AAT3111 Datasheet, PDF (12/16 Pages) Advanced Analogic Technologies – MicroPower™ Regulated Charge Pump

AAT3111
MicroPower™ Regulated Charge Pump
Applications Information
and low frequency components of the charge pump
output ripple response. If a higher value tantalum
capacitor is used for C_OUT to reduce low frequency
ripple elements, a small 1µF low ESR ceramic
capacitor should be added in parallel to the tantalum
capacitor (see Figure 1). The reason for this is tan-
talum capacitors typically have higher ESR than
equivalent value ceramic capacitors and are less
able to reduce high frequency components of the
output ripple. The only disadvantage to using large
values for the C_OUT capacitor is the AAT3111 device
turn-on time and in-rush current may be increased.
If additional ripple reduction is desired, an R/C filter
can be added to the charge pump output in addi-
tion to the C_OUT capacitor (see Figure 2). An R/C
filter will reduce output ripple by primarily attenuat-
ing high frequency components of the output ripple
waveform. The low frequency break point for the
R/C filter will significantly depend on the capacitor
value selected.
Layout Considerations
High charge pump switching frequencies and large
peak transient currents mandate careful printed cir-
cuit board layout. As a general rule for charge
pump boost converters, all external capacitors
should be located as close as possible to the
device package with minimum length trace con-
nections. Maximize the ground plane around the
AAT3111 charge pump and make sure all external
capacitors are connected to the immediate ground
plane. A local component side ground plane is rec-
ommended. If this is not possible due the layout
design limitations, assure good ground connec-
tions by the use of large or multiple pcb via's.
Refer to the following AAT3111 evaluation board for
an example of good charge pump layout design
(Figures 3 through 5).
VOUT
(3.3V)
COUT2
1µF
COUT1
+
22µF
V_OUT
C+
AAT3111
GND
VIN
ON/OFF
SHDN C-
Figure 1: Application using tantalum capacitor
VOUT
(3.3V)
CFILTER
33µF
RFILTER
1.5 ohms
COUT
10µF
V_OUT
C+
AAT3111
GND
VIN
ON/OFF
SHDN C-
Figure 2: Application with output ripple reduction filter
CFLY
1µF
+ _CIN
10µF
VIN
(1.8V to 3.3V)
CFLY
1µF
VIN
CIN ^{(1.8V to 3.3V)}
10µF
12
3111.2002.3.0.91