ADP123-EVALZ Analog Devices Inc, ADP123-EVALZ Datasheet - Page 14

• Manufacturer Part Number: ADP123-EVALZ
• Description: Linear Regulator Eval. Board
• Manufacturer: Analog Devices Inc

Specifications of ADP123-EVALZ

• Silicon Manufacturer: Analog Devices
• Application Sub Type: LDO
• Kit Application Type: Power Management - Voltage Regulator
• Silicon Core Number: ADP123
• Kit Contents: Board, Starter Guide
• Channels Per Ic: 1 - Single
• Voltage - Output: 0.8 ~ 5 V
• Current - Output: 350mA
• Voltage - Input: 2.3 ~ 5.5 V
• Regulator Type: Positive Adjustable
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: ADP123
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADP122/ADP123
CURRENT LIMIT AND THERMAL OVERLOAD
PROTECTION
The ADP122/ADP123 are protected from damage due to excessive
power dissipation by current and thermal overload protection
circuits. The ADP122/ADP123 are designed to limit the current
when the output load reaches 500 mA (typical). When the output
load exceeds 500 mA, the output voltage is reduced to maintain
a constant current limit.
Thermal overload protection is included, which limits the junction
temperature to a maximum of 150°C typical. Under extreme con-
ditions (that is, high ambient temperature and power dissipation),
when the junction temperature starts to rise above 150°C, the
output is turned off, reducing output current to zero. When the
junction temperature cools to less than 135°C, the output is turned
on again and the output current is restored to its nominal value.
Consider the case where a hard short from VOUT to GND occurs.
At first, the ADP122/ADP123 limit the current so that only 500 mA
is conducted into the short. If self-heating causes the junction
temperature to rise above 150°C, thermal shutdown activates,
turning off the output and reducing the output current to zero.
When the junction temperature cools to less than 135°C, the
output turns on and conducts 500 mA into the short, again
causing the junction temperature to rise above 150°C. This
thermal oscillation between 135°C and 150°C results in a current
oscillation between 500 mA and 0 mA that continues as long as
the short remains at the output.
Current and thermal limit protections are intended to protect the
device from damage due to accidental overload conditions. For
reliable operation, the device power dissipation must be externally
limited so that the junction temperature does not exceed 125°C.
THERMAL CONSIDERATIONS
To guarantee reliable operation, the junction temperature of the
ADP122/ADP123 must not exceed 125°C. To ensure that the
junction temperature is less than this maximum value, the user
needs to be aware of the parameters that contribute to junction
temperature changes. These parameters include ambient tem-
perature, power dissipation in the power device, and thermal
resistances between the junction and ambient air (θ
of θ
and the amount of copper to which the GND pins of the package
are soldered on the PCB. Table 6 shows typical θ
5-lead TSOT package for various PCB copper sizes.
Table 6. Typical θ
1
The typical Ψ
Device soldered to narrow traces.
Copper Size (mm
0
50
100
300
500
1
JA
is dependent on the package assembly compounds used
JB
value is 42.8°C/W.
JA
2
)
Values for Specified PCB Copper Sizes
θ
170
152
146
134
131
JA
(°C/W)
JA
JA
values of the
). The value
Rev. 0 | Page 14 of 20
The junction temperature of the ADP122/ADP123 can be
calculated from the following equation:
where:
T
P
where:
I
I
V
The power dissipation due to ground current is quite small and
can be ignored. Therefore, the junction temperature equation
can be simplified as follows:
As shown in Equation 4, for a given ambient temperature, input-
to-output voltage differential, and continuous load current, there
exists a minimum copper size requirement for the PCB to ensure
that the junction temperature does not rise above 125°C. Figure 34
through Figure 40 show junction temperature calculations for
different ambient temperatures, load currents, V
differentials, and areas of PCB copper.
In cases where the board temperature is known, the thermal
characterization parameter, Ψ
ction temperature rise. The maximum junction temperature (T
calculated from the board temperature (T
(P
LOAD
GND
D
A
IN
D
is the ambient temperature.
is the power dissipation in the die, given by
) using the formula
and V
is the ground current.
T
P
T
T
is the load current.
D
J
J
J
= T
= T
= T
= [(V
OUT
A
A
B
+ (P
+ (P
+ {[(V
IN
are input and output voltages, respectively.
− V
D
D
× Ψ
× θ
IN
OUT
− V
JA
) × I
JB
)
)
OUT
LOAD
) × I
JB
] + (V
, can be used to estimate the jun-
LOAD
] × θ
IN
× I
B
JA
) and power dissipation
GND
}
)
IN
to V
OUT
J
) is
(2)
(3)
(4)
(5)