ADM666 Просмотр технического описания (PDF) - Analog Devices
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ADM666 Datasheet PDF : 6 Pages
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ADM663/ADM666
VIN
VOUT
ADM666
0.5V
C1
SENSE
SHDN
GND
A1
50mV
C2
VSET
LBI
LBO
C3
1.3V
REF
Figure 2. ADM666 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. Current limiting is not being utilized so the SENSE
input is connected to VOUT(2). The input voltage can range from
+6 V to +16 V and output currents up to 40 mA are available
provided that the maximum package power dissipation is not
exceeded.
+6V TO +16V
INPUT
VIN
ADM663
ADM666
SENSE
VOUT(2)
GND VSET SHDN
+5V
OUTPUT
Figure 3. ADM663/ADM666 Fixed +5 V Output
Output Voltage Setting
If VSET is not connected to GND, the output voltage is set ac-
cording to the following equation.
V OUT
= V SET
×
R1 + R2
R1
where V SET
= 1. 30V
The resistor values may be selected by firstly choosing a
value for R1 and then selecting R2 according to the following
equation.
R2 = R1 × V1.O3U0T – 1
The input leakage current on VSET is 10 nA maximum. This al-
lows large resistor values to be chosen for R1 and R2 with little
degradation in accuracy. For example, a 1 MΩ resistor may be
selected for R1 and then R2 may be calculated accordingly.
The tolerance on VSET is guaranteed at less than ± 30 mV so in
most applications, fixed resistors will be suitable.
+2V TO +16V
INPUT
VIN
ADM663
ADM666
SHDN
GND
SENSE
VOUT(2)
RCL
VSET
+1.3V TO +15V
OUTPUT
R2
R1
Figure 4. ADM663/ADM666 Adjustable Output
Current Limiting
Current limiting may be achieved by using an external current
sense resistor in series with VOUT(2). When the voltage across
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.
RCL
=
0. 5
ICL
where RCL is the current sense resistor, ICL is the maximum
current limit.
The value chosen for RCL should also ensure that the current is
limited to less than the 50 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 which must be considered
when determining the regulators dropout voltage.
If current limiting is not used, the SENSE input should be con-
nected to VOUT(2).
Shutdown Input (SHDN)
The SHDN input allows the regulator to be switched off with a
logic level signal. This will disable the output and reduce the
current drain to a low quiescent (12 µA 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 SHDN should
be connected to GND.
Low Supply or Low Battery Detection
The ADM666 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.
R3 = R4 × V1B.A3T0T – 1
where R3 and R4 are the resistive divider resistors and VBATT is
the desired low voltage threshold.
–4–
REV. 0
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