LM5145 datasheet(18/60 Pages) TI2

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RUV2

RUV1

Enable

comparator

11µA

VCC

VIN

Figure 6-3. Programmable Input Voltage UVLO Turn-On

6.3.4 Power-Good Monitor (PG)

The LM25139 includes an output voltage monitoring signal for VOUT to simplify sequencing and supervision.

The power-good signal is used for start-up sequencing of downstream converters, fault protection, and output

monitoring. The power-good output (PG) switches to a high impedance open-drain state when the output voltage

is in regulation. The PG switches low when the output voltage drops below the lower power-good threshold

(92% typical) or rises above the upper power-good threshold (110% typical). A 25µs deglitch filter prevents false

tripping of the PG during transients. TI recommends a pullup resistor of 100kΩ (typical) from PG to the relevant

logic rail.

6.3.5 Switching Frequency (RT)

Program the LM25139 oscillator with a resistor from RT to AGND to set an oscillator frequency between 100kHz

and 3.2MHz. Use Equation 4 to calculate the RT resistance for a given switching frequency.

RTkΩ = 23759

FSWkHz −0.72

(4)

If the oscillator frequency is set with a resistor from RT to AGND, DRSS is disabled. To enable DRSS, use

Equation 4 for the oscillator frequency and connect the resistor from RT to VCC.

6.3.6 Dual Random Spread Spectrum (DRSS)

LM25139 provides a digital spread spectrum, which reduces the EMI of the power supply over a wide

frequency range. DRSS combines a low-frequency triangular modulation profile with a high frequency cycle-

by-cycle random modulation profile. The low-frequency triangular modulation improves performance in lower

radio-frequency bands, while the high-frequency random modulation improves performance in higher radio

frequency bands.

Spread spectrum works by converting a narrowband signal into a wideband signal that spreads the energy over

multiple frequencies. Because industry standards require different EMI receiver resolution bandwidth (RBW)

settings for different frequency bands, the RBW has an impact on the spread spectrum performance. DRSS

is able to simultaneously improve the EMI performance in the low and high RBWs using the low-frequency

triangular modulation profile and at high frequency cycle-by-cycle random modulation, respectively. DRSS can

reduce conducted emissions up to 15dBμV in the low-frequency band (150kHz to 30MHz) and 5dBμV in the

high-frequency band (30MHz to 108MHz).

To enable DRSS, connect a resistor from RT pin to VCC.

LM25139

SLVSJ80 – OCTOBER 2025

www.ti.com

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