the charge flows from C5 to C8 through D1, so the VBOOT pin,

after a 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 in establishing the PCB layout of the C5, D1, D2 connections in order to

minimize interferences with the rest of the circuit (see also Section 4.4). Recommended

values for the charge pump circuitry are:

●

D1, D2: 1N4148

●

C5: 10 nF 100 V ceramic

●

C8: 220 nF 25 V ceramic

Due to the high charge pump frequency, fast diodes are required. 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 IC power-up the current in the external diodes is

less than 200 mA. The reverse voltage of the charge pump diodes is about 10 V in all

Table 1.

RSENSE recommended values

Ipk

RSENSE value [Ω]RSENSE power rating [W]

Alternatives

0.25

0.125

0.5

0.25

10.5

0.5

2 X 1

Ω, 0.25 W

paralleled

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