AS1302
Datasheet - Detailed Description
Soft-start
The soft-start circuit prevents the supply from high inrush currents caused by the converter’s power-up sequence.
During the soft-start (0.5ms typ) the device limits the inrush current. The device is capable to power-up at the minimum
specified battery voltage and with the maximum load (ohmic equivalent) applied to the output.
Undervoltage Lockout, UVLO
The AS1302 is equipped with an undervoltage lockout functionality. If the battery voltage drops below 2.5V (typ) the
device enters the undervoltage lockout condition. The device remains in this condition until the battery voltage is high
enough to enter the soft start sequence. An internal hysteresis of 300mV prevents ringing during startup. If the input
voltage increases to 2.8V (typ) again after such a condition the device turns-on automatically.
Shutdown Mode
The AS1302 enters low-power shutdown mode when EN is set to logic low. In shutdown the charge-pump action is
halted, the output is completely disconnected from the input and VOUT will drop to 0V.
Note: For a stable operation trigger at least a rising edge on the EN pin to set the internal settings of the device after
VBATT power-up.
Short-Circuit Protection
Short-circuit protection prevents damage to the device if the output is shorted to ground. Whenever the output voltage
is pulled significantly below VBATT, short-circuit protection is triggered and limits the current. As soon as VOUT recovers
the protection is released and the device enters soft-start mode.
Thermal Shutdown
The AS1302 offers thermal shutdown, which prevents damage due to an over-temperature condition. Thermal
shutdown will be initiated if the junction temperature exceeds 145°C. If the temperature drops below this value, the
thermal shutdown will be released automatically and the device resumes operation. A hysteresis prevents the thermal
shutdown from oscillating.
Efficiency Consideration
In the 2:3 operation mode the input current of the charge pump is approximately 1.5x the load current. In an ideal
charge pump the efficiency can be calculated by:
POUT
-------------
PIN
VOUT × IOUT
-------------------------------------------
VBATT × 1, 5IOUT
VOUT
------------------------
1, 5VBATT
η =
=
=
(EQ 1)
The same works for the 1:2 operation mode. The input current of the charge pump is approximately 2x the load
current. The efficiency of a charge pump in 1:2 operation mode can be calculated by:
POUT
-------------
PIN
VOUT × IOUT
-------------------------------------
VBATT × 2IOUT
VOUT
------------------
2VBATT
η =
=
=
(EQ 2)
For typical and high output power conditions the quiescent current and the switching losses are negligible and (EQ 1)
and (EQ 2) are valid. Hence, with the same input Voltage the 2:3 operation mode will result into a higher efficiency than
the 1:2 operation mode.
www.austriamicrosystems.com/DC-DC_Step-Up/AS1302
Revision 1.03
12 - 18
AMSCO [ AMS(艾迈斯) ]
