MAX667 Maxim, MAX667 Datasheet - Page 7

• Manufacturer Part Number: MAX667
• Description: +5V/Programmable Low-Dropout Voltage Regulator
• Manufacturer: Maxim

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.
The MAX667 can regulate currents as high as 250mA
and withstand input-output differential voltages as high
800
600
400
200
0
1
2
_______________________________________________________________________________________
3
V IN (V)
CIRCUIT OF
FIGURE 7
4
Power Dissipation
CIRCUIT OF
FIGURE 6
5
+5V/Programmable Low-Dropout
+5V/Programmable Low-Dropout
6
Figure 10. MAX667 Load Current vs. Input-Output Differential
Voltage
Figure 11. Output Response to +4V/100 s 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.
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
+5V OUTPUT
+2V/div
INPUT
+0.2V/div
400
300
200
100
+10V
+6V
0
Voltage Regulator
Voltage Regulator
0
DISSIPATION LIMIT
T
A
SO PACKAGE
= +50˚C
Operation from AC Sources
5
V IN- V OUT (V)
GUARANTEED 250mA
DIP PACKAGE
DISSIPATION LIMIT
1ms/div
10
15
7