LP38853_15 datasheet(13/30 Pages) TI1

13 / 30 page

= V

ADJ

OUT

LP38853

www.ti.com

SNVS335E – DECEMBER 2006 – REVISED NOVEMBER 2015

Feature Description (continued)

Figure 22. Typical CSS vs COUT Values

The CSS capacitor must be connected to a clean ground path back to the device ground pin. No components,

other than CSS, must be connected to the SS pin, as there could be adverse effects to VOUT.

If the soft-start function is not needed the SS pin must be left open, although some minimal capacitance value is

always recommended.

7.3.5 Setting The Output Voltage

The output voltage is set using the external resistive divider R1 and R2 (see Figure 23). The output voltage is

given by Equation 2:

(2)

The resistors used for R1 and R2 must be high quality, tight tolerance, and with matching temperature

coefficients. It is important to remember that, although the value of VADJ is specified, the use of low-quality

resistors for R1 and R2 can easily produce a VOUT value that is unacceptable.

It is recommended that the values selected for R1 and R2 are such that the parallel value is less than 10 k

Ω.

This is to prevent internal parasitic capacitances on the ADJ pin from interfering with the FZ pole set by R1 and

CFF.

((R1 × R2) / (R1 + R2) )

≤ 10 kΩ

(3)

Table 1 lists some suggested, best fit, standard ±1% resistor values for R1 and R2, and a standard ±10%

capacitor values for CFF, for a range of VOUT values. Other values of R1, R2, and CFF are available that give

LP38853 数据表(PDF) 13 Page - Texas Instruments