AIC1845 Datasheet, PDF (10/13 Pages) List of Unclassifed Manufacturers – Regulated 5V Charge Pump In SOT-23

AIC1845
2. Package Size: A ceramic capacitor with
large volume (0805), gets a lower ESR than
a small one (0603). Therefore, large devices
can improve more transient response than
small ones.
Table 1 lists the recommended components for
AIC1845 application.
Table.1 Bill of Material
Design- Part
Description
ator Type
Vendor
Phone
CELMK212BJ- TAIYO
C_IN
2.2µ
[phone]~9
225MG (X5R) YUDEN
C_FLY
CEEMK212BJ TAIYO
0.22µ
-224KG (X7R) YUDEN
[phone]~9
C_OUT
CELMK212BJ- TAIYO
2.2µ
225MG (X5R) YUDEN
[phone]~9
Power Dissipation
Let’s consider the power dissipation of R_DS-ON
and ESR. Assume that the R_DS-ON of each internal
switching element in AIC1845 is equal and ESR
is the equivalent series resistance of C_FLY (ref to
Fig. 20 and Fig. 21). The approximation of the
power loss of R_DS-ON and ESR are given below:
P_RDS−ON ≅ I_{O2 N-AVE} × 2R_DS−ON × D + I_{O2 FF-AVE} × 2R_DS−ON × (1− D)
=
(
I_IN
2D
)²
×
2R_DS-ON
×
D
+
(
I_OUT
1- D
)²
×
2R_DS-ON
×
(1-
D)
=
(
2I_OUT
2D
)²
×
2R_DS-ON
×
D
+
(
I_OUT
1- D
)²
×
2R_DS-ON
×
(1-
D)
=
I_{O2 UT}
×
(2
D
R_DS-ON )
+
I_{O2 UT}
×
(2
1- D
R_DS-ON )
=
I_{O2 UT}
×
2
D(1-
D)
× R_DS-ON
P_ESR ≅ I_{O2 N−AVE} × ESR × D + I_{O2 FF−AVE} × ESR × (1 − D)
= ( ^IIN )² × ESR × D + ( ^IOUT )² × ESR × (1 − D)
2D
1− D
=
I_{O2 UT}
× ESR
×
1
D
+
I_{O2 UT}
× ESR
×
1
1- D
=
I_{O2 UT}
× ESR
×
1
D(1 -
D)
When the duty cycle is 0.5, the power loss of
switching element is
P_RDS−ON
≅ I_{O2 UT}
×
2
0.5(1 −
0.5)
×
R_{DS - ON}
= I_{O2 UT} × 8R_DS−ON
P_ESR
≅
I_{O2 UT}
× ESR
×
1
0.5(1 −
0.5)
= I_{O2 UT} × 4ESR
In fact, no matter the current is at on state or off
state, it decays exponentially rather than flows
steadily. And the root mean square value of
exponential decay is not equal to that of steady
flow. That is why the approximation comes from.
Let’s treat the charge pump circuit in another
approach and lay the focus on the flying capacitor
C₁. Referring to Fig. 20, when the circuit is at the
on state, the voltage across C₁ is:
V_C-ON (t) = V_IN − 2R_DS−ON × I_ON(t) - ESR × I_ON (t) …(9)
The average of V_C1 during the on state is:
V_{C−ON−AVE} = V_IN − 2R_DS−ON × I_ON−AVE − ESR × I_ON−AVE
……………………….(10)
Similarly, referring to Fig. 21, when the circuit is
at the off state, the voltage of C1 is:
V_C-OFF (t) =
V_OUT − V_IN + 2R_DS-ON × I_OFF (t) + ESR × I_OFF (t)
……………………………(11)
The average of V_C1 during the off state is:
V_{C−OFF−AVE} =
V_OUT − V_IN + 2R_DS−ON × I_OFF−AVE ^.+^...E^..S^...R^{. (}×⁷⁾I_OFF−AVE
………………..(12)
The difference of charge stored in C₁ between on
state and off state is the net charge transferred to
the output in one cycle.
10