AIC1845 ETC2 [List of Unclassifed Manufacturers], AIC1845 Datasheet - Page 9

• Manufacturer Part Number: AIC1845
• Description: Regulated 5V Charge Pump In SOT-23
• Manufacturer: ETC2 [List of Unclassifed Manufacturers]

For AIC1845, the controller takes the PSM (Pulse
Skipping Modulation) control strategy. When the
duty cycle is limited to 0.5, there will be:
According to the equation (4), we know that as
long as the flying capacitor C1 is at steady state,
the input current is twice the output current. The
efficiency of charge pump is given below:
V
Fig. 21 The off state of charge pump circuit
Fig. 20 The on state of charge pump circuit
C
C
V
IN
IN
IN
IN
I
I
I
I
I
I
I
η
ON
IN
IN
ON
OUT
ON
ON
ION
-
−
=
=
-
-
=
AVE
AVE
AVE
=
=
AVE
I
2I
=
ON
V
2
2
R
I
OUT
OUT
R
×
×
×
V
OFF
×
DS-ON
-
=
×
AVE
IN
DS-ON
I
D
I
I
0.5
OFF
ON
OFF
I
Q1
DT
Q3
OFF
-
×
×
=
AVE
Q3
-
×
I
I
AVE
-
×
I
OUT
IN
AVE
-
=
OFF
D
AVE
T
Q1
×
I
+
OFF
R
×
=
-
(1
×
AVE
I
=
DS-ON
D
ESR
OFF
I
C1
ESR
(1
−
OFF
−
C1
V
AVE
V
R
D
-
×
-
OUT
IN
AVE
D)
-
DS-ON
)
(1
AVE
Q4
×
×
−
×
2I
×
(1
Q4
D)
×
I
(1
OUT
OUT
Q2
−
1 (
Q2
−
D)T
−
D)
0.5)
=
C
V
V
C
2V
V
OUT
OUT
OUT
×
OUT
OUT
IN
T
(1)
(2)
(3)
External Capacitor Selection
Three external capacitors, C
determine AIC1845 performances, in the aspects
of output ripple voltage, charge pump strength
and transient. Optimum performance can be
obtained by the use of ceramic capacitors with
low ESR. Due to high ESR, capacitors of tantalum
and aluminum are not recommended for charge
pump application.
To reduce noise and ripple, a low ESR ceramic
capacitor, ranging from 2.2µF to 10µF, is
recommended for C
C
voltage. An output capacitor with larger value
results in smaller ripple.
C
The larger C
smaller ripple voltage obtain. However, large C
and C
The ratio of C
be approximately 10:1.
The value of capacitors, which is used under
operation conditioin, determines the performance
of a charge pump converter. And two factors, as
follows, affect the capacitance of capacitor.
1. Material: Ceramic capacitors of different
OUT
FLY
materials, such as X7R, X5R, Z5U and Y5V,
have different tolerance in temperature and
differnet cpacitance loss. For example, a X7R
or X5R type of capacitor can retain most of
the capacitance at temperature from -40°C to
85°C, but a Z5U or Y5V type will lose most of
the capacitance at that temperature range.
is critical for the strength of charge pump.
determines the amount of output ripple
OUT
are expected when a large C
FLY
IN
(as well as C
is, the larger output current and
IN
and C
OUT
IN
OUT
, C
) to C
AIC1845
. The value of
OUT
..........(5)
....
FLY
....
FLY
and C
..(6)
applies.
should
FLY
9
IN
,