LM5145 datasheet(25/70 Pages) TI

25 / 70 page

Configure PFM mode by connecting the PFM/SYNC of the primary to VDDA and the FB of the secondary to

VDDA as shown in Figure 8-7. Configure FPWM mode by connecting PFM/SYNC of the primary and FB of

the secondary both to AGND. An external synchronization signal can be applied to the primary PFM/SYNC

(SYNCIN), and the secondary FB must be configured for FPWM. If an external SYNCIN signal is applied after

start-up while in primary/secondary mode, there is a two-clock cycle delay before the LM5148 locks on to the

external synchronization signal.

Figure 8-7. Schematic Configured for Single-Output Dual-Phase Operation

Primary

Controller

SYNCOUT

EN CH2

EN CH1

Secondary

Controller

PFM/SYNC

EXTCOMP

CNFG

PGOOD/

SYNCOUT

OUT

VDDA

PFM/SYNC

EXTCOMP

CNFG

PGOOD/

SYNCOUT

CNFG1

54.9 k

CNFG2

90.9 k

PGOOD

20 k

FB1

FB2

VDDA

In PFM mode, the

controller enters pulse skipping to reduce the IQ current and improve the light-load efficiency. When this occurs,

the primary controller disables its synchronization clock output, so phase shedding is not supported. In PFM

mode connect the two enable pins together. Phase shedding is supported in FPWM only. In FPWM, enable

or disable the secondary controller as needed to support higher load current or better light-load efficiency,

respectively. When the secondary controller is disabled and then re-enabled, its internal soft start is pulled low

and the LM5148 goes through a normal soft-start turn-on.

When the LM5148 is configured for a single-output dual-phase operation using the internal 3.3-V feedback

resistor divider, the internal bootstrap UV circuit can source current out of the SW pin, charging up the output

capacitors approximately to 3.6 V. If this behavior is undesirable, you can add a 100-kΩ resistor from VOUT to

GND to bleed off the charge on the output capacitors.

For more information, see the Benefits of a Multiphase Buck Converter Technical Brief and Multiphase Buck

Design From Start to Finish Application Report.

www.ti.com

LM5148

SNVSC01 – FEBRUARY 2023

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