LTM4607 datasheet(14/24 Pages) LINER

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LTM4607

4607f

APPLICATIONS INFORMATION

at buck mode, we can get the current ripple ratio of the

current ripple ΔIL to the maximum inductor current IL as

follows:

ΔIL

IN –VOUT )• VOUT

IN •L • f •P

Figure 3. shows the current ripple ratio at different input

voltages based on the inductor values: 2.5μH, 3.3μH, 4.7μH

and 6μH. If we need about 40% ripple current ratio at all

inputs, the 4.7μH inductor can be selected.

At buck mode, sensing resistor selection is based on

the maximum output current and the allowed maximum

sensing threshold 130mV.

SENSE =

2 • 130mV

2• (P / V

OUT ) −ΔIL

Consider the safety margin about 30%, we can choose

the sensing resistor as 9mΩ.

For the input capacitor, use a low ESR sized capacitor to

handle the maximum RMS current. Input capacitors are

required to be placed adjacent to the module. In Figure

16, the 10μF ceramic input capacitors are selected for

their ability to handle the large RMS current into the

converter. The 100μF bulk capacitor is only needed if the

input source impedance is compromised by long inductive

leads or traces.

For the output capacitor, the output voltage ripple and

transient requirements require low ESR capacitors. If

assuming that the ESR dominates the output ripple, the

output ripple is as follows:

ΔVOUT(P-P) = ESR • ΔIL

If a total low ESR of about 5mΩ is chosen for output ca-

pacitors, the maximum output ripple of 21.5mV occurs at

the input voltage of 36V with the current ripple at 4.3A.

Boost Mode Operation

For boost mode operation, use input voltage VIN = 5V to

12V, VOUT = 12V and f = 400kHz.

Set the PLLFLTR pin and RFB as in buck mode.

If the maximum output power P is 60W at boost mode

and the module efﬁciency η is about 95%, we can get

the current ripple ratio of the current ripple ΔIL to the

maximum inductor current IL as follows:

ΔIL

OUT − VIN )• VIN

2η

OUT •L • f •P

Figure 4 shows the current ripple ratio at different input

voltages based on the inductor values: 1.5μH, 2.5μH,

3.3μH and 4.7μH. If we need 30% ripple current ratio at

all inputs, the 3.3μH inductor can be selected.

At boost mode, sensing resistor selection is based on

the maximum input current and the allowed maximum

sensing threshold 160mV.

SENSE =

2 • 160mV

2•

η •VIN(MIN)

+ ΔIL

Consider the safety margin about 30%, we can choose

the sensing resistor as 7mΩ.

Figure 3. Current Ripple Ratio at Different Inputs for Buck Mode

INPUT VOLTAGE VIN (V)

0.8

0.6

2.5μH

3.3μH

6μH

0.4

0.2

4607 F03

4.7μH

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