XRP7714_1009 Datasheet, PDF (12/29 Pages) Exar Corporation – Quad Channel Digital PWM Step Down Controller

XRP7714
Quad Channel Digital PWM Step Down Controller
FUNCTIONAL DESCRIPTION AND OPERATION
The XRP7714 is a quad-output digital pulse width modulation (DPWM) controller with integrated
gate drivers for the use in synchronous buck switching regulators. Each output voltage can be
programmed from 0.9V to 5.1V without the need of an external voltage divider. The wide range of
the programmable DPWM switching frequency (from 300kHz to 1.5MHz) enables the user to
optimize for efficiency or component sizes. The digital regulation loop requires no external passive
components for network compensation. The loop performance does not need to be compromised
due to component tolerance, aging, and operating condition. Each digital controller provides a
number of safety features, such as over-current protection (OCP) and over-voltage protection
(OVP). The chip also provides over-temperature protection (OTP) and under-voltage lock-out
(UVLO) for two input voltage rails. The XRP7714 also has up to 6 GPIOs and a Standby Linear
Regulator to provide standby power. An I²C bus interface is provided to program the IC as well as
to communicate with the host for fault reporting and handling, power rail monitoring, channel
enable and disable, Standby LDO voltage reconfiguration, and Standby LDO enable and disable.
The XRP7714 offers a complete solution for soft-start and soft-stop. The delay and ramp of each
PWM regulator can be independently controlled. During soft-stop, the output voltage ramps down
with a programmable slope until it reaches a pre-set value. This pre-set value can be programmed
between within zero volts and the target voltage with the same set target voltage resolution.
REGISTER TYPES
There are two types of registers in the XRP7714: read/write registers and read-only registers. The
read/write registers are used for the control functions of the IC and can be programmed using
configuration non-volatile memory (NVM) or through an I²C command. The read-only registers are
for feedback functions such as error/warning flags and for reading the output voltage or current.
NON-VOLATILE CONFIGURATION MEMORY
The non-volatile memory (NVM) in XRP7714 stores the configuration data for the chip and all of the
power rails. This memory is normally configured during manufacturing time. Once a specific bit of
the NVM is programmed, that bit can never be reprogrammed again [i.e. one-time programmable].
During chip power up, the contents in the NVM are automatically transferred to the internal
registers of the chip. Programmed cells have been verified to be permanent for at least 10 years
and are highly reliable.
POWER UP AND SEQUENCING REQUIREMENTS
The XRP7714 can be programmed to sequence its outputs for nearly any imaginable loading
requirement. However, there are some important sequencing requirements for the XRP7714 itself.
When power is applied to the XRP7714, the 5V VCCA and 1.8V AVDD regulators must come up and
stabilize to provide power for the analog and digital blocks of the IC. The Enable Pin must remain
below its logic level high threshold until the AVDD is regulating to ensure proper loading of the
configuration registers. For systems that control the Enable signal through a microcontroller or
other processor, this is simply a matter of providing the proper delay to the Enable signal after
power up. However, most users will want the part to automatically power up when power is
applied to the system. To that end there are a number of recommended solutions.
The most ideal sequencing method is to provide an RC time constant delay from DVDD to the
Enable pin. A 10kohm resistor and a 0.1uF are all that is required. If the system needs to
externally control the Enable pin as well, it is recommended that the Enable pin be pulled to ground
using an open drain I/O. Using 3.3V active logic would back feed DVDD and exceed the maximum
rated voltage of the pin.
© 2010 Exar Corporation
12/29
Rev. 1.1.4