RT9553A Datasheet, PDF (11/12 Pages) Richtek Technology Corporation – High Accuracy Current/Voltage Sensing and Protection IC

RT9553A
VCC
EN
3ms
V_CSP x (1/9)
108%_UVSET
UVSET
RESET
Recovery Hysteresis Range
Figure 5. UVP and RESET Indicator Illustrator
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
P_D(MAX) = (T_J(MAX) − T_A) / θ_JA
where T_J(MAX) is the maximum junction temperature, T_A is
the ambient temperature, and θ_JA is the junction to ambient
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θ_JA, is layout dependent. For
WDFN-10L 3x3 package, the thermal resistance, θ_JA, is
30.5°C/W on a standard JEDEC 51-7 four-layer thermal
test board. The maximum power dissipation at T_A = 25°C
can be calculated by the following formula :
P_D(MAX) = (125°C − 25°C) / (30.5°C/W) = 3.27W for
WDFN-10L 3x3 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T_J(MAX) and thermal
resistance, θ_JA. The derating curve in Figure 6 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Copyright ©2014 Richtek Technology Corporation. All rights reserved.
DS9553A-00 September 2014
3.5
Four-Layer PCB
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 6. Derating Curve of Maximum Power Dissipation
Layout Considerations
Layout is very important in RT9553A, if designed
improperly, the PCB may radiate excessive noise. Certain
points must be considered before starting a layout for the
RT9553A.
 Connect a RC low pass filter to VCC. The recommended
BOM of RC filter is 2.2Ω and 0.1μF. Place the filter
capacitor close to the IC.
 Current sense connections must always be made using
Kelvin connections to ensure an accurate signal with
the current limit resistor located at the device.
 All sensitive analog traces and components such as
CSP, CSN, VCC, EN, PROCHOT, RESET and ILIM
should be placed away form high voltage switching
nodes to avoid coupling.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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