ADP1707 Analog Devices, ADP1707 Datasheet - Page 13

• Manufacturer Part Number: ADP1707
• Description: 1 A, Low Dropout, CMOS Linear Regulator with Tracking
• Manufacturer: Analog Devices

Thermal overload protection is included, which limits the
junction temperature to a maximum of 150°C (typical). Under
extreme conditions (that is, high ambient temperature and
power dissipation) when the junction temperature starts to
rise above 150°C, the output is turned off, reducing the output
current to zero. When the junction temperature drops below
135°C (typical), the output is turned on again and output
current is restored to its nominal value.
Consider the case where a hard short from OUT to ground
occurs. At first, the ADP1706/ADP1707/ADP1708 reach
current limit so that only 1.5 A is conducted into the short. If
self-heating of the junction becomes great enough to cause its
temperature to rise above 150°C, thermal shutdown activates,
turning off the output and reducing the output current to
zero. As the junction temperature cools and drops below
135°C, the output turns on and conducts 1.5 A into the short,
again causing the junction temperature to rise above 150°C.
This thermal oscillation between 135°C and 150°C causes a
current oscillation between 1.5 A and 0 A that continues as
long as the short remains at the output.
Current and thermal limit protections are intended to protect
the device against accidental overload conditions. For reliable
operation, device power dissipation should be externally limited
so junction temperatures do not exceed 125°C.
THERMAL CONSIDERATIONS
To guarantee reliable operation, the junction temperature of
the ADP1706/ADP1707/ADP1708 must not exceed 125°C. To
ensure that the junction temperature stays below this maximum
value, the user needs to be aware of the parameters that contrib-
ute to junction temperature changes. These parameters include
ambient temperature, power dissipation in the power device,
and thermal resistance between the junction and ambient air (θ
The θ
used and the amount of copper to which the GND pins of the
package are soldered on the PCB. Table 5 shows typical θ
of the 8-lead SOIC and 8-lead LFCSP for various PCB copper sizes.
Table 5. Typical θ
Copper Size (mm
0
50
100
300
500
1
Device soldered to minimum size pin traces.
1
JA
value is dependent on the package assembly compounds
2
JA
)
Values
θ
57.6
53.1
52.3
51.3
51.3
JA
(°C/W), SOIC
θ
61.2
59.7
59.4
65.9
62.3
JA
(°C/W), LFCSP
JA
values
Rev. 0 | Page 13 of 20
JA
).
The junction temperature of the ADP1706/ADP1707/ADP1708
can be calculated by
where:
T
P
where:
I
I
V
Power dissipation due to ground current is quite small and can
be ignored. Therefore, the junction temperature equation
simplifies to the following:
As shown in Equation 5, for a given ambient temperature,
input-to-output voltage differential, and continuous load
current, a minimum copper size requirement exists for the PCB
to ensure the junction temperature does not rise above 125°C.
Figure 36 to Figure 41 show junction temperature calculations
for different ambient temperatures, load currents, V
differentials, and areas of PCB copper.
LOAD
GND
D
A
IN
is the power dissipation in the die, given by
is the ambient temperature.
and V
is the ground current.
T
P
T
is the load current.
J
D
J
= T
= T
140
120
100
= [(V
80
60
40
20
0
0.5
OUT
A
A
Figure 36. 500 mm
+ (P
+ {[(V
MAX T
IN
are the input and output voltages, respectively.
1.0
– V
1mA
10mA
D
ADP1706/ADP1707/ADP1708
× θ
IN
OUT
J
(DO NOT OPERATE ABOVE THIS POINT)
1.5
– V
JA
) × I
)
OUT
100mA
300mA
2.0
LOAD
2
) × I
of PCB Copper, T
V
] + (V
IN
2.5
LOAD
– V
OUT
] × θ
IN
3.0
500mA
750mA
(V)
× I
JA
GND
3.5
}
A
= 25°C, SOIC
(LOAD CURRENT)
)
1A
4.0
IN
4.5
to V
5.0
OUT
(3)
(4)
(5)