ADP3307
Shutdown Mode
NR
Applying a T T L 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 T T L low level or tying it to ground will turn the
output OFF. In shutdown mode, quiescent current is reduced
to less than 1 µA.
C
10nF
NR
ADP3307-3.3
V
IN
OUT
V
= 3.3V
IN
OUT
+
C2
4.7F
+
R1
330k
E
C1
1F
ERR
OUT
Er r or Flag D r opout D etector
ON
OFF
SD
T he ADP3307 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 drop-
out voltages, the ERR pin will be activated. T he ERR output is
an open collector that will be driven low.
GND
Figure 21. Noise Reduction Circuit
Ther m al O ver load P r otection
T he 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. Un-
der 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
has dropped to a safe level. Output current is restored when the
die temperature is reduced.
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.
AP P LICATIO NS CIRCUITS
Cr ossover Switch
T he circuit in Figure 22 shows that two ADP3307s can be used
to form a mixed supply voltage system. T he 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.
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 Tem per atur e
Device power dissipation is calculated as follows:
V
= 2.7V/3.3V
V
= 4V TO 12V
IN
OUT
OUT
IN
OUTPUT SELECT
PD = (VIN – VOUT) ILOAD + (VIN) IGND
4V
0V
ADP3307-2.7
SD
Where ILOAD and IGND are load current and ground current, VIN
and VOUT are input and output voltages respectively.
GND
Assuming ILOAD= 100 mA, IGND = 2 mA, VIN = 5.5 V and
VOUT = 3.3 V, device power dissipation is:
OUT
IN
+
+
C1
1.0F
C2
0.47F
PD = (5.5 – 3.3) 0.1 + 5.5 × 2 mA = 0.231 W
∆T = TJ – TA = PD × θJA = 0.231 × 165 = 38°C
ADP3307-3.3
SD
With a maximum junction temperature of 125°C, this yields a
maximum ambient temperature of ~72°C.
GND
P r inted Cir cuit Boar d Layout Consider ation
Figure 22. Crossover Switch
H igher O utput Cur r ent
T he 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 23, to increase the
output current to 1 A.
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.
T he following general guidelines will be helpful when designing
a board layout:
MJE253*
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.
V
= 3.3V@1A
V
= 4V TO 8V
OUT
IN
C1
47F
R1
50⍀
2. Increase the surface area exposed to open air so heat can be
removed by convection or forced air flow.
IN
OUT
+
C2
10F
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.
ADP3307-3.3
SD
ERR
GND
*AAVID531002 HEAT SINK IS USED
Figure 23. High Output Current Linear Regulator
REV. 0
–7–
5秒后页面跳转
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