L6235Q datasheet(9/33 Pages) STMICROELECTRONICS

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L6235Q

Circuit description

Doc ID 018997 Rev 2

9/33

Circuit description

4.1

Power stages and charge pump

The L6235Q integrates a 3-phase bridge, which consists of 6 power MOSFETs connected

as shown in Figure 1, each power MOSFET has an RDS(ON) = 0.3 Ω (typical value @ 25 °C)

with intrinsic fast freewheeling diode. Switching patterns are generated by the PWM current

controller and the Hall effect sensor decoding logic (Chapter 4.3 on page 11). Cross

conduction protection is implemented by using a dead time (tDT = 1 µs typical value) set by

internal timing circuit between the turn-off and turn-on of two power MOSFETs in one leg of

a bridge.

Pins VSA and VSB must be connected together to the supply voltage (VS).

Using an N-channel power MOSFET for the upper transistors in the bridge requires a gate

drive voltage above the power supply voltage. The bootstrapped supply (VBOOT) is obtained

through an internal oscillator and a few external components to realize a charge pump

circuit, as shown in Figure 5. The oscillator output (pin VCP) is a square wave at 600 kHz

(typically) with 10 V amplitude. Recommended values/part numbers for the charge pump

circuit are shown in Table 5.

Figure 5.

Charge pump circuit

Table 5.

Charge pump external component values

Component

Value

CBOOT

220 nF

10 nF

100

1N4148

AM02559v1

CBOOT

VSA

VCP

VBOOT

VSB

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