RT9624F datasheet(11/13 Pages) RICHTEK

11 / 13 page

RT9624F

DS9624F-02

July 2015

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Figure 2. Part of Bootstrap Circuit of RT9624F

In practice, a low value capacitor CBOOT will lead to the

over charging that could damage the IC. Therefore, to

minimize the risk of overcharging and to reduce the ripple

on VCB, the bootstrap capacitor should not be smaller than

0.1

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

μF can provide better performance.At least one low-ESR

capacitor should be used to provide good local de-coupling.

It is recommended to adopt a ceramic or tantalum

capacitor.

Power Dissipation

To prevent driving the IC beyond the maximum

recommended operating junction temperature of 125

°C,

it is necessary to calculate the power dissipation

appropriately. This dissipation is a function of switching

frequency and total gate charge of the selected MOSFET.

Figure 3 shows the power dissipation test circuit. CL and

CU are the UGATE and LGATE load capacitors,

respectively. The bootstrap capacitor value is 1

μF.

Figure 3. Power Dissipation Test Circuit

Figure 4 shows the power dissipation of the RT9624F as

a function of frequency and load capacitance when VCC =

12V. The value of CUand CL are the same and the frequency

is varied from 100kHz to 1MHz.

The operating junction temperature can be calculated from

the power dissipation curves (Figure 4). Assume

VCC = 12V, operating frequency is 200kHz and CU = CL =

1nF which emulate the input capacitances of the high-

side and low-side power MOSFETs. From Figure 4, the

power dissipation is 100mW. Thus, for example, the

package thermal resistance

θJA is 120°C/W. The operating

junction temperature is then calculated as :

TJ = (120

°C/W x 100mW) + 25°C = 37°C

(11)

where the ambient temperature is 25

°C.

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 :

PD(MAX) = (TJ(MAX)

− TA) / θJA

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

the ambient temperature, and

θJAis the junction to ambient

thermal resistance.

Figure 4. Power Dissipation vs. Frequency

VIN

CBOOT

VCB

BOOT

VCC

UGATE

PHASE

LGATE

GND

Power Dissipation vs. Frequency

100

200

300

400

500

600

700

800

900

1000

200

400

600

800

1000

Frequency (kHz)

VCC = 12V

CU = CL = 1nF

CU = CL = 3nF

CU = CL = 2nF

VCC

PWN

GND

BOOT

UGATE

PHASE

LGATE

RT9624F

1µF

3nF

2N7002

12V

1µF

PWM

CBOOT

3nF

RT9624F Datasheet(PDF) 11 Page - Richtek Technology Corporation

RT9624F Datasheet(HTML) 11 Page - Richtek Technology Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13

Datasheet Download

Link URL