AS1349 Austin Semiconductor, AS1349 Datasheet - Page 10

• Manufacturer Part Number: AS1349
• Description: (AS1346 - AS1349) Dual Step Down Converter
• Manufacturer: Austin Semiconductor

AS1346, AS1347, AS1348, AS1349
Datasheet - D e t a i l e d D e s c r i p t i o n
When the top MOSFET is off, the bottom MOSFET is turned on until the inductor current starts to reverse as indicated
by the current reversal comparator, or the next clock cycle begins. The over-voltage detection comparator guards
against transient overshoots >7.8% by turning the main switch off and keeping it off until the transient is removed.
Short-Circuit Protection
The short-circuit protection turns off the power switches as long as the short is applied. When the short is removed the
device is continuing normal operation.
Dropout Operation
The AS1346, AS1347, AS1348, AS1349 is working with a low input-to-output voltage difference by operating at 100%
duty cycle. In this state, the PMOS is always on. This is particularly useful in battery-powered applications with a 3.3V
output.
The AS1346, AS1347, AS1348, AS1349 allows the output to follow the input battery voltage as it drops below the reg-
ulation voltage. The quiescent current in this state is reduced to a minimal value, which aids in extending battery life.
This dropout (100% duty-cycle) operation achieves long battery life by taking full advantage of the entire battery range.
The input voltage requires maintaining regulation and is a function of the output voltage and the load. The difference
between the minimum input voltage and the output voltage is called the dropout voltage. The dropout voltage is there-
fore a function of the on-resistance of the internal PMOS (R
proportional to the load current.
Note: At low V
Shutdown
Connecting EN to GND or logic low places the AS1346, AS1347, AS1348, AS1349 in shutdown mode and reduces the
supply current to 0.1µA. In shutdown the control circuitry and the internal NMOS and PMOS turn off and SW becomes
high impedance disconnecting the input from the output. The output capacitance and load current determine the volt-
age decay rate. For normal operation connect EN to V
Note: Pin EN should not be left floating.
Power-OK and Low-Battery-Detect Functionality
LBO goes low in startup mode as well as during normal operation if:
The LBI pin can be connected to a resistive-divider to monitor a particular definable voltage and compare it with a 1.2V
internal reference. If LBI is connected to GND
connected to the output. Therefore, the Power-OK functionality can be realised with no additional external
components.
The Power-OK feature is not active during shutdown. To obtain a logic-level output, connect a pull-up resistor from pin
LBO to pin V
perfect for most applications
For the circuit shown in the left of
value resistor-divider networks while maintaining accuracy. Place the resistor-divider network as close to the device as
possible. Use a defined resistor for R
Where:
V
www.austriamicrosystems.com/DC-DC_Step-Down/AS1346
LBI
- The voltage at the LBI pin is below LBI threshold (1.2V). This can be used to monitor the battery voltage.
- LBI pin is connected to GND and V
(the internal sense reference voltage) is 1.2V.
this case.
Therefore, power dissipation should be taken in consideration.
OUT
IN
or V
values, the R
DD
. Larger values for this resistor will help to minimize current consumption; a 100k Ω resistor is
(see Figure 18 on page
DS(ON)
Figure 18 on page
2
of the P-channel switch increases
and then calculate R
OUT1
is below 92.5% of its nominal value. LBO works as a power-OK signal in
(see Figure 1 on page 1)
R
1
=
11).
IN
11, the input bias current into LBI is very low, permitting large-
R
Revision 1.01
2
or logic high.
⋅
⎛
⎝
DS(ON)PMOS
1
---------- - 1
V
V
as:
LBI
IN
–
⎞
⎠
) and the inductor resistance (DCR) and this is
(see Electrical Characteristics on page
an internal resistive-divider is activated and
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(EQ 1)
4).
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