DC1198A-A Linear Technology, DC1198A-A Datasheet - Page 11

• Manufacturer Part Number: DC1198A-A
• Description: BOARD EVAL LTM4605
• Manufacturer: Linear Technology
• Series: µModuler

Specifications of DC1198A-A

• Design Resources: LTM4605 Spice Model LTM460(5,7) Gerber Files DC1198 Design Files DC1198A-(A,B) Schematic
• Main Purpose: DC/DC, Step Up or Down
• Outputs And Type: 1, Non-Isolated
• Power - Output: -
• Voltage - Output: 12V
• Current - Output: 5A
• Voltage - Input: 4.5 ~ 20V
• Regulator Topology: Buck-Boost
• Frequency - Switching: 300kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LTM4605
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
For a buck converter, the switching duty-cycle can be
estimated as:
Without considering the inductor current ripple, the RMS
current of the input capacitor can be estimated as:
In the above equation, η is the estimated effi ciency of the
power module. C
aluminum capacitor, OS-CON capacitor or high volume
ceramic capacitors. Note the capacitor ripple current rat-
ings are often based on temperature and hours of life. This
makes it advisable to properly derate the input capacitor,
or choose a capacitor rated at a higher temperature than
required. Always contact the capacitor manufacturer for
derating requirements.
Output Capacitors
In boost mode, the discontinuous current shifts from the
input to the output, so the output capacitor C
capable of reducing the output voltage ripple.
For boost and buck modes, the steady ripple due to charg-
ing and discharging the bulk capacitance is given by:
The steady ripple due to the voltage drop across the ESR
(effective series resistance) is given by:
D =
I
V
V
V
V
CIN(RMS)
RIPPLE,BOOST
RIPPLE,BUCK
ESR,BUCK
ESR,BOOST
V
V
OUT
IN
=
= ΔI
I
= I
OUT(MAX)
=
L(MAX)
=
IN
L(MAX)
8 • L • C
η
V
I
OUT(MAX)
OUT
can be a switcher-rated electrolytic
• ESR
• V
• D • (1− D)
• ESR
(
OUT
C
OUT
IN(MAX)
• V
• V
(
• V
IN(MAX)
OUT
OUT
− V
− V
OUT
• f
IN(MIN)
• f
)
2
OUT
)
must be
The LTM4605 is designed for low output voltage ripple.
The bulk output capacitors defi ned as C
with low enough ESR to meet the output voltage ripple
and transient requirements. C
lum capacitor, a low ESR polymer capacitor or a ceramic
capacitor. Multiple capacitors can be placed in parallel to
meet the ESR and RMS current handling requirements.
The typical capacitance is 300μF . Additional output fi ltering
may be required by the system designer, if further reduction
of output ripple or dynamic transient spike is required.
Table 3 shows a matrix of different output voltages and
output capacitors to minimize the voltage droop and
overshoot at a current transient.
Inductor Selection
The inductor is chiefl y decided by the required ripple cur-
rent and the operating frequency. The inductor current
ripple ΔI
inductor current. In the inductor design, the worst cases
in continuous mode are considered as follows:
where:
The inductor should have low DC resistance to reduce the
I
current without saturation. To minimize radiated noise,
use a toroid, pot core or shielded bobbin inductor. Please
refer to Table 3 for the recommended inductors for dif-
ferent cases.
2
R losses, and must be able to handle the peak inductor
f is operating frequency, Hz
Ripple% is allowable inductor current ripple, %
V
V
V
I
L
L
OUT(MAX)
OUT(MAX)
IN(MAX)
OUT
BOOST
BUCK
is output voltage, V
L
≥
is typically set to 20% to 40% of the maximum
≥
is maximum input voltage, V
V
is maximum output load current, A
V
IN(MAX)
is maximum output voltage, V
OUT(MAX)
V
OUT
V
IN
• f • I
• V
• V
(
• f • I
(
IN(MAX)
OUT(MAX)
OUT(MAX)
OUT(MAX)
OUT
− V
can be a low ESR tanta-
• Ripple%
− V
OUT
• Ripple%
LTM4605
IN
)
OUT
)
are chosen
11
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