RT9724 RICHTEK [Richtek Technology Corporation], RT9724 Datasheet - Page 10

• Manufacturer Part Number: RT9724
• Description: 100m?, 2A Slew Rate Controlled Load Switch
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9724
The resistance of the switch is defined as follows :
R
If the voltage drop across the PCB is limited to 100mV,
the maximum resistance for the switch is 250mΩ for four
ports ganged together. The RT9724, with its maximum
100mΩ on-resistance over temperature, can fit the demand
of this requirement.
Thermal Shutdown
Thermal protection limits the power dissipation in the
RT9724. When the operation junction temperature
exceeds 130°C, the OTP circuit starts the thermal
shutdown function and turns the pass element off. The
pass element turn on again after the junction temperature
cools to 80°C. The RT9724 lowers its OTP trip level from
130°C to 100°C when output short circuit occurs (V
1V) as shown in Figure 1.
Copyright
www.richtek.com
10
Shutdown
Figure 1. Short Circuit Thermal Folded Back Protection
Thermal
IC Temperature
SWITCH
OTP Trip Point
V
I
OUT
OUT
when Output Short Circuit Occurs (Patent)
©
= (200mV − V
= { 4.75V − 4.4V − [ 0.5A x ( 4
2012 Richtek Technology Corporation. All rights reserved.
90mΩ) ] − V
130 C
V
OUT
°
Short to GND
110 C
°
PCB
80 C
100 C
PCB
°
°
)
}
÷
÷
( 0.1A x N
( 0.1A x N
PORTS
PORTS
x
30mΩ + 2 x
)
)
1V
OUT
<
Thermal Considerations
The maximum power dissipation depends on the thermal
resistance of IC package, PCB layout, the rate of
surroundings airflow and temperature difference between
junction to ambient. The maximum power dissipation can
be calculated by following formula :
P
where T
the ambient temperature, and θ
thermal resistance.
For recommended operating conditions specification, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance θ
SOT-23-5 package, the thermal resistance θ
218.1°C/W on the standard JEDEC 51-7 four layers
thermal test board. For WDFN-8L 2x2 package, the
thermal resistance θ
51-7 four layers thermal test board. The maximum power
dissipation at T
formula :
P
SOT-23-5 package
P
WDFN-8L 2x2 package
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance θ
designer to see the effect of rising ambient temperature
on the maximum power allowed.
Figure 2. Derating Curve of Maximum Power Dissipation
D(MAX)
D(MAX)
D(MAX)
is a registered trademark of Richtek Technology Corporation.
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
= (T
J(MAX)
= (125°C − 25°C) / (218.1°C/W) = 0.458W for
= (125°C − 25°C) / (120°C/W) = 0.833W for
0
SOT-23-5
J(MAX)
JA
. The Figure 2 of derating curves allows the
is the maximum junction temperature, T
A
= 25°C can be calculated by following
− T
25
JA
Ambient Temperature (°C)
A
) / θ
is 120°C/W on the standard JEDEC
WDFN-8L 2x2
JA
50
JA
JA
is layout dependent. For
is the junction to ambient
DS9724-02 July 2012
75
J(MAX)
Single Layer PCB
and thermal
100
JA
125
A
is
is