LTM4613 datasheet(11/30 Pages) LINER

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LTM4613

4613fd

For more information www.linear.com/LTM4613

APPLICATIONS INFORMATION

Figure 2. Operating Frequency vs Output Voltage

Operating Frequency

The operating frequency of the LTM4613 is optimized to

achieve the compact package size and the minimum

output ripple voltage while still keeping high efficiency.

As shown in Figure 2, the frequency is linearly increased

with larger output voltages to keep the low output cur-

rent ripple. Figure 3 shows the inductor current ripple ∆I

with different output voltages. In most applications, no

additional frequency adjusting is required.

If lower output ripple is required, the operating frequency

f can be increased by adding a resistor RfSET between fSET

pin and SGND, as shown in Figure 19.

f =

VOUT

1.5•10−10 RfSET ||133k

(

)

[Hz]

Figure 3. Pk-Pk Inductor Current Ripple vs Output Voltage

Table 1. RFB Standard 1% Resistor Values vs VOUT

VOUT (V)

3.3

RFB (kΩ) 22.1 13.7 11.0 8.06 6.34 5.23 4.42 4.12

The MPGM pin programs a current that when multiplied

by an internal 10k resistor sets up the 0.6V reference ±

offset for margining. A 1.18V reference divided by the

RPGM resistor on the MPGM pin programs the current.

Calculate VOUT(MARGIN):

VOUT(MARGIN) =

%VOUT

100

• VOUT

Where %VOUT is the percentage of VOUT to be margined,

and VOUT(MARGIN) is the margin quantity in volts:

RPGM =

VOUT

0.6V

•

1.18V

VOUT(MARGIN)

•10k

Where RPGM is the resistor value to place on the MPGM

pin to ground.

The margining voltage, VOUT(MARGIN), will be added or

subtracted from the nominal output voltage as determined

by the state of the MARG0 and MARG1 pins. See the truth

table below:

MARG1

MARG0

MODE

LOW

NO MARGIN

LOW

HIGH

MARGIN UP

HIGH

LOW

MARGIN DOWN

HIGH

NO MARGIN

Parallel Operation

The LTM4613 device is an inherently current mode con-

trolled device. This allows the paralleled modules to have

very good current sharing and balanced thermals on the

design.Figure21showsaschematicoftheparalleldesign.

The voltage feedback equation changes with the variable

N as modules are paralleled:

RFB =

100k

VOUT

0.6V

− 1

where N is the number of paralleled modules.

OUTPUT VOLTAGE (V)

400

1000

4613 F02

200

800

600

OUTPUT VOLTAGE (V)

4613 F03

VIN = 16V

VIN = 24V

VIN = 28V

VIN = 36V

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