ADP222ACPZ-1218-R7 AD [Analog Devices], ADP222ACPZ-1218-R7 Datasheet - Page 20

• Manufacturer Part Number: ADP222ACPZ-1218-R7
• Description: Dual, 300 mA Output, Low Noise
• Manufacturer: AD [Analog Devices]

ADP222/ADP223/ADP224/ADP225
CURRENT LIMIT AND THERMAL OVERLOAD
PROTECTION
The
damage due to excessive power dissipation by current and
thermal overload protection circuits. The ADP222/ADP223/
ADP224/ADP225
load reaches 300 mA (typical). When the output load exceeds
300 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 155°C (typical). Under
extreme conditions (that is, high ambient temperature and
power dissipation) when the junction temperature starts to rise
above 155°C, the output is turned off, reducing the output current
to 0. When the junction temperature drops below 140°C, the
output is turned on again, and output current is restored to its
nominal value.
Consider the case where a hard short from VOUTx to ground
occurs. At first, the
rent limits, so that only 300 mA is conducted into the short. If
self-heating of the junction is great enough to cause its tempera-
ture to rise above 155°C, thermal shutdown activates, turning
off the output and reducing the output current to 0 mA. As the
junction temperature cools and drops below 135°C, the output
turns on and conducts 300 mA into the short, again causing the
junction temperature to rise above 155°C. This thermal oscilla-
tion between 140°C and 155°C causes a current oscillation
between 300 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 against accidental overload conditions. For reliable
operation, device power dissipation must be externally limited
so that junction temperatures do not exceed 125°C.
ADP222/ADP223/ADP224/ADP225
Figure 71. Typical Turn-Off Time with and Without QOD Function
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
2000
are designed to current limit when the output
ADP222/ADP223/ADP224/ADP225
4000
TIME (µs)
ENABLE
V
V
OUT
OUT
, NO QOD
, WITH QOD
6000
are protected against
8000
10000
cur-
Rev. B | Page 20 of 24
THERMAL CONSIDERATIONS
In most applications, the
do not dissipate much heat due to its high efficiency. However,
in applications with high ambient temperature, and high supply
voltage to output voltage differential, the heat dissipated in
the package is large enough that it can cause the junction
temperature of the die to exceed the maximum junction
temperature of 125°C.
When the junction temperature exceeds 155°C, the converter
enters thermal shutdown. It recovers only after the junction
temperature has decreased below 140°C to prevent any permanent
damage. Therefore, thermal analysis for the chosen application
is very important to guarantee reliable performance over all
conditions. The junction temperature of the die is the sum of
the ambient temperature of the environment and the temperature
rise of the package due to the power dissipation, as shown in
Equation 2.
To guarantee reliable operation, the junction temperature of
the
125°C. To ensure that the junction temperature stays below this
maximum value, the user must be aware of the parameters that
contribute to junction temperature changes. These parameters
include ambient temperature, power dissipation in the power
device, and thermal resistances between the junction and ambient
air (θ
compounds that are used and the amount of copper used to
solder the package GND pin to the PCB.
Table 6 shows typical θ
various PCB copper sizes, and Table 7 shows the typical Ψ
of the 8-lead LFCSP.
Table 6. Typical θ
Copper Size (mm
25
100
500
1000
6400
1
Table 7. Typical Ψ
Model
8-Lead LFCSP
Device soldered to minimum size pin traces.
1
ADP222/ADP223/ADP224/ADP225
JA
). The θ
JA
number is dependent on the package assembly
2
JA
)
JB
Values
Value
JA
values of the 8-lead LFCSP package for
ADP222/ADP223/ADP224/ADP225
θ
175.1
135.6
77.3
65.2
51
Ψ
18.2
JA
JB
(°C/W)
(°C/W)
must not exceed
Data Sheet
JB
value