XRP7708 Datasheet, PDF (12/27 Pages) Exar Corporation – Quad Channel Digital PWM Step Down Controller

XRP7708
Quad Channel Digital PWM Step Down Controller
FUNCTIONAL DESCRIPTION AND OPERATION
The XRP7708 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 300 kHz to 1.5 MHz) 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 XRP7708 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 Low Drop-out Regulator voltage reconfiguration, and Standby LDO
enable and disable.
The XRP7708 offers a complete solution for soft-start and soft-stop. The delay and ramp of each
PWM regulator can be independently controlled. When a pre-bias voltage is present, the device
holds both high-side and low-side MOSFETs off until the reference voltage ramps up higher than
the output voltage. As a result, large negative inductor current and output voltage disturbance are
avoided. During soft-stop, the output voltage ramps down with a programmable slope until it
reaches a pre-set stop voltage. This pre-set value can be programmed between within zero volts
and the target voltage with the same set target voltage resolution (see shutdown waveforms in
Applications).
REGISTER TYPES
There are two types of registers in the XRP7708: 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 XRP7708 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.
CHIP POWER-UP
The figure below shows the power-up sequence of XRP7708 during the normal operation. The
startup stage is divided into three phases. The first phase is the internal LDO power-up phase. The
second phase is the configuration transfer phase. The third phase is chip ready phase. The power
up sequence is less than 1ms.
© 2010 Exar Corporation
12/27
Rev. 1.0.3