MP2364DF-LF-Z Monolithic Power Systems, MP2364DF-LF-Z Datasheet - Page 6

• Manufacturer Part Number: MP2364DF-LF-Z
• Description: Up/Down Conv Mixer 4.75V to 23V 20-Pin TSSOP EP T/R
• Manufacturer: Monolithic Power Systems

Specifications of MP2364DF-LF-Z

• Package: 20TSSOP EP

APPLICATION INFORMATION
COMPONENT SELECTION
The MP2364 has two channels: A and B. The
following formulas are used for component
selection of both channels. Refer to
components with reference “A” for channel A,
and components with reference “B” for channel
B, respectively, as indicated in Figure 3 (i.e. –
R1A for Channel A and R1B for Channel B).
Setting the Output Voltage
The output voltage is set using a resistive
voltage divider from the output voltage to FB pin.
The voltage divider divides the output voltage
down to the feedback voltage by the ratio:
Thus the output voltage is:
Where V
the output voltage
A typical value for R2 can be as high as 100kΩ,
but a typical value is 10kΩ. Using that value, R1
is determined by:
For example, for a 3.3V output voltage, R2 is
10kΩ, and R1 is 25.9kΩ.
Inductor
The inductor is required to supply constant
current to the output load while being driven by
the switched input voltage. A larger value
inductor will result in less ripple current that will
result in lower output ripple voltage. However,
the larger value inductor will have a larger
physical size, higher series resistance, and/or
lower saturation current. A good rule for
determining the inductance to use is to allow
the peak-to-peak ripple current in the inductor
to be approximately 30% of the maximum
switch current limit. Also, make sure that the
peak inductor current is below the maximum
MP2364 Rev. 1.6
1/22/2010
FB
is the feedback voltage and V
V
R
OUT
V
1
FB
=
=
R
=
. 0
2
V
92
×
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
OUT
(
V
. 0
V
×
R
92
OUT
1
R
R
V
+
1
2
R
R
+
−
2
2
R
) 1
2
MP2364 — DUAL 1.5A, 23V, 1.4MHz STEP-DOWN CONVERTER
© 2010 MPS. All Rights Reserved.
www.MonolithicPower.com
OUT
is
switch current limit. The inductance value can
be calculated by:
Where V
switching frequency, and ∆I
peak inductor ripple current.
Choose an inductor that will not saturate under
the maximum inductor peak current.
The peak inductor current can be calculated by:
Where I
Output Rectifier Diode
The output rectifier diode supplies the current to
the inductor when the high-side switch is off. To
reduce losses due to the diode forward voltage
and recovery times, use a Schottky diode.
Choose a diode whose maximum reverse
voltage rating is greater than the maximum
input voltage, and whose current rating is
greater than the maximum load current.
Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required
to supply the AC current to the step-down
converter while maintaining the DC input
voltage. Use low ESR capacitors for the best
performance. Ceramic capacitors are preferred,
but tantalum or low-ESR electrolytic capacitors
may also suffice.
Since the input capacitor (C1) absorbs the input
switching current it requires an adequate ripple
current rating. The RMS current in the input
capacitor can be estimated by:
The worst-case condition occurs at V
where:
LOAD
I
LP
IN
I
C
=
1
is the load current.
1 L
I
is the input voltage, f
=
LOAD
I
=
LOAD
f
S
+
V
I
×
OUT
2
C
×
1
∆I
×
V
=
L
f
OUT
S
V
×
I
V
×
LOAD
OUT
⎛
⎜
⎜
⎝
IN
L
2
1
1
−
×
×
⎛
⎜
⎜
⎝
V
1
⎛
⎜ ⎜
⎝
L
V
OUT
1
−
IN
−
V
is the peak-to-
V
OUT
V
⎞
⎟
⎟
⎠
IN
V
OUT
IN
⎞
⎟
⎟
⎠
IN
⎞
⎟ ⎟
⎠
S
= 2V
is the
OUT
6
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