LTM4605 データシートの表示（PDF） - Linear Technology

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LTM4605

High Efficiency Buck-Boost DC/DC uModule

Linear Technology 

LTM4605

OPERATION

Power Module Description

The LTM4605 is a non-isolated buck-boost DC/DC power

supply. It can deliver a wide range output voltage from

0.8V to 16V over a wide input range from 4.5V to 20V,

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 16.

The LTM4605 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 LTM4605

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 LTM4605 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 LTM4605 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 LTM4605 application circuit is shown in

Figure 16. 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:

VOUT

=

0.8V

•

100k + RFB

RFB

Table 1. RFB Resistor (0.5%) vs Various Output Voltages

VOUT 0.8V 1.5V 2.5V 3.3V

5V

6V

RFB Open 115k 47.5k 32.4k 19k 15.4k

VOUT

8V

9V

10V 12V 15V 16V

RFB

11k 9.76k 8.66k 7.15k 5.62k 5.23k

Operation Frequency Selection

The LTM4605 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.

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9

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