SP6660 Datasheet, PDF (14/22 Pages) Sipex Corporation – 200mA Charge Pump Inverter or Doubler

FC
OSC
Oscillator
Frequency
open
open
10kHz typical
V+
open
80kHz typical
open or V+
external
capacitor
refer to Figure 11
open
external
clock
external clock
frequency
Figure 23. Four control modes for the SP6660
Oscillator Frequency
Oscillator Control
Refer to Figure 23 for a table of the four control
modes of the SP6660 internal oscillator
frequencies. In the first mode, FC and OSC are
open (unconnected) and the internal oscillator
typically runs at 10kHz. OSC is internally
connected to a 15pF capacitor.
In the second mode, FC is connected to V+. The
charge and discharge current at OSC changes
from 1.0µA to 8.0µA, increasing the oscillator
frequency eight times to 80kHz.
In the third mode, the oscillator frequency is
lowered by connecting a capacitor between OSC
and GND. FC can still multiply the frequency
by eight times in this mode, but for a lower range
of frequencies. Refer to Figure 11 for these ranges.
In the fourth mode, any standard CMOS logic
output can be used to drive OSC. OSC may be
overdriven by an external oscillator that swings
between V and GND. When OSC is overdriven,
IN
FC has no effect.
Unlike the 7660 and 660 industry standards,
designers may overdrive the oscillator of the
SP6660 in both the inverting and the Voltage
Doubling Mode.
Optimizing Loss Conditions
Losses in SP6660 applications can be anticipated
from the following:
1. Output Resistance:
V_LOSSΩ
=
I
LOAD
x
R
OUT
where V_LOSSΩ is the voltage drop due to the
SP6660 output resistance, I is the load
LOAD
current, and R is the SP6660 output resistance.
OUT
2. Charge Pump Capacitor ESR:
V_LOSSC1 ≈ 4 x ESR_C1 x I_LOAD
where V_LOSSC1 is the voltage drop due to the
charge pump capacitor, C1, ESR_C1 is the ESR of
C1, and I_LOAD is the load current. The loss in C1
is larger than the loss in the reservoir capacitor,
C2, because it handles a current almost four
times larger than the load current during charge-
pump operation. As a result of this, a change in
the capacitor ESR has a much greater impact on
the performance of the SP6660 for C1 than for C2.
3. Reservoir Capacitor ESR:
V_LOSSC2 = ESR_C2 x I_LOAD
where V_LOSSC2 is the voltage drop due to the
reservoir capacitor C2, ESR_C2 is the ESR of C2,
and I_LOAD is the load current. Increasing the
capacitance of C2 and/or reducing its ESR
can reduce the output ripple that may be
caused by the charge pump. A designer can
filter high-frequency noise at the output
by implementing a low ESR capacitor at C2.
Generally, capacitors with larger capacitance
values and higher voltage ratings tend to
reduce ESR.
SP6660DS/11
SP6660 200mA Charge Pump Inverter or Doubler
14
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