ADM666AAN データシートの表示（PDF） - Analog Devices
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ADM666AAN Datasheet PDF : 9 Pages
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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 ± 30 mV.
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 VSET is at ground, the internal divider tap between
R1 and R2, provides the error amplifier’s feedback signal giving
a +5 V output. When VSET is at VIN, the internal divider tap be-
tween R2 and R3 provides the error amplifier’s feedback signal
giving a +3.3 V output. When VSET is at more than 50 mV
above ground and less than 50 mV below VIN, the error ampli-
fier’s input is switched directly to the VSET pin, and external
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 VSET.
Comparator C1 monitors the output current via the SENSE in-
put. This input, referenced to VOUT(2), monitors the voltage
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, VTC. If this is summed into
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.
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 µA.
VIN
VOUT
1.3 V
A1
0.5V
C1
SEN SE
SHDN
GND
D
E
C2 VIN–50mV
C
O
VSET
D
E
C3
R
50mV
R1
LBI
1.3V C4
R2
LBO
R3
ADM666A
Figure 2. ADM666A Functional Block Diagram
Circuit Configurations
For a fixed +5 V output the VSET input is grounded and no ex-
ternal resistors are necessary. This basic configuration is shown
in Figure 3. For a fixed +3.3 V output, the VSET input is con-
nected to VIN as shown in Figure 4. Current limiting is not be-
ing utilized so the SENSE input is connected to VOUT(2).
+6V TO +16V
INPUT
VIN
ADM663A
ADM666A
SENSE
VOUT(2)
VSET GND SHDN
+5V
OUTPUT
Figure 3. A Fixed +5 V Output
VIN
SHDN
GND
1.3V
A1
VOUT2
VOUT1
0.5V
C1
SEN SE
D
E
C2 VIN–50mV
C
O
D
E
C3
VSET
R
50mV
R1
R2
0.9V A2
VTC
R3
ADM663A
Figure 1. ADM663A Functional Block Diagram
+4.5V TO +16V
INPUT
VIN
ADM663A
ADM666A
SENSE
VOUT(2)
VSET GND SHDN
+3.3V
OUTPUT
Figure 4. A Fixed +3.3 V Output
Output Voltage Setting
If VSET is not connected to GND or to VIN, the output voltage is
set according to the following equation:
V OUT
= V SET
× (R1 + R2)
R1
where VSET = 1.30 V.
–4–
REV. 0
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