RT9603CS datasheet(8/10 Pages) RICHTEK

8 / 10 page

RT9603

Preliminary

DS9603-00

November 2003

www.richtek.com

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Frequency (kHz)

CU=CL=3nF

CU=CL=1nF

CU=CL=2nF

Power Dissipation vs. Frequency

Figure 3. Part of Bootstrap Circuit of RT9603

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 0.1

µF,

and the larger the better. In general design, using 1

µF

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.

Power Dissipation

For not exceeding the maximum allowable power

dissipation to driv e 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 0.01

µF.

Figure 4. Test Circuit

Figure 5 shows the power dissipation of the RT9603 as

a function of frequency and load capacitance. The value

of the CU and CLare the same and the frequency is varied

from 100kHz to 1MHz.

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

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 67° C/W, the operating

junction temperature is calculated as:

TJ = (67°C/W x 100mW) + 25°C = 31.7°C

(11)

where the ambient temperature is 25

°C.

The method to improve the thermal transfer is to increase

the PC board copper area around the RT9603 firstly.

Then, adding a ground pad under IC to transfer the heat

to the peripheral of the board.

VIN

VCB

BST

VCC

DRVH

DRVL

PGND

1N4148

VCC

PGND

BST

DRVH

DRVL

RT9603

1uF

3nF

2N7002

+12V

1uF

PWM

1N4148

CBST

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