LTM4607 datasheet(9/24 Pages) LINER

9 / 24 page

LTM4607

4607f

OPERATION

Power Module Description

The LTM4607 is a non-isolated buck-boost DC/DC power

supply. It can deliver a wide range output voltage from

0.8V to 24V over a wide input range from 4.5V to 36V,

by only adding the sensing resistor, inductor and some

external input and output capacitors. It provides precisely

regulated output voltage programmable via one external

resistor. The typical application schematic is shown in

Figure 18.

The LTM4607 has an integrated current mode buck-boost

control, ultralow RDS(ON) FETs with fast switching speed

and integrated Schottky diodes. With current mode control

and internal feedback loop compensation, the LTM4607

module has sufﬁcient stability margins and good transient

performance under a wide range of operating conditions

and with a wide range of output capacitors. The frequency

of LTM4607 can be operated from 200kHz to 400kHz by

setting the voltage on the PLLFLTR pin. Alternatively, its

frequency can be synchronized by the input clock signal

from the PLLIN pin. The typical switching frequency is

400kHz.

The Burst Mode and skip-cycle mode operations can

be enabled at light loads in the LTM4607 to improve its

efﬁciency, while the forced continuous mode and discon-

tinuous mode operations are used for constant frequency

applications. Foldback current limiting is activated in an

overcurrent condition as VFB drops. Internal overvoltage

and undervoltage comparators pull the open-drain PGOOD

output low if the output feedback voltage exits the ±10%

window around the regulation point. Pulling the RUN pin

below 1.6V forces the controller into its shutdown state.

If an external bias supply is applied on the EXTVCC pin, then

an efﬁciency improvement will occur due to the reduced

power loss in the internal linear regulator. This is especially

true at the higher input voltage range.

APPLICATIONS INFORMATION

The typical LTM4607 application circuit is shown in

Figure 18. External component selection is primarily

determined by the maximum load current and output

voltage. Refer to Table 3 for speciﬁc external capacitor

requirements for a particular application.

Output Voltage Programming

The PWM controller has an internal 0.8V±1% reference

voltage. As shown in the Block Diagram, a 100k 0.5%

internal feedback resistor connects VOUT and VFB pins

together. Adding a resistor RFB from the VFB pin to the

SGND pin programs the output voltage:

OUT

0 8

100

.•

Table 1. RFB Resistor (0.5%) vs Output Voltage

VOUT

0.8V

1.5V

2.5V

3.3V

RFB

Open

115k

47.5k

32.4k

19.1k

15.4k

11k

VOUT

10V

12V

15V

16V

20V

24V

RFB

9.76k

8.66k

7.15k

5.62k

5.23k

4.12k

3.4k

Operation Frequency Selection

The LTM4607 uses current mode control architecture at

constant switching frequency, which is determined by the

internal oscillator’s capacitor. This internal capacitor is

charged by a ﬁxed current plus an additional current that

is proportional to the voltage applied to the PLLFLTR pin.

The PLLFLTR pin can be grounded to lower the frequency

to 200kHz or tied to 2.4V to yield approximately 400kHz.

When PLLIN is left open, the PLLFLTR pin goes low, forc-

ing the oscillator to its minimum frequency.

A graph for the voltage applied to the PLLFLTR pin vs

frequency is given in Figure 2. As the operating frequency

increases, the gate charge losses will be higher, thus the

efﬁciency is low. The maximum switching frequency is

approximately 400kHz.

FREQUENCY SYNCHRONIZATION

The LTM4607 can also be synchronized to an external

source via the PLLIN pin instead of adjusting the voltage on

the PLLFLTR pin directly. The power module has a phase-

LTM4607 数据表(PDF) 9 Page - Linear Technology

LTM4607 数据表(HTML) 9 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

数据表下载