SP6681 Datasheet, PDF (7/10 Pages) Sipex Corporation – High Efficiency Boost Charge Pump Regulator

+3.6V
Lithium-Ion
Battery
4.7µF
2.2µF
2.2µF
CF1P
2
V_{IN 3}
C/4
Cx8
CLK
CF1N
9
CF2P
10
CF2N
7
SP6681
V_OUT
1
4 56
8
GND
5.0V output
2.2µF
Figure 3. Typical SIM Card Application Circuit for the SP6681
Any standard CMOS logic output is suitable for
driving the C/4 or Cx8 control lines as long as
logic low is less than 0.4V and logic high is
greater than 1.3V.
CLK pin
not present
C/4 pin
X
Cx8 pin
X
f_PUMP
0
32.768kHz
low
low 32.768kHz
32.768kHz
low
high 262.14kHz
32.768kHz
high
low
8.192kHz
32.768kHz
high
high 262.14kHz
Table 1. Control Line Logic for the Internal Charge
Pump Oscillator
Efficiency
Power efficiency with the SP6681 charge pump
regulator is improved over standard charge pumps
doubler circuits by the inclusion of an 1.5X
output mode, as described in the Theory of
Operation section. The net result is an increase
in efficiency at battery inputs greater than 3.7 to
3.8V where the SP6681 switches to the 1.5X
mode.
Capacitor Selection
In order to maintain the lowest output resistance,
input ripple voltage and output ripple voltage,
multi-layer ceramic capacitors with inherently
low ESR are recommended. Refer to Table 2 for
some suggested low ESR capacitors. Tables of
output resistance and ripple voltages for a vari-
ety of input, output and pump capacitors are
included here to use as a guide in capacitor
selection. Measured conditions are with CLK =
32kHz, 5mA output load and all capacitors are
2.2uF except when stated otherwise. A DC
power supply with added 0.25ohm output ESR
was used to simulate a Lithium Ion Battery as
shown in figure 4.
Board Layout
PC board layout is an important design consider-
ation to mitigate switching current effects. High
frequency operation makes PC layout important
for minimizing ground bounc and noise. Com-
ponents should be place as close to the IC as
possible with connections made through short,
low impedance traces. To maximize output
ripple voltage, use a ground plane and solder the
IC's GND pin directly to the ground plane.
+
Power Supply
HP3631A
1000µF
-
0.25ohm
0.75” Leads ^{VIN (p-p)}
SP6681 EvBd
2.2µF Caps ^{VOUT (p-p)}
Figure 4. Capacitor Selection Test Circuit
Rev:A Date: 11/20/03
SP6681 High Efficiency Boost Charge Pump Regulator
7
© Copyright 2002 Sipex Corporation