7.3.15 Power Good

The TPS548C26 device offers a power-good output on PG pin, which asserts high when the converter output is

within the target. The PG output stays low when the switching is disabled by EN pin or insufficient PVIN level.

The PG output is an open-drain output and must be pulled up externally through a pull-up resistor (usually 10

kΩ). The recommended PG pull-up resistor value is from 1 kΩ to 100 kΩ.

The PG function is activated after VCC voltage level reaches the minimum VCC threshold for a valid PG output

(maximum 1.2V). When VCC is lower than 1.2V, the PG circuit does not have sufficient power supply and

the open-drain output is always high-Z. The power-good function is fully activated after the soft-start ramp is

completed and also the 1 ms PG delay expires.

7.4 Device Functional Modes

7.4.1 Forced Continuous-Conduction Mode

When the operation mode is set to FCCM, the controller operates in continuous conduction mode (CCM) during

light-load conditions. During CCM, the switching frequency maintained to an almost constant level over the entire

load range which is suitable for applications requiring tight control of the switching frequency at the cost of lower

efficiency.

When FCCM is selected, the TPS548C26 device operates at CCM during the whole soft-start period as well as

the nominal operation.

7.4.2 Auto-Skip Eco-mode Light Load Operation

When the operation mode is set to DCM, the device automatically reduces the switching frequency at light-load

conditions to maintain high efficiency. This section describes the operation in detail.

As the output current decreases from heavy load condition, the inductor current also decreases until the rippled

valley of the inductor current touches zero level. Zero level is the boundary between the continuous-conduction

and discontinuous-conduction modes. The synchronous MOSFET turns off when this zero inductor current

is detected. As the load current decreases further, the converter runs into discontinuous-conduction mode

(DCM). The on-time is maintained to a level approximately the same as during continuous-conduction mode

operation so that discharging the output capacitor with a smaller load current to the level of the reference voltage

requires more time. The transition point to the light-load operation IOUT(LL) (for example: the threshold between

continuous- and discontinuous-conduction mode) is calculated as shown in below equation.

( )

(

)

-

´

=

´

´ ´

IN

OUT

OUT

OUT LL

SW

IN

V

V

V

1

I

2

L

f

V

(2)

Where

• fSW is the switching frequency

TI recommends sing low ESR capacitors (such as ceramic capacitor) for skip-mode.

7.4.3 Powering the Device from a 12-V Bus

The device works well when powering from a 12-V bus with a single VIN configuration. As a single VIN

configuration, the internal LDO is powered by the 12-V bus and generates 4.5-V output to bias the internal

analog circuitry and also powers up the gate drives. The VIN input range under this configuration is 4 V to 16 V

for up to 35-A load current. Figure 7-1 shows an example for this single VIN configuration.

VIN and EN are the two signals to enable the part. For start-up sequence, any sequence between the VIN and EN

signals can power the device up correctly.

www.ti.com

TPS548C26

SLVSGM2 – MARCH 2023

Copyright © 2023 Texas Instruments Incorporated

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