RT8207LZQW datasheet(24/27 Pages) RICHTEK

24 / 27 page

DS8207L/M-08 September 2016

www.richtek.com

RT8207L/M

is a registered trademark of Richtek Technology Corporation.

Figure 9. Derating Curve of Maximum Power Dissipation

Layout Considerations

Layout is very important in high frequency switching

converter design. If designed improperly, the PCB could

radiate excessive noise and contribute to the converter

instability. Certain points must be considered before

starting a layout for the RT8207L/M.



Connect an RC low pass filter from VDDP to VDD; 1

μF

and 5.1

Ω are recommended. Place the filter capacitor

close to the IC.



Keep current limit setting network as close as possible

to the IC. Routing of the network should avoid coupling

to high voltage switching node.



Connections from the drivers to the respective gate of

the high side or the low side MOSFET should be as

short as possible to reduce stray inductance.



All sensitive analog traces and components such as

VDDQ, FB, PGND, PGOOD, CS, VDD, and TON should

be placed away from high voltage switching nodes such

as PHASE, LGATE, UGATE, and BOOT to avoid

coupling. Use internal layer(s) as ground plane(s) and

shield the feedback trace from power traces and

components.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

100

125

Ambient Temperature (°C)

Four-Layer PCB

WQFN-24L 4x4

WQFN-20L 3x3

Thermal Considerations

The junction temperature should never exceed the

absolute maximum junction temperature TJ(MAX), listed

under Absolute Maximum Ratings, to avoid permanent

damage to the device. The maximum allowable power

dissipation depends on the thermal resistance of the IC

package, the PCB layout, the rate of surrounding airflow,

and the difference between the junction and ambient

temperatures. The maximum power dissipation can be

calculated using the following formula :

PD(MAX) = (TJ(MAX)

− TA) / θJA

where TJ(MAX) is the maximum junction temperature, TAis

the ambient temperature, and

θJA is the junction-to-ambient

thermal resistance.

For continuous operation, the maximum operating junction

temperature indicated under Recommended Operating

Conditions is 125

°C. The junction-to-ambient thermal

resistance,

θJA, is highly package dependent. For a

WQFN-24L 4x4 package, the thermal resistance,

θJA, is

°C/W on a standard JEDEC 51-7 high effective-thermal-

conductivity four-layer test board. For a WQFN-20L 3x3

package, the thermal resistance,

θJA, is 68°C/W on a

standard JEDEC 51-7 high effective-thermal-conductivity

four-layer test board. The maximum power dissipation at

TA = 25

°C can be calculated as below :

PD(MAX) = (125

°C − 25°C) / (52°C/W) = 1.923W for a

WQFN-24L 4x4 package.

PD(MAX) = (125

°C − 25°C) / (68°C/W) = 1.471W for a

WQFN-20L 3x3 package.

The maximum power dissipation depends on the operating

ambient temperature for the fixed TJ(MAX) and the thermal

resistance,

θJA. The derating curves in Figure 9 allows

the designer to see the effect of rising ambient temperature

on the maximum power dissipation.

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