PLM5177DCPR datasheet(21/54 Pages) TI

21 / 54 page

VT+( Sleep)

Inducto r

Curren t

Output Voltage

Sing le Pulse

Slee p

VO(nom)

Figure 8-5. Timing Diagram for the Power Save Mode

8.3.3 Power-On Reset (POR System)

The integrated power-on reset system provides power to all internal functional circuits other than the gate drivers

and handles the supervision for the internal logic. The low quiescent current design of this block enables an

extremely low shutdown current of the whole system. There is a power ORing between the VIN and BIAS pin for

the POR system to ensure LM5177 functionality even under extreme operation conditions, like an output or input

short.

Once the voltage on VIN or BIAS rises above the POR threshold, the device logic starts the initialization process

and is continuously monitoring the EN/UVLO pin to start the converter operation. To avoid any brownout, the

POR system contains a voltage detection (VDET) for the VIN pin. This function additionally supervises the input

voltage and ensures the power stage operation is blocked outside.

8.3.4 Supply Voltage Selection – VMAX Switch

There are two pins to supply the LM5177 internal voltage regulators. Due to the internal supply voltage selection

circuit, the device can reduce the power dissipation by ensuring a seamless operation at low input or output

voltages as well as in transient operating conditions like an output short. The VMAX switch selects the pin

with the lower voltage from the VIN or BIAS pin once the voltage on both is above the switch-over threshold

(VT(VCC, SUP)). If one pin voltage is lower than the threshold, the other supply pin is selected. And if both pins are

lower than the switch-over threshold, the higher voltage of VIN or BIAS is selected as supply. The following are

common configurations for the supply pins:

• The VIN pin is connected to the supply voltage. The BIAS pin is connected to VO. During start-up, that is as

long as the output voltage is not higher than the supply switch-over threshold, the VIN supplies the internal

regulators. Once VO is high enough, the supply current comes from the BIAS pin.

• Both the VIN pin and the BIAS pin are connected together to the input supply voltage. This configuration is

often used in applications where the input supply voltage is usually lower or equal than the output voltage.

As the BIAS pin is connected to the input voltage, the device has the full current capability of the internal

regulators at low input voltages for start-up.

• The VIN is connected to the input supply voltage and the BIAS pin is connected to an auxiliary supply

(for example, an existing 12-V DC/DC converter). This configuration is commonly used at high voltage

applications on the input and output voltages where the power dissipation over the integrated linear

regulators must be further minimized.

VIN

BIAS

Sup ply Vo ltag e S electio n

to Internal

Regula tors

Figure 8-6. VMAX Supply Scenario 1

www.ti.com

LM5177

SNVSBU4A – JUNE 2022 – REVISED OCTOBER 2022

Submit Document Feedback

Product Folder Links: LM5177

PLM5177DCPR Datasheet(PDF) 21 Page - Texas Instruments

PLM5177DCPR Datasheet(HTML) 21 Page - Texas Instruments

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 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

Datasheet Download

Link URL