MP2315 – 24V, 3A SYNC STEP DOWN CONVERTER
APPLICATION INFORMATION
COMPONENT SELECTION
Setting the Output Voltage
Choose inductor current to be approximately
30% of the maximum load current. The maximum
inductor peak current is:
The external resistor divider is used to set the
output voltage (see Typical Application on page
1). The feedback resistor R1 also sets the
feedback loop bandwidth with the internal
compensation capacitor (see Typical Application
on page 1). R2 is then given by:
IL
IL(MAX) ILOAD
2
Under light load conditions below 100mA, larger
inductance is recommended for improved
efficiency.
R1
R2
Setting the AAM Voltage
V
OUT
The AAM voltage is used to setting the transition
point from AAM to CCM. It should be chosen to
provide the best combination of efficiency,
stability, ripple, and transient.
1
0.8V
The T-type network is highly recommended, as
Figure 4 shows.
If the AAM voltage is set lower, then stability and
ripple improves, but efficiency during AAM mode
and transient degrades. Likewise, if the AAM
voltage is set higher, then the efficiency during
AAM and transient improves, but stability and
ripple degrades. So the optimal balance point of
AAM voltage for good efficiency, stability, ripple
and transient should be found out.
R1
RT
8
FB
VOUT
R2
Figure 4— T-type Network
Table 1 lists the recommended T-type resistors
value for common output voltages.
Adjust the AAM threshold by connecting a
resistor from AAM pin to ground. Take Figure 5
as reference. An internal 6.2µA current source
charges the external resistor.
Table 1—Resistor Selection for Common
Output Voltages
VOUT(V) R1(kΩ) R2(kΩ) Rt(kΩ) Lo(µH) Co(µF)
1.05
1.2
1.8
2.5
3.3
5
20.5
20.5
40.2
40.2
40.2
40.2
62
100
75
1.5
1.8
2.2
3.3
4.2
5.5
44
44
44
44
44
44
1
39.2
31.6
18.7
12.7
7.5
AAM
59
40.2
33
4
20
Figure 5—AAM Network
Generally, R4 is then given by:
VAAM=R4 x 6.2uA
Selecting the Inductor
A 1µH to 10µH inductor with a DC current rating
of at least 25% percent higher than the maximum
load current is recommended for most
applications. For highest efficiency, the inductor
DC resistance should be less than 15mꢀ. For
most designs, the inductance value can be
derived from the following equation.
The optimized AAM can be got from Figure 6.
VOUT (V VOUT
)
IN
L1
V IL fOSC
IN
Where ΔIL is the inductor ripple current.
MP2315 Rev. 1.01
1/8/2014
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
12
MIPS [ MIPS TECHNOLOGIES, INC. ]
