Rev 0.95 – March 2005
EN5310
Theory of Operation
Use an appropriate resistor ratio such that the desired
output voltage across the resistor pair causes the XFB
pin to be 0.8V at the nominal set-point. It is
Synchronous Buck Converter
The EN5310 is a synchronous, pin programmable
power supply with integrated power MOSFET
switches and inductor. The nominal input voltage
range is 2.5-5.0V. The output can be set to common
voltages by connecting appropriate combinations of 3
voltage selection pins to ground. If different voltage
levels are required, provision is also made to allow
external programming. The feedback control loop is
voltage-mode and the part uses a low-noise PWM
topology. Up to 1A of output current can be drawn
from this converter. The 5MHz operating frequency
enables the use of small-size output capacitors.
recommended that the resistor values used should be
in the 20K-40K range. Contact Enpirion Applications
Support for more specific information. If Over-
Voltage protection is required, the output of a second
divider to XOV should be set such that 0.96V is
present at the desired trip point. By design, if both
resistor dividers are the same, the OV trip-point will
be 20% above the nominal output voltage.
VIN
PVIN
AVIN
VOUT
VOUT
10µF
POK
SS
The power supply also has protection features such as:
• Programmable over-current protection (to
protect the IC from excessive load current)
• Thermal shutdown (to protect the converter
from getting too hot)
XOV
XFB
15 nF
22µF
AGND PGND
• Over-voltage protection that stops the PWM
switching and turns on the lower N-MOSFET
at 120% of the programmed output voltage in
order to protect the load from an OV
condition.
• Under-voltage lockout circuit to disable the
converter output when the input voltage is less
than approximately 2.2V
Table 1: Output Voltage Select Table
VS2*
VS1*
VS0* Output Voltage
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
3.3V
2.5V
1.8V
1.5V
1.25V
1.2V
Additional features include:
• Soft-start circuit, limiting the in-rush current
when the converter is powered up.
• Power good circuit indicating whether the
output voltage is within 90%-120% of the
programmed voltage.
0.8V**
User Selectable
** 0.8V ref only, not guaranteed performance
* The VS0, VS1 and VS2 pins are defaulted to a ‘1’
with an internal pull-up resistor. Only connect
these pins to AGND if a ‘0’ is required. If a ‘1’ is
required, then leave the pin floating.
Output Voltage Programming
The EN5310 output voltage is programmed using one
of two methods. Common output voltages are
achieved by tying one or more of the three Voltage
Select pins (VS0, VS1 & VS2) to ground (see Table
1). If all three are left floating, the output voltage and
over voltage thresholds are determined by the voltages
presented at the XFB and XOV pins respectively.
These voltages should be set by way of resistor
dividers between VOUT to GND with the midpoint
going to XFB and XOV.
Capacitor Selection
The EN5310 needs about 10-20uF of input
capacitance. Low-cost, low-ESR ceramic capacitors
can be used as input capacitors for this converter and
it is strongly recommended that they be rated X5R or
X7R. In some applications, lower value capacitors are
needed in parallel with the larger, lossy capacitors in
order to provide high frequency decoupling.
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ENPIRION [ ENPIRION, INC. ]
