External components

AN4370

20/23

DocID025336 Rev 1

11

External components

Since the source and sink currents of the L99ASC03 gate drivers are adjustable via SPI,

there is no need to have gate resistors to control the MOSFETs slew rate. However, gate

resistors may be used to dampen the ringing that could slow down the MOSFET turn-on.

External resistors between gate and source of each MOSFET could be used as an

additional safety measure against accidental disconnection of the MOSFET gate pins from

the driver. In fact, an internal resistor is present between each gate pin and the related

source pin of the device to prevent the gate from floating.

There is no need for an external VGS clamp either, since there is an internal circuit that will

keep the VGS between the following values: VSLx + 9 / VSHx + 9 and

VSLx + 13 / VSHx + 13. The capacitor between VSMS and GND has to be sized according

to the application. Due to the Drain Source Monitoring we recommend connecting each SLx

and SHx pin directly to the source of the corresponding MOSFET, in order to have separate

paths. The direct drive inputs have internal pull-ups and pull-downs in order to avoid an

accidental turn-on of the MOSFETs due to noise. Be careful that the BC input pin absolute

max rating is 20 V. VDD must have at least 660 nF (ESR < 50 m

Ω) connected between

VDD and GND, close to VDD, with a minimum load of 6 mA. The capacitance between

CPx+ and CPx- should be 220nF, while the capacitance between CP and VS should be

1 µF. As shown in Figure 11, it is recommended to insert a 100 k

Ω resistor between the CP

pin and the gate of the reverse battery protection MOSFET to minimize the current flowing

in case of reverse battery.

VS and VSREG should have a 100 nF ceramic capacitor placed close to each pin and GND

and also an electrolytic capacitor to be sized depending on application. We recommend

placing a 10K series resistor followed by a 100 nF cap at the INH pin to protect it against

ESD up to ±6 KV coming from the module connector.