Operation description

STNS01

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DocID024654 Rev 2

8

Operation description

The STNS01 is a power management IC integrating a battery charger with power path

function, battery protection circuitry, battery temperature monitoring and a 3.1 V 100 mA

LDO.

When a valid input voltage (V

IN

) is present on the IN pin, after security checks are

performed, the battery charger starts charging the battery using a constant-current/constant-

voltage charging algorithm.

The input voltage (V

IN

) is considered to be valid if it is higher than V

UVLO

and lower than

V

INOVP

.

The power path architecture allows charging the battery and supplying the system at the

same time. When the input voltage is not valid, the LDO (and every external IC connected to

SYS) is supplied by the battery through a low resistance path.

The device also provides protection to the battery against the following fault conditions:

–

overcharge

–

overdischarge

–

charge overcurrent

–

discharge overcurrent

If a fault condition is detected while the input voltage is valid (V

UVLO

< V

IN

< V

INOVP

), the

CHG pin starts toggling to inform the control logic that an error occurred.

The device can also be put in reduced battery drain mode (shutdown, I

BAT

< 500 nA) to

maximize battery life during end-product shipping and shelf time.

8.1

Power-on

When the device is in shutdown mode, the pins LDO and SYS are not supplied. In order to

turn the device on a valid input voltage must be connected (V

IN

).

The CEN pin must be floating or tied high during power-on for proper operation.

8.2

Battery charger

The STNS01's battery charger is designed to charge single cell Li-Ion batteries up to 4.2 V

using a CC-CV charging algorithm (see

Figure 6). When a valid input voltage is detected,

the STNS01 starts the charge cycle and the CHG pin switches from high impedance to low

level.

The charging process starts if the battery voltage is higher than V

BATMIN

. If the battery is

deeply discharged (the battery voltage is lower than V

PRE

and higher than V

BATMIN

) the

charger enters the pre-charge phase and starts charging in constant-current mode using a

low current (I

PRE

= 20% I

FAST

). If the battery voltage does not reach the V

PRE

threshold

within t

PRE

, the charging process is stopped and a fault is signaled.

When the battery voltage reaches the V

PRE

threshold, the constant-current fast-charge

phase is entered and the charging current is increased to I

FAST

. The value of I

FAST

can be

programmed from 15 mA to 200 mA using an external resistor as described in the I

SET

pin

description (

Section 7).