adm666aan Analog Devices, Inc., adm666aan Datasheet - Page 5

• Manufacturer Part Number: adm666aan
• Description: Tri-mode +3.3 V, +5 V, Adjustable Micropower Linear Voltage Regulators
• Manufacturer: Analog Devices, Inc.

REV. 0
The resistor values may be selected by first choosing a value for
R1 and then selecting R2 according to the following equation:
The input leakage current on V
lows large resistor values to be chosen for R1 and R2 with little
degradation in accuracy. For example, a 1 M resistor may be
selected for R1, and then R2 may be calculated accordingly.
The tolerance on V
most applications, fixed resistors will be suitable.
Current Limiting
Current limiting may be achieved by using an external current
sense resistor in series with V
the sense resistor exceeds the internal 0.5 V threshold, current
limiting is activated. The sense resistor is therefore chosen such
that the voltage across it will be 0.5 V when the desired current
limit is reached.
where R
current limit.
The value chosen for R
limited to less than the 100 mA absolute maximum rating and
also that the power dissipation will also be within the package
maximum ratings.
If current limiting is employed, there will be an additional volt-
age drop across the sense resistor that must be considered when
determining the regulators dropout voltage.
If current limiting is not used, the SENSE input should be con-
nected to V
Shutdown Input (SHDN)
The SHDN input allows the regulator to be turned off with a
logic level signal. This will disable the output and reduce
+2V TO +16V
CL
INPUT
OUT(2)
is the current sense resistor, I
Table I. Output Voltage Selection
Figure 5. Adjustable Output
.
V
SHDN
SET
V
GND
V
R1/R2
IN
ADM663A
ADM666A
R2
IN
SET
is guaranteed at less than 30 mV so in
CL
GND
should also ensure that the current is
R1
R
CL
OUT(2)
SET
SENSE
V
V
1.30
OUT(2)
0.5
I
V
OUT
is 10 nA maximum. This al-
CL
V
+5 V
+3 V
ADJ
SET
. When the voltage across
OUT
R
1
CL
CL
is the maximum
+1.3V TO +15V
OUTPUT
R2
R1
–5–
the current drain to a low quiescent (9 A maximum) current.
This is very useful for low power applications. The SHDN input
should be driven with a CMOS logic level signal since the input
threshold is 0.3 V. In TTL systems, an open collector driver
with a pull-up resistor may be used.
If the shutdown function is not being used, then it should be
connected to GND.
Low Supply or Low Battery Detection
The ADM666A contains on-chip circuitry for low power supply
or battery detection. If the voltage on the LBI pin falls below the
internal 1.3 V reference, then the open drain output LBO will
go low. The low threshold voltage may be set to any voltage
above 1.3 V by appropriate resistor divider selection.
where R3 and R4 are the resistive divider resistors and V
the desired low voltage threshold.
Since the LBI input leakage current is less than 10 nA, large val-
ues may be selected for R3 and R4 in order to minimize loading.
For example, a 6 V low threshold may be set using 10 M for
R3 and 2.7 M
High Current Operation
The ADM663A contains an additional output, V
for directly driving the base of an external NPN transistor. Fig-
ure 7 shows a configuration which can be used to provide +5 V
with boosted current drive. A 1
the current at 0.5 A.
Figure 6. ADM666A Adjustable Output with Low Battery
Detection
+2V TO +16V
INPUT
Figure 7. ADM663A Boosted Output Current (0.5 A)
SHUTDOWN
V
10 F
IN
R3
R4
+
for R4.
V
SHDN
LBI
IN
ADM666A
SHDN
R3
V
SET
ADM663A
GND
V
IN
R4
GND
ADM663A/ADM666A
SENSE
V
1.3 V
V
V
LBO
BATT
OUT
SET
current sensing resistor limits
SENSE
V
V
OUT1
OUT2
LOW
BATTERY
OUTPUT
10 F
1
R
CL
100
+
+1.3V TO +15V
OUTPUT
R2
R1
OUT1
+5V, 0.5A
OUTPUT
2N4237
1.0
, suitable
BATT
is