ADM666 Просмотр технического описания (PDF) - Analog Devices
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ADM666 Datasheet PDF : 6 Pages
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ADM663/ADM666
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 MΩ for
R3 and 2.7 MΩ for R4.
+2V TO +16V
INPUT
R3
R4
VIN
SENSE
RCL
ADM666
VOUT
LBI
SHDN GND
VSET
LBO
LOW
BATTERY
OUTPUT
+1.3V TO +15V
OUTPUT
R2
R1
Figure 5. ADM666 Adjustable Output with Low Battery
Detection
High Current Operation
The ADM663 contains an additional output, VOUT1, suitable
for directly driving the base of an external NPN transistor. Fig-
ure 6 shows a configuration which can be used to provide +5 V
with boosted current drive. A 1 Ω current sensing resistor limits
the current at 0.5 A.
VIN
+
10µ F
SHUTDOW N
VIN
ADM663
VOUT1
VOUT2
SHDN
2N 4237
100Ω
1.0Ω
VSET
GND
SENSE
+
10µF
+5V, 0.5A
OUTPUT
Figure 6. ADM663 Boosted Output Current (0.5 A)
Temperature Proportional Output
The ADM663 contains a VTC output with a positive tempera-
ture coefficient of +2.5 mV/°C. This may be connected to the
summing junction of the error amplifier (VSET) through a resis-
tor resulting in a negative temperature coefficient at the output
of the regulator.
This is especially useful in multiplexed LCD displays to com-
pensate for the inherent negative temperature coefficient of the
LCD threshold. At 25°C the voltage at the VTC output is typi-
cally 0.9 V. The equations for setting both the output voltage
and the tempco are given below. If this function is not being
used, then VTC should be left unconnected.
SENSE
VOUT2
ADM663
VSET
VTC
VOUT
R2
R3
R1
Figure 7. ADM663 Temperature Proportional Output
( ) VOUT
= V SET
× 1 +
R2
R1
+
R2 ×
R3
V SET
– V TC
TCV OUT
=
– R2
R3
× TVCTC
where V SET = +1. 3V , VTC = +0.9V , TCV TC = +2.5 mV /°C
APPLICATION HINTS
Input-Output (Dropout Voltage)
A regulator’s minimum input-output differential or dropout
voltage determines the lowest input voltage for a particular out-
put voltage. The ADM663/ADM666 dropout voltage is 0.8 V at
its rated output current. For example when used as a fixed +5 V
regulator the minimum input voltage is +5.8 V. At lower output
currents, (IOUT < 5 mA), on the ADM663, VOUT1 may be used
as the output driver in order to achieve lower dropout voltages.
Please refer to Figure 9. In this case the dropout voltage de-
pends on the voltage drop across the internal FET transistor.
This may be calculated by multiplying the FET’s saturation re-
sistance by the output current. As the current limit circuitry is
referenced to VOUT2, VOUT2 should be connected to VOUT1. For
high current operation VOUT2 should be used alone and VOUT1
left unconnected.
Bypass Capacitors
The high frequency performance of the ADM663/ADM666
may be improved by decoupling the output using a filter capaci-
tor. A capacitor value of 10 µF is suitable.
An input capacitor helps reduce noise and improves dynamic
performance. A suitable input capacitor of 0.1 µF or greater
may be used.
REV. 0
–5–
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