LM5166 datasheet(42/57 Pages) TI2

42 / 57 page

EN(off)

HYS

UV1

UV2

IN(off)

EN(off)

EN(on)

UV2

UV1

IN(on)

EN(on)

LM5166

SNVSA67B – DECEMBER 2016 – REVISED JUNE 2017

www.ti.com

Product Folder Links: LM5166

Submit Documentation Feedback

8.2.5.2 Detailed Design Procedure

The component selection procedure for this design is quite similar to that of COT designs 1 and 2.

8.2.5.2.1

Peak Current Limit Setting – RILIM

Leave the ILIM pin open circuit to select the 500-mA peak current limit setting for a rated output current of 300

mA. See Table 3.

8.2.5.2.2

Switching Frequency – RRT

Using Equation 4, select a standard 1% resistor value of 169 kΩ to set a switching frequency of 400 kHz.

8.2.5.2.3

Inductor – LF

Choosing a 100-μH inductor in this design results in 150-mA peak-to-peak ripple current at an input voltage of 24

V, equivalent to 50% of the 300-mA rated load current. A larger ripple current design results in improved light-

load efficiency. The peak inductor current at maximum input voltage of 65 V is 424 mA, which is sufficiently

below the LM5166 peak current limit of 500 mA. Select an inductor with saturation current rating well above the

peak current limit setting, and allow for derating of the saturation current at the highest expected operating

temperature.

8.2.5.2.4

Input and Output Capacitors – CIN, COUT

Choose a 4.7-µF, 80-V or 100-V ceramic input capacitor with 1210 footprint. Such a capacitor is typically

available in X7S or X7R dielectric. Based on Equation 24, select a 10-µF, 25-V ceramic output capacitor with

X7R dielectric and 1206 footprint.

8.2.5.2.5

Feedback Resistors – RFB1, RFB2

Select RFB1 of 1 MΩ to minimize quiescent current and improve light-load efficiency in this application. With the

desired output voltage setpoint of 12 V and VFB = 1.223 V, calculate the resistance of RFB2 using Equation 15 as

113.5 kΩ. Choose the closest available standard value of 113 kΩ for RFB2. See Adjustable Output Voltage (FB)

for more detail.

8.2.5.2.6

Ripple Generation Network – RA, CA, CB

Select the ripple injection circuit components RA and CA values using Equation 10 and Equation 11. Choose

capacitor CB using Equation 12 based on a target transient response settling time of 300 µs.

8.2.5.2.7

Undervoltage Lockout Setpoint – RUV1, RUV2, RHYS

Adjust the undervoltage lockout (UVLO) using an externally-connected resistor divider network of RUV1, RUV2, and

RHYS. The UVLO has two thresholds, one for power up when the input voltage is rising and one for power down

or brownouts when the input voltage is falling. The EN rising threshold for the LM5166 is 1.22 V.

Rearranging Equation 16 and Equation 17, the expressions to calculate RUV2 and RHYS are as follows:

(32)

(33)

Choose RUV1 as 10 MΩ to minimize input quiescent current. Given the desired input voltage UVLO thresholds of

20 V and 18 V, calculate the resistance of RUV2 and RHYS as 649 kΩ and 14 kΩ, respectively. See Precision

Enable (EN) and Hysteresis (HYS) for more detail.

8.2.5.2.8

Soft Start – CSS

Install a 47-nF capacitor from SS to GND for a soft-start time of 6 ms.

LM5166 Datasheet(PDF) 42 Page - Texas Instruments

LM5166 Datasheet(HTML) 42 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

Datasheet Download

Link URL