Datasheet

REG711
8
SBVS027A
CAPACITOR SELECTION
For minimum output voltage ripple, the output capacitor
C
OUT
should be a ceramic, surface-mount type. Tantalum
capacitors generally have a higher Effective Series Resis-
tance (ESR) and may contribute to higher output voltage
ripple. Leaded capacitors also increase ripple due to the
higher inductance of the package itself. To achieve best
operation with low input voltage and high load current, the
input and pump capacitors (C
IN
, C
PUMP
respectively) should
also be surface-mount ceramic types. In all cases, X7R or
X5R dielectric are recommended. See the Typical Operating
Circuit shown in Figure 3 for component values.
The approximate efficiency is given by:
Efficiency (%) = V
OUT
/(2 • V
IN
) •100 (step-up operating mode)
or
V
OUT
• 100/V
IN
(step-down operating mode)
Table II lists the approximate values of the input voltage at
which the device changes internal operating mode.
OPERATING MODE
PRODUCT CHANGES AT V
IN
OF
REG711-2.5 > 3.2V
REG711-2.7 > 3.4V
REG711-3.0 > 3.7V
REG711-3.3 > 4.0V
REG711-5.0 Step-up only
TABLE II.
See efficiency curves in the Typical Performance Curves
section for various loads and input voltages.
LAYOUT
Large ripple currents flow in the V
IN
, PGND and V
OUT
traces. To minimize both input and output ripple, keep the
capacitors as close as possible to the regulator using short,
direct circuit traces.
A suggested PCB routing is shown in Figure 4. The trace
lengths from the input and output capacitors have been kept
as short as possible. A star ground system has been imple-
mented, with pin 5 as the center of the star. No ground plane
is provided in other layers, as this will provide capacitive
coupling for noise spikes.
FIGURE 4. Suggested PCB Design for Minimum Ripple.
With light loads or higher input voltage, a smaller 0.1µF
pump capacitor (C
PUMP
) and smaller 1µF input and output
capacitors (C
IN
and C
OUT
, respectively) can be used. To
minimize output voltage ripple, increase the output capaci-
tor, C
OUT
, to 10µF or larger.
The capacitors listed in Table I have been used with the
REG711. This is only a representative list of those parts that
are compatible, and not the results of a complete survey of
an industry-wide offering.
EFFICIENCY
The efficiency of the charge pump regulator varies with the
output voltage version, the applied input voltage, the load
current, and the internal operation mode of the device.
FIGURE 3. Typical Operating Circuit.
C
PUMP
0.22µF
V
IN
V
OUT
C
IN
2.2µF
PGND
ENABLE
GND
2
76
8
54
3
C
OUT
2.2µF
REG711
NOTE: All Capacitors 1206 Size
RATED
DIELECTRIC PACKAGE WORKING
MANUFACTURER PART NUMBER VALUE TOLERANCE MATERIAL SIZE VOLTAGE
Kemet C1206C255K8RAC 2.2µF ±10% X7R 1206 10V
C1206C224K8RAC 0.22µF ±10% X7R 1206 10V
Panasonic ECJ3YB1A225K 2.2µF ±10% X7R 1206 10V
ECJ3VB1C224K 0.22µF ±10% X7R 1206 16V
Taiyo Yuden LMK325BJ106KN 10µF ±10% X5R 1210 10V
EMK316BJ225KL 2.2µF ±10% X7R 1206 16V
TKM316BJ224KF 0.22µF ±10% X7R 1206 25V
TABLE I. Capacitors That Have Been Successfully Used With The REG711.