EN2390QI Datasheet, PDF (13/21 Pages) Enpirion, Inc. – 9A Voltage Mode Synchronous Buck PWM

Application Information
Output Voltage Programming and Loop
Compensation
The EN2390QI output voltage is programmed using
a simple resistor divider network. A phase lead
capacitor (C_A) plus a resistor (R_CA) are required for
stabilizing the loop. Figure 6 shows the required
components and the equations to calculate their
The EN2390QI output voltage is determined by the
voltage presented at the VFB pin. This voltage is
set by way of a resistor divider between VOUT and
AGND with the midpoint going to VFB.
The EN2390QI uses a Type IV compensation
network. Most of this network is integrated.
However a phase lead capacitor and a resistor are
required in parallel with the upper resistor of the
external feedback network (see Figure 6). Total
compensation is optimized for either low output
ripple or small solution size, and will result in a wide
loop bandwidth and excellent load transient
performance for most applications. See Table 5 for
compensation values for both options based on
input and output voltage conditions.
In some cases modifications to the compensation
may be required. The EN2390QI provides the
capability to modify the control loop response to
allow for customization for specific applications.
For more information, contact Enpirion Applications
Engineering support ([e-mail]).
Figure 6: V_OUT Resistor Divider & Compensation
Components. RA equation is only valid
for Best Performance option. For Small
Solution Size option, see Table 5.
Input Capacitor Selection
The EN2390QI requires two 22µF/1206 input
capacitor. Low-cost, low-ESR ceramic capacitors
should be used as input capacitors for this
converter. The dielectric must be X5R or X7R
EN2390QI
values. The values recommended for C_A and R_CA
will vary with each PVIN and VOUT combination.
The EN2390 solution can be optimized for either
smallest size or highest performance. Please see
Table 5 for a list of recommended C_A and R_CA
values for each solution option.
rated. Y5V or equivalent dielectric formulations
must not be used as these lose too much
capacitance with frequency, temperature and
bias voltage. In some applications, lower value
capacitors are needed in parallel with the larger,
capacitors in order to provide high frequency
decoupling. Table 3 contains a list of
recommended input capacitors.
Recommended Input Capacitors
Description
22µF, 16V, X5R,
10%, 1206
22µF, 16V, X5R,
20%, 1206
MFG
Murata
Taiyo
Yuden
P/N
GRM31CR61C226ME15
EMK316ABJ226ML-T
Table 3: Recommended Input Capacitors
Output Capacitor Selection
As seen from Table 5, the EN2390QI has been
optimized for use with two 47µF/0805 and two
22µF/0805 output capacitors for best performance.
For smallest solution size, various combinations of
output capacitance may be used. See Table 5 for
details. Low ESR ceramic capacitors are required
with X5R or X7R rated dielectric formulation. Y5V
or equivalent dielectric formulations must not
be used as these lose too much capacitance
with frequency, temperature and bias voltage.
Table 4 contains a list of recommended output
capacitors
Output ripple voltage is determined by the
aggregate output capacitor impedance. Capacitor
impedance, denoted as Z, is comprised of
capacitive reactance, effective series resistance,
ESR, and effective series inductance, ESL
reactance.
Placing output capacitors in parallel reduces the
impedance and will hence result in lower ripple
voltage.
1 11
1
= + + ... +
Z
ZZ
Z
Total
1
2
n
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