adm666aan Analog Devices, Inc., adm666aan Datasheet - Page 4

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

ADM663A/ADM666A
GENERAL INFORMATION
The ADM663A/ADM666A contains a micropower bandgap
reference voltage source; an error amplifier, A1; three compara-
tors, C1, C2, C3, and a series pass output transistor. A P-chan-
nel FET and an NPN transistor are used on the ADM663A
while the ADM666A uses an NPN output transistor.
CIRCUIT DESCRIPTION
The internal bandgap reference is trimmed to 1.3 V
This is used as a reference input to the error amplifier A1. The
feedback signal from the regulator output is supplied to the
other input by an on-chip voltage divider or by two external re-
sistors. When V
R1 and R2, provides the error amplifier’s feedback signal giving
a +5 V output. When V
tween R2 and R3 provides the error amplifier’s feedback signal
giving a +3.3 V output. When V
above ground and less than 50 mV below V
fier’s input is switched directly to the V
resistors are used to set the output voltage. The external resis-
tors are selected so that the desired output voltage gives 1.3 V
at V
Comparator C1 monitors the output current via the SENSE in-
put. This input, referenced to V
drop across a load sense resistor. If the voltage drop exceeds
0.5 V, then the error amplifier A1 is disabled and the output
current is limited.
The ADM663A has an additional amplifier, A2, which provides
a temperature proportional output, V
the inverting input of the error amplifier, a negative temperature
coefficient results at the output. This is useful when powering
liquid crystal displays over wide temperature ranges.
The ADM666A has an additional comparator, C4, that com-
pares the voltage on the low battery input, LBI, pin to the inter-
nal +1.3 V reference. The output from the comparator drives an
open drain FET connected to the low battery output pin, LBO.
The low battery threshold may be set using a suitable voltage
divider connected to LBI. When the voltage on LBI falls below
1.3 V, the open drain output LBO is pulled low.
SET
SHDN
GND
Figure 1. ADM663A Functional Block Diagram
.
V
IN
SET
is at ground, the internal divider tap between
A1
SET
R1
R3
R2
is at V
1.3V
OUT(2)
SET
D
E
C
O
D
E
R
0.9V
IN
, the internal divider tap be-
is at more than 50 mV
TC
ADM663A
, monitors the voltage
C2
C3
A2
SET
C1
. If this is summed into
50mV
V
pin, and external
IN
IN
–50mV
, the error ampli-
0.5V
V
V
SENSE
V
V
OUT2
OUT1
30 mV.
SET
TC
–4–
Both the ADM663A and the ADM666A contain a shutdown
(SHDN) input that can be used to disable the error amplifier
and hence the voltage output. The power consumption in shut-
down reduces to less than 9 A.
Circuit Configurations
For a fixed +5 V output the V
ternal resistors are necessary. This basic configuration is shown
in Figure 3. For a fixed +3.3 V output, the V
nected to V
ing utilized so the SENSE input is connected to V
Output Voltage Setting
If V
set according to the following equation:
where V
SET
SHDN
GND
Figure 2. ADM666A Functional Block Diagram
V
is not connected to GND or to V
SET
IN
+6V TO +16V
+4.5V TO +16V
IN
INPUT
= 1.30 V.
INPUT
as shown in Figure 4. Current limiting is not be-
Figure 4. A Fixed +3.3 V Output
Figure 3. A Fixed +5 V Output
V
A1
OUT
V
V
IN
ADM663A
ADM666A
R1
R2
R3
V
IN
ADM663A
ADM666A
V
SET
SET
V
1.3 V
SET
SET
GND
GND
D
E
C
O
D
E
R
1.3V
input is grounded and no ex-
ADM666A
(R1 R2)
SHDN
SENSE
V
SHDN
SENSE
V
OUT(2)
OUT(2)
C2
C3
R1
C4
C1
IN
50mV
V
, the output voltage is
IN
–50mV
SET
0.5V
input is con-
OUTPUT
OUTPUT
OUT(2)
+3.3V
+5V
V
LBI
SENSE
V
LBO
OUT
SET
.
REV. 0