ADP667
Shutdown Input (SHDN)
APPLICATIONS INFORMATION
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 (1 µA maximum) current. This
is very useful for low power applications. Driving the SHDN in-
put to greater than 1.5 V places the part in shutdown.
Circuit Configurations
For a fixed +5 V output the SET input should be grounded, and
no external resistors are necessary. This basic configuration is
shown in Figure 2. The input voltage can range from +5.15 V
to +16.5 V, and output currents up to 250 mA are available
provided that the maximum package power dissipation is not
exceeded.
If the shutdown function is not being used, then SHDN should
be connected to GND.
Low Supply or Low Battery Detection
+5V
OUTPUT
The ADP667 contains on-chip circuitry for low power supply or
battery detection. If the voltage on the LBI pin falls below the
internal 1.255 V reference, then the open drain output LBO will
go low. The low threshold voltage may be set to any voltage
above 1.255 V by appropriate resistor divider selection.
OUT
IN
+
+
C1
10µF
ADP667
SET GND SHDN
VBATT
VLBI
R3 = R4 ×
–1
Figure 2. Fixed +5 V Output Circuit
Output Voltage Setting
If the SET input is connected to a resistor divider network, the
output voltage is set according to the following equation:
where R3 and R4 are the resistive divider resistors and VBATT is
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 MΩ for
R3 and 2.7 MΩ for R4.
R1+ R2
VOUT =VSET
where VSET = 1.255 V.
×
R1
The LBO output is an open-drain output that goes low sinking
current when LBI is less than 1.255 V. A pull-up resistor of
10 kΩ or greater may be used to obtain a logic output level with
V
IN
IN
the pull-up resistor connected to VOUT
.
OUT
SET
V
OUT
+
C1
10µF
ADP667
R2
V
IN
IN
OUT
V
OUT
R3
R4
+
R1
C1
10µF
ADP667
10kΩ
SHDN
GND
LBI
LBO
LOW BATTERY
STATUS OUTPUT
SHDN GND SET
Figure 3. Adjustable Output Circuit
The resistor values may be selected by first choosing a value for
R1 and then selecting R2 according to the following equation:
Figure 4. Low Battery/Supply Detect Circuit
VOUT
VSET
R2 = R1×
−1
The input leakage current on SET is 10 nA maximum. This
allows 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 accord-
ingly. The tolerance on SET is guaranteed at less than ±25 mV,
so in most applications fixed resistors will be suitable.
–4–
REV. 0
ADI [ ADI ]
