RT7207 datasheet(24/25 Pages) RICHTEK

24 / 25 page

RT7207

DS7207-00 January 2017

www.richtek.com

is a registered trademark of Richtek Technology Corporation.

Figure 12. OVP Pin Block Diagram

Figure 13. Timing Sequence of the OVP Pin Function

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. The maximum power

dissipation at TA = 25

°C can be calculated as below :

PD(MAX) = (125

°C − 25°C) / (28°C/W) = 3.57W for a

WQFN-24L 4x4 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 14 allows

the designer to see the effect of rising ambient temperature

on the maximum power dissipation.

Figure 14. Derating Curve of Maximum Power Dissipation

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

100

125

Ambient Temperature (°C)

Four-Layer PCB

VREF_CV

OPTO

BLD_EN

x1.2/x1.25/x1.3

VFB

RFB1

RFB2

VDD

RD2

VVDD_OFF

ADC

MCU

INT_

“VDDOV”

VOUT

OVP

VOUT

INT_VDDOV

VOVP

OV hys

tD_VOUTOVP

VDD = VVDD_OFF

Debounce time of latched OPTO by MCU is around 10µs

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