REG710_07 Datasheet, PDF (8/18 Pages) Burr-Brown (TI) – 60mA Switched-Cap BUCK/BOOST CONVERTER

REG710
SBAS221E − DECEMBER 2001 − REVISED SEPTEMBER 2003
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 Resist-
ance (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 and 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.
C_PUMP
0.22µF
Enable ₃ ⁴
6
V_IN
5
1
C_IN
2.2µF
REG710
2 GND
V_OUT
C_OUT
2.2µF
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The approximate efficiency is given by:
Efficiency (%) = V_OUT/(2 × V_IN) × 100
(step-up operating mode)
or
V_OUT
V_IN
100
(step-down operating mode)
Table 2 lists the approximate values of the input voltage at
which the device changes internal operating mode.
See efficiency curves in the Typical Characteristics section
for various loads and input voltages.
Table 2. Operating Mode Change Versus V_IN
PRODUCT
REG710-2.5
REG710-2.7
REG710-3
REG710-3.3
REG710-5, REG71050, REG71055
OPERATING MODE
CHANGES AT VIN OF
> 3.2V
> 3.4V
> 3.7V
> 4.0V
Step-Up Only
Figure 3. Typical Operating Circuit
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 1 can be used with the
REG710. This is only a representative list of those parts
that are compatible.
LAYOUT
Large transient currents flow in the V_IN, V_OUT, and GND
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.
AREA: < 0.08 sq. inches ^VENABLE
V_IN
V_OUT
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.
C_OUT
C_P
C_IN
GND
Figure 4. Suggested PCB Design for Minimum Ripple
Table 1. Suggested Capacitors
MANUFACTURER
PART NUMBER
Kemet
Panasonic
Taiyo Yuden
C1206C255K8RAC
C1206C224K8RAC
ECJ−2YBOJ225K
ECJ−2VBIC224K
ECJ−2VBIC104
EMK316BJ225KL
TKM316BJ224KF
VALUE
2.2µF
0.22µF
2.2µF
0.22µF
0.1µF
2.2µF
0.22µF
TOLERANCE
±10%
±10%
±10%
±10%
±10%
±10%
±10%
DIELECTRIC
MATERIAL
X7R
X7R
X5R
X7R
X7R
X7R
X7R
PACKAGE
SIZE
1206
1206
805
805
805
1206
1206
RATED
WORKING
VOLTAGE
10V
10V
6.3V
16V
16V
16V
25V
8