XRP7720 Datasheet, PDF (16/28 Pages) Exar Corporation – Quad Output Universal Customizable PMIC with PFM

XRP7720
Quad Output Universal Customizable PMIC with PFM
voltage in regulation while maintaining the
30kHz switching frequency.
Under extremely light or zero load currents,
the GH on time pulse width can decrease to its
minimum width. When this happens, the lower
FET on time is increased slightly to allow a
small amount of reverse inductor to flow back
into Vin to keep the output voltage in
regulation while maintaining the switching
frequency above the audio range.
INTERNAL DRIVERS
The internal high and low gate drivers use
totem pole FETs for high drive capability. They
are powered by two external 5V power pins
(VCCD1-2) and (VCCD3-4), VCCD1-2 powers
the drivers for channels 1 and 2 and VCCD3-4
powers channels 3 and 4. The drivers can be
powered by the internal 5V LDO by connecting
their power pins to the LDO5 output through
an RC filter to avoid conducted noise back into
the analog circuitry.
To minimize power dissipation in the 5V LDO,
it is recommended to power the drivers from
an external 5V power source either directly or
by using the V5EXT input. Good quality 1uF to
4.7uF capacitors should be connected directly
between the power pins to ground to optimize
driver performance and minimize noise
coupling to the 5V LDO supply.
The driver outputs should be connected
directly to their corresponding output
switching FETs, with the Lx output connected
to the drain of the lower FET for the best
current monitoring accuracy.
See ANP-32 “Practical Layout Guidelines for
Power^XR Designs”
LDOS
The XRP7720 has an internal Low Drop Out
(LDO) linear regulator that generates 5.0V
(LDO5) for both internal and external use.
Additionally it has a 1.8V regulator that
supplies power for the XRP7720 internal
circuits. Figure 3 shows a block diagram of the
linear power supplies. LDO5 is the main power
input to the device and is supplied by an
external 5.5V to 18V (VCC) supply. The output
of LDO5 should be bypassed by a good quality
capacitor connected between the pin and
ground close to the device. The 5V output is
used by the XRP7720 as a standby power
supply and is also used to power the 3.3V and
1.8V linear regulators inside the chip and can
also supply power to the 5V gate drivers. The
total output current that the 5V LDO can
provide is 100mA. The XRP7720 consumes
approximately 20mA and the rest can be used
by the gate drive currents. During initial
power up, the maximum external load should
be limited to 30mA.
The AVDD pin is the 1.8V regulator output and
needs to be connected externally to the DVDD
pin on the device. A good quality capacitor
should be connected between this pin and
ground close to the package.
For operation with a VCC of 4.75V to 5.5V, the
LDO5 output needs to be connected directly to
VCC on the board.
© 2014 Exar Corporation
16/28
Rev. 1.0.0