What is the maximum gate charge that the TLE9185 can drive?

[Infineon_Team]

Let´s start considering the current capability of the charge pump = 12 mA, (min value of I_CPOC, parameter P_12.11.68/P_12.11.69).

Assumptions:

• 3 half-bridges are controlled in PWM at the same time
• all MOSFETs are symmetrical (same gate charge)
• active freewheeling is enabled
• PWM frequency (FPWM) : 20 kHz

The gate of 3 MOSFETs in PWM and 3 freewheeling MOSFETs must be periodically charged.

The average current delivered by the charge pump is:

I_CPOC= 3 x 2 x Q_GMAX x F_PWM 

Q_GMAX = I_CPOC / 6 F_PWM

Q_GMAX = 12 mA / (6 x 20000) = 100 nC

Where Q_GMAX is the maximum gate charge for one MOSFET.

The factor 3 is for the number of half-bridges operating in PWM at the same time.

The factor 2 is for the PWM MOSFET and the freewheeling MOSFET of each half-bridge in PWM.

Q_GMAX = 100nC is related to V_GS = 11 V typ. for the TLE9185, whereas the Q_G of the MOSFET is in general specified at V_GS = 10V.

Therefore the device can drive MOSFETs with a total gate charge of 90 nC at V_GS = 10 V, when 3 half-bridges are simultaneously driven in PWM 

The other limiting factor is the total power dissipation, which depends on the V_CC1 current, on the ambient temperature and the thermal cooling of the package.

Note: if one half-bridge is activated without PWM, it must not be considered in the average current delivered by the charge pump.