Datasheet
t =2
(reset)
x128x
(1V-0.25V)xC
(reset)
2 Am
()
TPS65020
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SLVS607C –SEPTEMBER 2005– REVISED SEPTEMBER 2011
VRTC Output
The VRTC output is typically connected to the Vcc_Batt pin of a Intel PXA270 processor. During power-up of the
processor, the TPS65020 internally switches from the LDO or the backup battery to the system voltage
connected at the VSYSIN pin (see Figure 25). It is required to add a capacitor of 4.7-μF minimum to the VRTC
pin, even the output may be unused.
LDO1 and LDO2
The LDOs default voltage is 1.1 V for LDO2 and 1.3 V for LDO1. They are intended to provide power to
VCC_PLL and the VCC_SRAM pin on a PXA270 processor. The minimum output capacitor required is 2.2 μF.
The LDOs output voltage is changed to different voltages between 1 V and 3.3 V using the I
2
C 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 providing the highest efficiency.
TRESPWRON
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.
While there is no real upper and lower limit for the capacitor connected to TRESPWRON, it is recommended to
not leave signal pins open.
(9)
Where:
t
(reset)
is the reset delay time
C
(reset)
is the capacitor connected to the TRESPWRON pin
The minimum and maximum values for the timing parameters called ICONST (2uA), TRESPWRON_UPTH (1V)
and TRESPWRON_LOWTH (0.25V) can be found under the electrical characteristics.
V
CC
-Filter
An RC filter connected at the VCC input is used to prevent noise from the internal supply for the bandgap and
other analog circuitry. A typical resistor value of 1 Ω and 1 μF is used to filter the switching spikes generated by
the dc-dc converters. A resistor larger than 10 Ω should not be used because the current (up to 3 mA) into VCC
causes a voltage drop at the resistor. This causes the undervoltage lockout circuitry connected internally at VCC
to switch off too early.
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