RT9603 Ver la hoja de datos (PDF) - Richtek Technology
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Fabricante
RT9603 Datasheet PDF : 10 Pages
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RT9603
VCC
1N4148
VIN
BST
DRVH
SW
CB
+
VCB
-
Figure 5 shows the power dissipation of the RT9603 as a
function of frequency and load capacitance. The value of
the CU and CL are the same and the frequency is varied
from 100kHz to 1MHz.
Power Dissipation vs. Frequency
1000
VCC
DRVL
PGND
900
CU=CL=3nF
800
700
600
500
Figure 3. Part of Bootstrap Circuit of RT9603
400
CU=CL=2nF
In practice, a low value capacitor CB will lead the over-
charging that could damage the IC. Therefore to minimize
the risk of overcharging and reducing the ripple on VCB,
the bootstrap capacitor should not be smaller than 0.1μF,
and the larger the better. In general design, using 1μF
can provide better performance. At least one low-ESR
capacitor should be used to provide good local de-
coupling. Here, to adopt either a ceramic or tantalum
capacitor is suitable.
300
CU=CL=1nF
200
100
0
0
200
400
600
800
1000
Frequency (kHz)
Figure 5. Power Dissipation vs. Frequency
The operating junction temperature can be calculated
from the power dissipation curves (Figure 5). Assume
VCC=12V, operating frequency is 200kHz and the
Power Dissipation
For not exceeding the maximum allowable power
dissipation to drive the IC beyond the maximum
recommended operating junction temperature of 125°C,
it is necessary to calculate power dissipation appro-
priately. This dissipation is a function of switching
frequency and total gate charge of the selected MOSFET.
Figure 4 shows the power dissipation test circuit. CL and
CU are the DRVH and DRVL load capacitors, respectively.
The bootstrap capacitor value is 0.01μF.
10
+12V
1uF
1N4148
1uF
CBST
BST
VCC
DRVH
RT9603
SW
PWM
IN
DRVL
PGND
+12V
2N7002
CU
3nF
2N7002
20
CL
3nF
CU=CL=1nF which emulate the input capacitances of the
high side and low side power MOSFETs. From Figure 5,
the power dissipation is 100mW. For RT9603, the package
thermal resistance θJA is 160°C/W, the operating junction
temperature is calculated as :
TJ = (160°C/W x 100mW) + 25°C = 41°C (11)
where the ambient temperature is 25°C.
The method to improve the thermal transfer is to increase
the PCB copper area around the RT9603 first. Then, adding
a ground pad under IC to transfer the heat to the peripheral
of the board.
Figure 4. Test Circuit
www.richtek.com
8
DS9603-08 March 2007
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