L6924U datasheet(30/38 Pages) STMICROELECTRONICS

30 / 38 page

Additional applications information

L6924U

30/38

Additional applications information

9.1

Selecting input capacitor

In most applications, a 1 µF ceramic capacitor, placed close to the VIN and VINSN pins can

be used to filter the high frequency noise.

9.1.1

Selecting output capacitor

Typically, a 4.7 µF ceramic capacitor placed close to the VOUT and VOUTSN pin is enough to

keep voltage control loop stable. This ensures proper operation of battery absent detection

in removable battery pack applications.

9.2

Layout guidelines and demonstration board

The thermal loop keeps the device at a constant temperature of approximately 120 °C which

in turn, reduces ICHG. However, in order to maximize the current capability, it is important to

ensure a good thermal path. Therefore, the exposed pad must be properly soldered to the

board and connected to the other layer through thermal vias. The recommended copper

thickness of the layers is 70

µm or more.

The exposed pad must be electrically connected to GND. Figure 22 shows the thermal

image of the board with the power dissipation of 1 W. In this instance, the temperature of the

case is 89 °C, but the junction temperature of the device is given by the following formula:

Equation 25

Where the RthJA of the device mounted on board is 75 °C/W, the power dissipated is 1 W,

and the ambient temperature is 25 °C.

In this case the junction temperature is:

Equation 26

AMB

DISS

THJ

−

100

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