LTC1046 Linear Technology, LTC1046 Datasheet - Page 5

• Manufacturer Part Number: LTC1046
• Description: Inductorless 5V to + 5V Converter
• Manufacturer: Linear Technology

Rewriting in terms of voltage and impedance equivalence,
A new variable, R
R
capacitor network is as shown in Figure 3.
Examination of Figure 4 shows that the LTC1046 has the
same switching action as the basic switched capacitor
building block. With the addition of finite switch ON
resistance and output voltage ripple, the simple theory,
although not exact, provides an intuitive feel for how the
device works.
For example, if you examine power conversion efficiency
as a function of frequency (see typical curve), this simple
theory will explain how the LTC1046 behaves. The loss,
and hence the efficiency, is set by the output impedance.
A
BOOST
EQUIV
OSC
(1)
(7)
3x
PPLICATI
I
= 1/fC1. Thus, the equivalent circuit for the switched
Figure 3. Switched Capacitor Equivalent Circuit
V
OSC
1
(6)
LV
1
/
–
Figure 4. LTC1046 Switched Capacitor
Voltage Converter Block Diagram
fC
V
1
2
R
O
V1
EQUIV
(8)
V
+2
CLOSED WHEN
+
V
R
EQUIV
U
V
1
=
EQUIV
R
+
EQUIV
> 3.0V
–
S
fC1
1
V
, has been defined such that
2
I FOR ATIO
U
.
SW1
C2
R
CAP +
CAP –
+
1046 F03
GND
W
L
(2)
(4)
(3)
V2
C1
SW2
1046 F04
U
V
(5)
OUT
+
C2
As frequency is decreased, the output impedance will
eventually be dominated by the 1/fC1 term and power
efficiency will drop. The typical curves for power effi-
ciency versus frequency show this effect for various capaci-
tor values.
Note also that power efficiency decreases as frequency
goes up. This is caused by internal switching losses which
occur due to some finite charge being lost on each
switching cycle. This charge loss per unit cycle, when
multiplied by the switching frequency, becomes a current
loss. At high frequency this loss becomes significant and
the power efficiency starts to decrease.
LV (Pin 6)
The internal logic of the LTC1046 runs between V
(Pin 6). For V
switch shorts LV to GND (Pin 3). For V
LV pin should be tied to ground. For V
equal to 3V, the LV pin can be tied to ground or left floating.
OSC (Pin 7) and BOOST (Pin 1)
The switching frequency can be raised, lowered or driven
from an external source. Figure 5 shows a functional
diagram of the oscillator circuit.
BOOST
(1)
(6)
LV
+
greater than or equal to 3V, an internal
2I
2I
Figure 5. Oscillator
V
+
I
I
1046 F05
14pF
OSC
(7)
+
+
less than 3V, the
greater than or
LTC1046
SCHMITT
TRIGGER
+
and LV
5