ADP3300ART-2.7_00 查看數據表（PDF） - Analog Devices
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ADP3300ART-2.7_00 Datasheet PDF : 8 Pages
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ADP3300
Thermal Overload Protection
The ADP3300 is protected against damage due to excessive
power dissipation by its thermal overload protection circuit,
which limits the die temperature to a maximum of 165°C.
Under extreme conditions (i.e., high ambient temperature and
high power dissipation), where die temperature starts to rise
above 165°C, the output current is reduced until die tempera-
ture has dropped to a safe level. Output current is restored when
the die temperature is reduced.
Current and thermal limit protections are intended to protect
the device against accidental overload conditions. For normal
operation, device power dissipation should be externally limited
so that junction temperatures will not exceed 125°C.
Calculating Junction Temperature
Device power dissipation is calculated as follows:
PD = (VIN – VOUT) ILOAD + (VIN) IGND
Where ILOAD and IGND are load current and ground current, VIN
and VOUT are input and output voltages respectively.
Assuming ILOAD = 50 mA, IGND = 0.5 mA, VIN = 8 V and
VOUT = 3.3 V, device power dissipation is:
PD = (8 – 3.3) 0.05 + 8 × 0.5 mA = 0.239 W
∆T = TJ – TA = PD × θJA = 0.239 × 165 = 39.4°C
With a maximum junction temperature of 125°C, this yields a
maximum ambient temperature of 85°C.
Printed Circuit Board Layout Consideration
Surface mount components rely on the conductive traces or
pads to transfer heat away from the device. Appropriate PC
board layout techniques should be used to remove heat from the
immediate vicinity of the package.
The following general guidelines will be helpful when designing
a board layout:
1. PC board traces with larger cross section areas will remove
more heat. For optimum results, use PC boards with thicker
copper and wider traces.
2. Increase the surface area exposed to open air so heat can be
removed by convection or forced air flow.
3. Do not use solder mask or silkscreen on the heat dissipating
traces because it will increase the junction to ambient thermal
resistance of the package.
Shutdown Mode
Applying a TTL high signal to the shutdown pin or tying it to
the input pin will turn the output ON. Pulling the shutdown pin
down to 0.3 V or below, or tying it to ground, will turn the
output OFF. In shutdown mode, quiescent current is reduced
to less than 1 µA.
Error Flag Dropout Detector
The ADP3300 will maintain its output voltage over a wide
range of load, input voltage and temperature conditions. If the
output is about to lose regulation, for example, by reducing the
supply voltage below the combined regulated output and dropout
voltages, the ERR pin will be activated. The ERR output is an
open collector that will be driven low.
Once set, the ERRor flag’s hysteresis will keep the output low
until a small margin of operating range is restored either by
raising the supply voltage or reducing the load.
APPLICATION CIRCUITS
Crossover Switch
The circuit in Figure 22 shows that two ADP3300s can be used
to form a mixed supply voltage system. The output switches
between two different levels selected by an external digital input.
Output voltages can be any combination of voltages from the
Ordering Guide.
VIN = 5.5V TO 12V
OUTPUT SELECT
5.0V
0V
IN
OUT
ADP3300-5.0
GND
VOUT = 5V/3.3V
C1
1.0 F
IN
OUT
ADP3300-3.3
GND
C2
0.47 F
Figure 22. Crossover Switch
Higher Output Current
If higher current is needed, an appropriate pass transistor can be
used, as in Figure 23, to increase the output current to 1 A.
VIN = 6V TO 8V
C1
47 F
MJE253*
R1
50Ω
VOUT = 5V @ 1A
IN
OUT
ADP3300-5
C2
10 F
GND
*AAVID531002 HEAT SINK IS USED
Figure 23. High Output Current Linear Regulator
REV. A
–7–
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