EN2340QI Datasheet, PDF (14/23 Pages) Enpirion, Inc. – 204A Voltage Mode Synchronous Buck PWM

Application Information
Output Voltage Programming and Loop
Compensation
The EN2340QI 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 11 shows the required
components and the equations to calculate their
values. The values recommended for C_A and R_CA
will vary with each PVIN and VOUT combination.
The EN2340 solution can be optimized for either
smallest size or highest performance. Please see
Table 6 for a list of recommended C_A and R_CA
values for each solution option.
The EN2340QI 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. Since VFB
is a sensitive node, do not touch the VFB node
while the device is in operation as doing so may
introduce parasitic capacitance into the control loop
that causes the device to behave abnormally and
damage may occur.
The EN2340QI 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 11). 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 6 for
compensation values for both options based on
input and output voltage conditions.
In some cases modifications to the compensation
may be required. The EN2340QI provides the
capability to modify the control loop response to
allow for customization for specific applications.
For more information, contact Altera MySupport
(www.altera.com/mysupport).
EN2340QI
VOUT
R_A
VFB
R_B
R_A =
C_A
180
VOUT
(R_A in kΩ)
Round R_A up to closest
R_CA ^{standard value higher than}
the calculated value.
R_B
=
V_FB × R_A
(V_OUT − V_FB )

V_FB is 0.75V
nominal

Figure 11: External Feedback
Compensation. See Table 6 for details.
Input Capacitor Selection
The EN2340QI requires a 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
rated. Y5V or e quivalent 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
De s cr iption
M FG
P/N
22µF, 16V,
X5R, 10%,
1206
Murata
GRM31CR61C226ME15
22µF, 16V,
X5R, 20%,
1206
Taiyo Yuden EMK316ABJ226ML-T
Table 3: Recommended Input Capacitors
Output Capacitor Selection
As seen from Table 6, the EN2340QI has been
optimized for use with either two 47µF/1206 or two
22µF/0805 output capacitors. Low ESR ceramic
capacitors are required with X5R or X7R rated
dielectric formulation. Y5V or e quivalent 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. In some
applications, extra bulk capacitance is required at
www.altera.com/enpirion, Page 14
06878
October 9, 2013
Rev E