MAX667(1994) Просмотр технического описания (PDF) - Maxim Integrated
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MAX667 Datasheet PDF : 8 Pages
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+5V/Programmable Low-Dropout
Voltage Regulator
800
CIRCUIT OF
600
FIGURE 7
400
TA = +50˚C
300
GUARANTEED 250mA
400
CIRCUIT OF
FIGURE 6
200
0
1
2
3
4
5
6
VIN (V)
200
DIP PACKAGE
DISSIPATION LIMIT
100
SO PACKAGE
DISSIPATION LIMIT
0
0
5
10
15
VIN-VOUT (V)
Figure 9. Quiescent Current Below Dropout with Connections
of Figures 6 and 7
PNP transistor is turned on fully as regulation is lost.
Even with a load current of a few microamperes, the
base current will be driven above 5mA. Figure 8 shows
how this base current may be significant.
Consequently, a mostly discharged battery can be fur-
ther discharged at end-of-life.
Figure 6 shows how this condition can be modified by
connecting DD to SHDN with a 47kΩ resistor, R1, par-
alleled with a 0.1µF capacitor to GND. This modifica-
tion reduces the no-load quiescent current to
approximately 160µA when dropout is reached (Figure
9), but increases the dropout voltage by about 0.1V.
The output voltage drops to approximately 3V once DD
begins to activate SHDN, but it does not fall to zero
because SHDN is only partially activated.
A second alternate connection (Figure 7) further
reduces quiescent current near the dropout voltage,
compared to the circuit in Figure 6. The output must be
set with external resistors (R1, R2), so DD lowers the
output voltage as the input voltage falls by sourcing
current into SET via R3. Quiescent current remains low
for inputs down to 3.5V, and peaks before falling to 0
at low input voltages. Although the current peak is
higher than with the connection in Figure 6, this may
be more useful because the quiescent current peaks
at an input voltage well below the useful range of most
batteries (Figure 9). Also, as IN falls below 5V, OUT
tracks IN minus the dropout voltage. This connection
still allows separate use of the SHDN input.
Power Dissipation
The MAX667 can regulate currents as high as 250mA
and withstand input-output differential voltages as high
Figure 10. MAX667 Load Current vs. Input-Output Differential
Voltage
+10V
INPUT
+2V/div
+6V
+5V OUTPUT
+0.2V/div
1ms/div
Figure 11. Output Response to +4V/100µs Input Step
as 15.2V, but not simultaneously. The maximum power
dissipation is dependent on the package and the tem-
perature (see Absolute Maximum Ratings). Figure 10
shows the maximum output current at various input-
output differential voltages for the plastic DIP and SO
packages. The MAX667 can withstand short-circuit
loads up to 1 second.
Operation from AC Sources
The MAX667 is a micropower CMOS regulator intend-
ed principally for battery operation. When operating
from AC sources, consider power-supply ripple rejec-
tion. The MAX667’s error amplifier produces very low
gain bandwidth, and the input power-supply rejection
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