XR77128 Datasheet, PDF (13/28 Pages) Exar Corporation – Quad Output Digital PWM/PFM

XR77128
Functional Description
Overview
The XR77128 is a quad-output digital pulse width modula-
tion (PWM) controller with integrated gate drivers for use
with synchronous buck switching regulators. Each output
voltage can be programmed from 0.6V to 5.5V without the
need for an external voltage divider. The wide range of pro-
grammable PWM switching frequency (from 105 kHz to 1.2
MHz) enables the user to optimize for efficiency or compo-
nent sizes. Since the digital regulation loop requires no
external passive components, loop performance is not
compromised due to external component variation or oper-
ating condition.
The XR77128 provides a number of critical safety features
such as Over-Current Protection (OCP), Over-Voltage Pro-
tection (OVP), Over-Temperature Protection (OTP), plus
input Under-Voltage Lockout (UVLO). In addition, it has a
number of key health monitoring features such as warning
level flags for the safety functions, Power Good (PGOOD),
etc., plus full monitoring of system voltages and currents.
The above are all programmable and/or readable from the
SMBus and many are steerable to the IOs for hardware
monitoring.
For hardware communication, the XR77128 has two logic
level General Purpose Input-Output (GPIO) pins and three
15V, open drain, Power System Input-Output (PSIO) pins.
Two pins are dedicated to the SMBus data (SDA) and clock
(SCL). Additional pins include Chip Enable (Enable), Aux
Boost Feedback (BFB) and External PLL Capacitor (CPLL).
In addition to providing four switching outputs, the XR77128
also provides control for an Aux boost supply, and two
stand-by linear regulators for a total of seven customer
usable supplies in a single device.
The 5V LDO is used for internal power and is also available
for customer use to power external circuitry. LDOOUT is
solely for customer use and is not used by the chip. There
is also a 1.8V linear regulator which is for internal use only
and should not be used externally.
A key feature of the XR77128 is its advanced power man-
agement capabilities. All four outputs are independently
programmable and provide the user full control of the delay,
ramp, and sequence during power up and power down. The
user may also control how the outputs interact and power
down in the event of a fault. This includes active ramp down
of the output voltages to remove an output voltage as
quickly as possible. Another useful feature is that the out-
puts can be defined and controlled as groups.
The XR77128 has two main types of programmable mem-
ory. The first type is runtime registers that contain configu-
ration, control and monitoring information for the chip. The
second type is rewritable Non-Volatile Flash Memory that is
used for permanent storage of the configuration data along
with various chip internal functions. During power up, the
run time registers are loaded from the flash memory allow-
ing for standalone operation.
The XR77128 brings an extremely high level of functionality
and performance to a programmable power system. Ever
decreasing product budgets require the designer to quickly
make good cost/performance tradeoffs to be truly success-
ful. By incorporating 4 switching channels, two user LDOs,
a charge pump boost controller, along with internal gate
drivers, all in a single package, the XR77128 allows for
extremely cost effective power system designs. Another key
cost factor that is often overlooked is the unanticipated
Engineering Change Order (ECO). The programmable ver-
satility of the XR77128, along with the lack of hard wired
configuration components, allows for minor and major
changes to be made in circuit by simple reprogramming.
© 2014 Exar Corporation
13 / 28
exar.com/XR77128
Rev 1A