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参数资料
| 型号： | ADP123-EVALZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 14/24页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION ADJUSTABLE V |
| 标准包装： | 1 |
| 每 IC 通道数： | 1 - 单 |
| 输出电压： | 0.8 ~ 5 V |
| 电流 - 输出： | 350mA |
| 输入电压： | 2.3 ~ 5.5 V |
| 稳压器类型： | 正，可调式 |
| 工作温度： | -40°C ~ 85°C |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | ADP123 |
ADP122/ADP123
CURRENT LIMIT AND THERMAL OVERLOAD
PROTECTION
Data Sheet
Table 6. Typical θ JA Values for Specified PCB Copper Sizes
θ JA (°C/W)
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.
Copper Size (mm 2 )
0 1
50
100
300
500
TSOT
170
152
146
134
131
LFCSP
255
164
138
109
80
Device soldered to narrow traces.
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
1
The typical Ψ JB values are 42.8°C/W for TSOT packages and
44.1°C/W for LFCSP packages.
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.
The junction temperature of the ADP122/ADP123 can be
calculated from the following equation:
T J = T A + ( P D × θ JA )
where:
T A is the ambient temperature.
P D is the power dissipation in the die, given by
P D = [( V IN ? V OUT ) × I LOAD ] + ( V IN × I GND )
(2)
(3)
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 JA ). The value
of θ JA is dependent on the package assembly compounds used
and the amount of copper to which the GND pins of the package
are soldered on the PCB. Table 6 shows typical θ JA values of the
5-lead TSOT package and 6-lead LFCSP package for various
where:
I LOAD is the load current.
I GND is the ground current.
V IN and V OUT are input and output voltages, respectively.
The power dissipation due to ground current is quite small and
can be ignored. Therefore, the junction temperature equation
can be simplified as follows:
T J = T A + {[( V IN ? V OUT ) × I LOAD ] × θ JA } (4)
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
through Figure 44 show junction temperature calculations for
different ambient temperatures, load currents, V IN to V OUT
differentials, and areas of PCB copper.
In cases where the board temperature is known, the thermal
characterization parameter, Ψ JB , can be used to estimate the jun-
ction temperature rise. The maximum junction temperature (T J ) is
calculated from the board temperature (T B ) and power dissipation
(P D ) using the formula
T J = T B + ( P D × Ψ JB ) (5)
PCB copper sizes.
Rev. E | Page 14 of 24
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