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ADP5070AREZ-R7 Datasheet(PDF) 20 Page - Analog Devices

Part # ADP5070AREZ-R7
Description  Independent Positive and Negative Outputs
PDF  28 Pages
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Manufacturer  AD [Analog Devices]
Direct Link  http://www.analog.com
Logo AD - Analog Devices

ADP5070AREZ-R7 Datasheet(HTML) 20 Page - Analog Devices

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Data Sheet
ADP5070
Rev. A | Page 19 of 27
For the inductor ripple current in continuous conduction mode
(CCM) operation, the input (VIN) and output (VPOS) voltages
determine the switch duty cycle (DUTY1) by
+
+
−
=
DIODE1
POS
DIODE1
IN
POS
1
V
V
V
V
V
DUTY
where VDIODE1 is the forward voltage drop of the Schottky diode
(D1).
The dc input current in CCM (IIN) can be determined by the
following equation:
)
1
(
1
OUT1
IN
DUTY
I
I
−
=
Using the duty cycle (DUTY1) and switching frequency (fSW),
determine the on time (tON1) using the following equation:
SW
1
ON1
f
DUTY
t
=
The inductor ripple current (∆IL1) in steady state is calculated by
L1
t
V
I
ON1
IN
L1
×
=
∆
Solve for the inductance value (L1) using the following
equation:
L1
ON1
IN
I
t
V
L1
∆
×
=
Assuming an inductor ripple current of 30% of the maximum
dc input current results in
OUT1
1
ON1
IN
I
DUTY
t
V
L1
×
−
×
×
=
3
.
0
)
1
(
Ensure that the peak inductor current (the maximum input
current plus half the inductor ripple current) is below the rated
saturation current of the inductor. Likewise, ensure that the
maximum rated rms current of the inductor is greater than the
maximum dc input current to the regulator.
When the ADP5070 boost regulator is operated in CCM at duty
cycles greater than 50%, slope compensation is required to
stabilize the current mode loop. This slope compensation is
built in to the ADP5070. For stable current mode operation,
ensure that the selected inductance is equal to or greater than
the minimum calculated inductance, LMIN1, for the application
parameters in the following equation:
−
−
×
=
>
33
.
0
)
1
(
27
.
0
1
IN
MIN1
DUTY
V
L
L1
(µH)
Table 10 suggests a series of inductors to use with the ADP5070
boost regulator.
Inductor Selection for the Inverting Regulator
The inductor stores energy during the on time of the power
switch, and transfers that energy to the output through the
output rectifier during the off time. To balance the tradeoffs
between small inductor current ripple and efficiency, inductance
values in the range of 1 µH to 22 µH are recommended. In
general, lower inductance values have higher saturation current
and lower series resistance for a given physical size. However,
lower inductance results in a higher peak current that can lead
to reduced efficiency and greater input and/or output ripple and
noise. A peak-to-peak inductor ripple current close to 30% of
the maximum dc current in the inductor typically yields an
optimal compromise.
For the inductor ripple current in continuous conduction mode
(CCM) operation, the input (VIN) and output (VNEG) voltages
determine the switch duty cycle (DUTY2) by
+
+
+
=
DIODE2
NEG
IN
DIODE2
NEG
2
V
V
V
V
V
DUTY
|
|
|
|
where VDIODE2 is the forward voltage drop of the Schottky diode
(D2).
The dc current in the inductor in CCM (IL2) can be determined
by the following equation:
)
1
(
2
OUT2
L2
DUTY
I
I
−
=
Using the duty cycle (DUTY2) and switching frequency (fSW),
determine the on time (tON2) by the following equation:
SW
2
ON2
f
DUTY
t
=
The inductor ripple current (∆IL2) in steady state is calculated by
L2
t
V
I
ON2
IN
L2
×
=
∆
Solve for the inductance value (L2) by the following equation:
L2
ON2
IN
I
t
V
L2
∆
×
=
Assuming an inductor ripple current of 30% of the maximum
dc current in the inductor results in
OUT2
2
ON2
IN
I
DUTY
t
V
L2
×
−
×
×
=
3
.
0
)
1
(
Ensure that the peak inductor current (the maximum input
current plus half the inductor ripple current) is below the rated
saturation current of the inductor. Likewise, ensure that the
maximum rated rms current of the inductor is greater than the
maximum dc input current to the regulator.



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