EP53F8QI Datasheet, PDF (9/12 Pages) Enpirion, Inc. – 1500 mA Synchronous Buck PWM DC-DC Converter with Integrated Inductor

EP53F8QI
Application Information
Setting the Output Voltage
V_IN
CIN
10uF
10Ω
680pF
1 uF
PVIN
POK
5.0pF
VOUT
EP53F8
AVIN1
AVIN2
ENABLE
VFB
AGND
PGND
Ra
237k
Rb
V_OUT
COUT
22 uF
Figure 5: Typical Application Circuit
The EP53F8QI uses a simple resistor divider to
program the output voltage.
Referring to Figure 5, use 237 kΩ, 1% or better
for the upper resistor (Ra). The value of the
bottom resistor (Rb) in kΩ is given as:
Rb  ^142.2 k
V_OUT  0.6
Where V_OUT is the output voltage. Rb should
also be a 1% or better resistor.
A 5.0pF MLCC capacitor is required in parallel
with Ra for compensation.
Power-Up/Down Sequencing
During power-up, ENABLE should not be
asserted before PVIN, and PVIN should not be
asserted before AVIN. The PVIN should never
be powered when AVIN is off. During power
down, the AVIN should not be powered down
before the PVIN. Tying PVIN and AVIN or all
three pins (AVIN, PVIN, ENABLE) together
during power up or power down meets these
requirements.
Pre-Bias Start-up
The EP53F8QI does not support startup into a
pre-biased condition. Be sure the output
capacitors are not charged or the output of the
EP53F8QI is not pre-biased when the
EP53F8QI is first enabled.
Input and Output Capacitor Selection
Low ESR MLC capacitors with X5R or X7R or
equivalent dielectric should be used for input
and output capacitors. Y5V or equivalent
dielectrics lose too much capacitance with
frequency, DC bias, and temperature.
Therefore, they are not suitable for switch-
mode DC-DC converter filtering, and must be
avoided.
The input filter capacitor requirement is a 10
µF, 10V 0805 MLCC capacitor in parallel with a
680pF MLCC capacitor. The 680pF capacitor
provides additional high frequency decoupling
and is manditory. The 680pF capacitor must
be placed closest to the EP53F8QI as shown
in Figure 5.
The output filter capacitor requirement is a
22 µF, 6.3V, 0805 MLCC for most applications.
The output ripple can be reduced by using 2 x
22 µF, 6.3V, 0805 MLC capacitors.
Additional bulk capacitance for decoupling and
bypass can be placed at the load as long as
there is sufficient separation between the V_OUT
Sense point and the bulk capacitance.
Excess total capacitance on the output (Output
Filter + Bulk) can cause an over-current
condition at startup. Refer to the section on
Soft-Start for the maximum total capacitance
on the output.
AVIN Decoupling
AVIN should be connected to PVIN using a
10Ω resistor. An 0402 or smaller case size is
recommended for this resistor. A 1 µF, 10 V,
0402 MLC capacitor should be connected from
AVIN to AGND to provide high frequency
decoupling for the control circuitry supply for
optimal performance.
POK Pull Up Resistor Selection
If the POK signal is required for the application.
The POK pin must be pulled up through a
resistor to any voltage source that can be as
high as V_IN. The simplest way is to connect
POK to the power input of the converter
through a resistor. A 100 kΩ pull up resistor is
recommended for most applications for
minimal current drain from the voltage source
and good noise immunity. POK can sink up to
5mA.
01542
October 11, 2013
www.altera.com/enpirion Page 9
Rev F