L6924UTR datasheet(15/37 Pages) STMICROELECTRONICS

No. de pieza	L6924UTR

Descripción Electrónicos	USB compatible battery charger system with integrated power switch for Li-Ion/Li-Polymer

PDF	37 Pages

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Fabricante Electrónico	STMICROELECTRONICS [STMicroelectronics]

Página de inicio	http://www.st.com

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15 / 37 page

L6924U

Operation description

Doc ID 14716 Rev 2

15/37

Where

ΔV

MOS is given by:

Equation 3

Where,

ILIM = current limit of the wall adapter, and RDS(on) = resistance of the power MOSFET.

The difference between the programmed charge current and the adapter limit should be

high enough to minimize the RDS(on) value (and the power dissipation). This makes the

control loop completely unbalanced and the power element is fully turned on.

Figure 8

shows the RDS(on) values for different output voltages and charging currents for an

adapter current limit of 500 mA.

Figure 8.

RDS(on) curves vs. charging current and output voltage

Neglecting the voltage drop across the charger (

ΔV

MOS) when the device operates in this

condition, its input voltage is equal to the battery one, and so a very low operating input

voltage (down to 2.5 V) is required. The power dissipated by the device during this phase is:

Equation 4

When the battery voltage approaches the final value, the charger gets back the control of

the current, reducing it. Due to this, the upstream adapter exits the current limit condition

and its output goes up to the regulated voltage VADP. This is the worst case in power

dissipation:

LIM

)

(

MOS

LIM

)

(

L6924UTR Datasheet(PDF) 15 Page - STMicroelectronics