SP3220EBEA-L-TR Datasheet, PDF (12/20 Pages) Exar Corporation – 3.0V to +5.5V RS-232 Driver/Receiver Pair

Charge Pump Design Guidelines
The charge pump operates with 0.1µF ca-
pacitors for 3.3V operation. For other supply
voltages, see the table for required capacitor
values. Do not use values smaller than those
listed. Increasing the capacitor values (e.g.,
by doubling in value) reduces ripple on the
transmitter outputs and may slightly reduce
power consumption. C2, C3, and C4 may be
increased without changing C1’s value.
Minimum recommended charge pump
capacitor value
Input Voltage
Vcc
Charge pump
capacitor value for
SP3220E/EB/EU
3.0V to 3.6V
C1 - C4 = 0.1µF
3.0V to 5.5V
C1 - C4 = 0.22µF
The charge pump oscillator typically operates
at greater than 250kHz allowing the pump to
run efficiently with small 0.1μF capacitors.
Efficient operation depends on rapidly charg-
ing and discharging C1 and C2, therefore
capacitors should be mounted close to the
IC and have low ESR (equivalent series
resistance).
Low cost surface mount ceramic capacitors
(such as are widely used for power-supply
decoupling) are ideal for use on the charge
pump. However the charge pumps are de-
signed to be able to function properly with a
wide range of capacitor styles and values.
If polarized capacitors are used the positive
and negative terminals should be connected
as shown in the Typical Operating Circuit.
DESCRIPTION
Voltage potential across any of the capaci-
tors will never exceed 2 x VCC. Therefore
capacitors with working voltages as low as
6.3V rating may be used with a 3.0V VCC
supply. The reference terminal of the V+
capacitor may be connected either to VCC
or ground, but if connected to ground a
minimum 10V working voltage is required.
Higher working voltages and/or capacitance
values may be advised if operating at higher
VCC or to provide greater stability as the
capacitors age.
Under lightly loaded conditions the intelligent
pump oscillator maximizes efficiency by
running only as needed to maintain V+ and
V-. Since interface transceivers often spend
much of their time at idle this power-efficient
innovation can greatly reduce total power
consumption. This improvement is made
possible by the independent phase sequence
of the Exar charge-pump design.
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
12
SP3220E_EB_EU_102_102016