XRP6670 Datasheet, PDF (7/13 Pages) Exar Corporation – 3A 300kHz-2.5MHz Synchronous Step Down Regulator

XRP6670
3A 300kHz-2.5MHz Synchronous Step Down Regulator
THEORY OF OPERATION
FUNCTIONAL DESCRIPTION
The XRP6670 is a synchronous, current-mode,
step-down regulator. It regulates input
voltages from 2.6V to 5.5V and supplies up to
3A of output current I_OUT. The XRP6670 uses
current-mode control to regulate the output
voltage V_OUT. The V_OUT is measured at FB
through a resistive voltage divider and input to
a transconductance error amplifier. The high-
side switch current is compared to the output
of the error amplifier to control the output
voltage. The regulator utilizes internal P-
channel and N-channel MOSFETs to step-down
the input voltage. Because the high-side FET is
P-channel a bootstrapping capacitor is not
necessary and the regulator can operate at
100% duty cycle. The XRP6670 has several
powerful protection features including OCP,
OTP, UVLO and output short-circuit.
SHORT-CIRCUIT AND OVER-CURRENT
PROTECTION OCP
The XRP6670 protects itself and downstream
circuits against accidental increase in current
or short-circuit. If peak current through the
switching FET increases above 4.2A (nominal)
the regulator enters an idle state where the
internal FETs are turned off and softstart is
pulled low. After a period of 2000xT the
regulator will attempt a softstart. If the high
current persists the protection cycle will
repeat.
SOFT-START
XRP6670 has an integrated soft-start which is
preset at 1.5ms (nominal). This feature limits
the inrush current during startup and allows
the output voltage to smoothly rise to its
programmed value.
POWER GOOD FLAG
This open drain output (PGOOD) can be used
to monitor whether the output voltage is
within regulation (±15%). PGOOD is pulled to
ground when V_OUT is not in regulation. PGOOD
should be tied to VDD with a 100k resistor.
PROGRAMMABLE FREQUENCY
The switching frequency is programmable
within a range of 300kHz to 2.5MHz via a
resistor placed between SHDN/RT and GND
pins. An equation for calculating a resistor
value for a target frequency is given the
Application Information section.
100% DUTY CYCLE AND LDO OPERATION
The XRP6670 switching FET is a P-channel
device and therefore can operate at 100%
duty cycle. In battery operated applications
where V_IN will droop, XRP6670 can seamlessly
transition from PWM to LDO mode.
OVER-TEMPERATURE PROTECTION OTP
If the junction temperature exceeds 160°C the
OTP circuit is triggered, turning off the internal
control circuit and FETs. When junction
temperature drops below 140°C the XRP6670
will restart.
Although thermal shutdown is built-in in the
XRP6670 to protect the device from thermal
damage, the total power dissipation that the
XRP6670 can sustain is based on the package
thermal capability. Equation 1 shown on page
two, can be used to calculate junction
temperature and ensure operation within the
recommended maximum temperature of
125°C.
APPLICATION INFORMATION
PROGRAMMING THE OUTPUT VOLTAGE
Use an external resistor divider to set the
output voltage based on the following
equation:
1
2
0.800 ¹
Where:
R1 is the resistor between V_OUT and FB
(nominally set at 100kΩ)
© 2013 Exar Corporation
7/13
Rev. 1.0.1