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Revision 1.03

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AS1302

Datasheet - D e t a i l e d D e s c r i p t i o n

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

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

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:

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:

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.

(EQ 1)

η

P

OUT

P

IN

-------------

V

OUT

I

OUT

×

V

BATT

15I

OUT

,

×

-------------------------------------------

V

OUT

15V

,

BATT

-------------------------

==

=

(EQ 2)

η

P

OUT

P

IN

-------------

V

OUT

I

OUT

×

V

BATT

2I

OUT

×

-------------------------------------

V

OUT

2V

BATT

-------------------

==

=