AS1364
Datasheet - Detailed Description
Output Voltage Selection
At the factory trimmed versions of the AS1364 offering the bypass pin (see Figure 1 on page 1), the output voltage is
then set to an internally trimmed voltage (see Ordering Information on page 14).
For the adjustable AS1364-AD, an output voltage between +1.2V and +5V can be set by using two external resistors
(see Figure 17). In this mode, VOUT is determined by:
R1
⎛
⎞
⎠
-----
VOUT = VSETBYP × 1 +
(EQ 1)
⎝
R2
Where:
VSET/BYP = +1.20V.
A simplification of R1 and R2 selection is:
VOUT
⎛
⎝
⎞
---------------------
R1 = R2 ×
– 1
(EQ 2)
⎠
VSETBYP
Since the input bias current at SET is less than 100nA, large resistance values can be used for R1 and R2 to minimize
power consumption and therefore increasing efficiency.
Note: Up to 125kΩ is acceptable for R2. If the SET pin is connected to GND without a resistor, 3.3V will be set as out-
put voltage.
In preset voltage mode, the impedance from SET to GND should be less than 10kΩ or spurious conditions may cause
the voltage at SET to exceed the 50mV threshold.
Figure 17. Adjustable Output Voltage Typical Application
3
5
IN
OUT
6
VIN
VOUT
COUT
4.7µF
4
IN
CIN
4.7µF
R1
R2
OUT
7
AS1364
2
On
Off
SET/BYP
EN
8
1
Reset Output
GND
POK
Shutdown
If pin EN is connected to GND the AS1364 is disabled. In shutdown mode all internal circuits are turned off, reducing
supply current to 10nA (typ). For normal device operation pin EN must be connected to IN. During shutdown, POK
goes low.
Power-OK
The AS1364 features a power-ok indicator that asserts when the output voltage falls out of regulation. The open-drain
POK output goes low when output voltage at OUT falls 6% below its nominal value. A 100kΩ pull-up resistor from POK
to a (typically OUT) provides a logic control signal.
POK can be used as a power-on-reset (POR) signal to a microcontroller or can drive an external LED to indicate a
power failure condition.
Note: POK is low during shutdown.
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