SP6832 Datasheet, PDF (8/15 Pages) Sipex Corporation – High Speed, High Efficiency Voltage Inverter

DESCRIPTION
The SP6832 is a CMOS Charge Pump Voltage
Converter that can be used to invert a +1.15V
to +5.3V input voltage. These devices are ideal
for designs involving battery-powered and/or
board level voltage conversion applications.
The typical operating frequency of the SP6832
is 500kHz. The SP6832 has a typical operating
current of 800µA. The device can output 25mA
with a voltage drop of 500mV. The devices are
ideal for designs using +3.3V or +3.6V lithium
ion batteries such as cell phones, PDAs, medical
instruments, and other portable equipment.
The SP6832 combines a high efficiency with
a low quiescent current.
THEORY OF OPERATION
The SP6832 should theoretically produce an
inverted input voltage. In real world applications,
there are small voltage drops at the output that
reduce efficiency. The circuit of an ideal voltage
inverter can be found in Figure 16. The voltage
inverters require two external capacitors to
store the charge. A description of the two
phases follows:
Phase 1
In the first phase of the clock cycle, switches S1
and S3 are opened and S2 and S4 are closed.
This connects the flying capacitor, C1, from V_IN
to ground. C1 charges up to the input voltage
applied at V .
IN
Phase 2
In the second phase of the clock cycle, switches
S1 and S3 are opened and S2 and S4 are closed.
This connects the flying capacitor, C1, in parallel
with the output capacitor, C2. The charge stored
in C1 is now transferred to C2. Simultaneously,
the negative side of C2 is connected to V_OUT and
the positive side is connected to ground. With
the voltage across C2 smaller than the voltage
across C1, the charge flows from C1 to C2 until
the voltage at the V equals -V .
OUT
IN
V_OUT = -VIN
V_IN
S1
S2
C1
C2
S3
S4
V_OUT
Figure 16. Circuit for an Ideal Voltage Inverter
Charge-Pump Output
The output of the SP6832 is not regulated and
therefore is dependent on the output resistance
and the amount of load current. As the load
current increases, losses may slightly increase
at the output and the voltage may become
slightly more positive. The loss at the negative
output, V_LOSS, equals the current draw, I_OUT, from
V times the negative converter's source
OUT
resistance, R_S:
V =I xR.
LOSS OUT
S
The actual inverted output voltage at V will
OUT
equal the inverted voltage difference of V_IN and
V_LOSS:
V_OUT = -(V_IN - V_LOSS).
Efficiency
Theoretically, the total power loss of a switched
capacitor voltage converter can be summed up as
follows:
∑P_LOSS
=
P
INT
+
P
CAP
+
P,
CONV
where P_LOSS is the total power loss, P_INT is the total
internal loss in the IC including any losses in the
MOSFET switches, P is the resistive loss of
CAP
SP6832DS/04
SP6832 High Speed, High Efficiency Voltage Inverter
8
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