LM5171 datasheet(65/89 Pages) TI2

65 / 89 page

Choose CIMONx considering delay and voltage ripple. Here we select:

CIMONx = 10nF

(101)

Then the delay of the monitor is determined by the following time constant:

τIMONx=RIMONx×CIMONx=10kΩ×10ns=100µs

(102)

At full load, the DC component of the monitor voltage is:

VIMONx=2× Imax×RCS

500Ω +50µA ×RIMONx=2× 30A×1mΩ

500Ω +50µA ×10kΩ=2.2V

(103)

Considering the inductor ripple current, the IOUT peak to peak ripple current is:

ΔIMONx=Ipk−pk×RCS

500Ω =23.8A×1mΩ

500Ω =47.6µA

(104)

The RC filter corner frequency is thus given by:

fIMONx= 1

2π×RIMONx×CIMONx= 1

6.28×10kΩ×10nF=1.59kHz

(105)

The resulting peak-to-peak monitor ripple voltage is approximately determined by:

ΔVIMONx=ΔIMONx× RIMONx 1

2i×π×FSW×CIMONx =47.6µA× 10kΩ 1

2i×π×100kHz×10nF =7.5mV (106)

The peak-to-peak monitor ripple voltage is approximately 0.34% of the full load DC monitor voltage. Increasing

CIMONx attenuates the ripple voltage at the cost of higher monitor delay.

8.6.1.2.13 Undervoltage Lockout (UVLO)

The example circuit uses UVLO pin as the Controller enable pin of LM5171-Q1. However, UVLO pin also fulfills

the function of undervoltage lockout, either the 48V rail UVLO, or 12V rail UVLO, or VCC UVLO.

Assume the user implements the 48V rail UVLO, and the low-side resistor RUVLO2 = 10kΩ, the 48V UVLO

release threshold VUVLO = 24V, and UVLO hysteresis is VHYS = 2.4V. Referring to Equation 1, RUVLO1 is given

by:

UVLO

UVLO1

UVLO2

2.5 V

24 V

2.5 V

10 k

86 k

2.5 V

(107)

Select the closest standard resistor of RUVLO1 = 86.6kΩ.

Referring Equation 3, RUVLO3 is found as:

HYS

UVLO1

UVLO3

UVLO1

UVLO2

2.4 V

86.6 k

0.973 k

86.6 k

10 k

(108)

Select the closest standard resistor, RUVLO1 = 976Ω.

If the user chooses to add the capacitor CUVLO = 1nF, it leads to a delay time constant of 10µs to filter possible

noise at the at the UVLO pin.

www.ti.com

LM5171-Q1

SNVSC75B – APRIL 2023 – REVISED SEPTEMBER 2025

Submit Document Feedback

Product Folder Links: LM5171-Q1

LM5171 Datasheet(PDF) 65 Page - Texas Instruments

LM5171 Datasheet(HTML) 65 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 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89

Datasheet Download

Link URL