ADP3307 Ver la hoja de datos (PDF) - Analog Devices
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ADP3307 Datasheet PDF : 8 Pages
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ADP3307
VIN
+
C1
1â®F
NR
ADP3307-3.3
IN
OUT
ERR
CNR
10nF
R1 330k†+
EOUT
VOUT = 3.3V
C2
4.7â®F
Shutdown Mode
Applying a high signal to the shutdown pin or tying it to the
input pin will turn the output ON. Pulling the shutdown pin
down to a low level or tying it to ground will turn the output
OFF. In shutdown mode, quiescent current is reduced to less
than 1 µA.
ON
OFF
Error Flag Dropout Detector
The ADP3307 will maintain its output voltage over a wide
SD
GND
range of load, input voltage and temperature conditions. If the
output is about to lose regulation, for example, by reducing the
Figure 3. Noise Reduction Circuit
supply voltage below the combined regulated output and drop-
Thermal Overload Protection
out voltages, the ERR pin will be activated. The ERR output is
The ADP3307 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
power dissipation), where die temperature starts to rise above
165°C, the output current is reduced until the die temperature
E 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
T 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
E Device power dissipation is calculated as follows:
PD = (VIN – VOUT) ILOAD + (VIN) IGND
L Where ILOAD and IGND are load current and ground current, VIN
and VOUT are input and output voltages respectively.
Assuming ILOAD= 100 mA, IGND= 2 mA, VIN = 5.5 V and
VOUT = 3.3 V, device power dissipation is:
O PD = (5.5 – 3.3) 0.1 + 5.5 × 2 mA = 0.231 W
∆T = TJ – TA = PD × θJA = 0.231 × 165 = 38°C
With a maximum junction temperature of 125°C, this yields a
maximum ambient temperature of 87°C.
S 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
B immediate vicinity of the package.
The following general guidelines will be helpful when designing
O a board layout:
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.
APPLICATIONS CIRCUITS
Crossover Switch
The circuit in Figure 4 shows that two ADP3307s 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 of the data sheet.
VIN = 4V TO 12V
OUTPUT SELECT
5V
0V
IN
OUT
ADP3307-2.7
SD
GND
VOUT = 2.7V/3.3V
C1 +
1.0â®F
IN
OUT
ADP3307-3.3
SD
GND
+ C2
0.47â®F
Figure 4. Crossover Switch
Higher Output Current
The ADP3307 can source up to 100 mA without any heatsink
or pass transistor. If higher current is needed, an appropriate
pass transistor can be used, as in Figure 5, to increase the out-
put current to 1 A.
1. PC board traces with larger cross section areas will remove
VIN = 4V TO 8V
MJE253*
VOUT = 3.3V@1A
more heat. For optimum results, use PC boards with thicker
copper and wider traces.
C1
47â®F
R1
50â€
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 ther-
mal resistance of the package.
IN
OUT
ADP3307-3.3
SD
ERR
GND
+ C2
10â®F
*AAVID531002 HEAT SINK IS USED
Figure 5. High Output Current Linear Regulator
REV. A
–7–
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