LM5145 datasheet(24/74 Pages) TI2

24 / 74 page

The configuration settings are latched and cannot be changed until the LM5137 is powered down with the VCC

voltage decreasing below the falling UVLO threshold, and then powered up again with VCC above 3.8V.

Alternatively, set the output voltage with an external resistor divider from the output to AGND. The FB regulation

voltage is 0.8V, and the output voltage setpoint range is from 0.8V to 60V. Use Equation 4 to calculate the upper

and lower feedback resistors, designated RFB1 and RFB2, respectively. See Figure 7-4.

OUT

FB1

FB2

REF

(4)

A recommended starting value for RFB2 is between 10kΩ and 20kΩ.

VOUT1

COMP1

FB1

VREF

gm = 600 S

COUT1

LO1

RFB1

RFB2

VIN

RCOMP1

CCOMP1

CHF1

–

AGND

Figure 7-4. Voltage Loop With Adjustable Output Setting

If high light-load efficiency is required, take care when selecting the external resistors. The current consumption

of the external divider adds to the LM5137 sleep current. The divider current reflected to VIN scales by the ratio

of VOUT/VIN.

7.3.10 Error Amplifier and PWM Comparator (FB1, FB2, COMP1, COMP2)

Each channel of the LM5137 has an independent high-gain transconductance amplifier that generates an

error current proportional to the difference between the feedback voltage and an internal precision reference

(0.8V). The output of the transconductance amplifier connects to the respective COMP pin, allowing the user to

provide external control loop compensation. TI generally recommends a type-II compensation network for peak

current-mode control. The HO1/2 and LO1/2 driver outputs can be disabled if COMP1/2 is pulled below 100mV.

7.3.10.1 Slope Compensation

The LM5137 provides internal slope compensation for stable operation with peak current-mode control and a

duty cycle greater than 50%. Use Equation 5 to calculate the buck inductance to provide a slope compensation

contribution equal to one times the inductor current downslope.

(5)

• A lower inductance value generally increases the peak-to-peak inductor ripple current, which minimizes size

and cost, and improves transient response at the cost of reduced light-load efficiency due to higher cores

losses and peak currents.

• A higher inductance value generally decreases the peak-to-peak inductor ripple current, reducing switch peak

and RMS currents at the cost of requiring larger output capacitors to meet load-transient specifications.

LM5137

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LM5145 Datasheet(PDF) 24 Page - Texas Instruments

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