AN4370 datasheet(18/23 Pages) STMICROELECTRONICS

Part #	AN4370

Description	L99ASC03 PMBLDC sensorless 3-phase motor driver

PDF	23 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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18 / 23 page

Calculation example

AN4370

18/23

DocID025336 Rev 1

Calculation example

Let’s assume the following use conditions:

VVSREG =VVS =12V

IVDD =20mA

QG = 60nC

fPWM =25kHz

N= 6

From the above mentioned formulas for PVDD and PREG, we get

PVDD =(VVSREG - VVDD) x IVDD = (12V - 5V) x 20mA = 140mW

PREG =VVSREG x IVSREG = 12V x 25mA = 300mW

The load at the charge pump output due to the external MOSFETs is

ICP =N x fPWM x QG =9mA

By looking at Figure 10, for a charge pump load of 10mA (

≈ 9mA) at V

VS = 12V, the input

current IVS is 44mA. The power consumption from the VS pin can be estimated as

PVS =VVS x IVS = 12V x 44mA = 528mW

The worst-case total power dissipation PD can thus be estimated as

PD =PVDD + PREG + PVS = 140mW + 300mW + 528mW = 968mW

AN4370 Datasheet(PDF) 18 Page - STMicroelectronics