TPS65021 datasheet(39/45 Pages) TI

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OUT

DEFDCDC3

R1 * R2

OUT

DEFDCDC3

+ R2

(8)

VRTC Output

LDO1 and LDO2

Trespwron

Vcc-Filter

TPS65021

SLVS613 – OCTOBER 2005

When a resistor divider is connected to DEFDCDCx, the output voltage can be set from 0.6 V up to the input

voltage V(bat). The total resistance (R1+R2) of the voltage divider should be kept in the 1-MR range in order to

maintain a high efficiency at light load.

V(DEFDCDCx) = 0.6 V

The VRTC output is typically connected to the Vcc_Batt pin of a Intel PXA270 processor. During power-up of the

processor, the TPS65021 internally switches from the LDO or the backup battery to the system voltage

connected at the VSYSIN pin (see Figure 25). It is recommended to add a capacitor of 4.7-

µF minimum to the

VRTC pin.

The LDOs in the TPS65021 are general-purpose LDOs which are stable using ceramics capacitors. The

minimum output capacitor required is 2.2

µF. The LDOs output voltage can be changed to different voltages

between 1 V and 3.3 V using the I2C interface. Therefore, they can also be used as general-purpose LDOs in

applications powering processors different from PXA270. The supply voltage for the LDOs needs to be

connected to the VINLDO pin, giving the flexibility to connect the lowest voltage available in the system and

provides the highest efficiency.

This is the input to a capacitor that defines the reset delay time after the voltage at VRTC rises above 2.52 V.

The timing is generated by charging and discharging the capacitor with a current of 2

µA between a threshold of

0.25 V and 1 V for 128 cycles. A 1-nF capacitor gives a delay time of 100 ms.

An RC filter connected at the VCC input is used to keep noise from the internal supply for the bandgap and other

analog circuitry. A typical value of 10R and 1

µF is used to filter the switching spikes, generated by the dc-dc

converters. A larger resistor than 10R should not be used because the current into VCC of up to 3 mA causes a

voltage drop at the resistor causing the undervoltage lockout circuitry connected at VCC internally to switch off

too early.

TPS65021 Datasheet(PDF) 39 Page - Texas Instruments