out

in

out

out

out

s

ripple

(V

V ) I

C

V

F

V

-

=

´

´

11

TPS61165

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SLVS790D – NOVEMBER 2007 – REVISED APRIL 2016

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Application Information (continued)

Inductor values can have ±20% tolerance with no current bias. When the inductor current approaches saturation

level, its inductance can decrease 20% to 35% from the 0A value depending on how the inductor vendor defines

saturation current. Using an inductor with a smaller inductance value forces discontinuous PWM when the

inductor current ramps down to zero before the end of each switching cycle. This reduces the maximum output

current of the boost convert, causes large input voltage ripple, and reduces efficiency. Large inductance value

provides much more output current and higher conversion efficiency. For these reasons, a 10-

μH to 22-μH

inductor value range is recommended. A 22-

μH inductor optimized the efficiency for most application while

maintaining low inductor peak to peak ripple. Table 2 lists the recommended inductor for the TPS61165. When

recommending inductor value, the factory has considered –40% and 20% tolerance from its nominal value.

TPS61165 has built-in slope compensation to avoid subharmonic oscillation associated with current mode

control. If the inductor value is lower than 10

μH, the slope compensation may not be adequate, and the loop can

be unstable. Therefore, customers need to verify the inductor in their application if it is different from the

recommended values.

Table 2. Recommended Inductors for TPS61165

PART NUMBER

L

(

μH)

DCR MAX

(m

Ω)

SATURATION CURRENT (A)

SIZE

(L × W × H mm)

VENDOR

A915_Y-100M

10

90

1.3

5.2 × 5.2 × 3.0

TOKO

VLCF5020T-100M1R1-1

10

237

1.1

5 × 5 × 2.0

TDK

CDRH4D22/HP

10

144

1.2

5 × 5 × 2.4

Sumida

LQH43PN100MR0

10

247

0.84

4.5 × 3.2 × 2.0

Murata

9.1.3 Schottky Diode Selection

The high switching frequency of the TPS61165 demands a high-speed rectification for optimum efficiency.

Ensure that the average and peak current rating of the diode exceeds the average output current and peak

inductor current. In addition, the reverse breakdown voltage of the diode must exceed the open LED protection

voltage. The ONSemi MBR0540 and the ZETEX ZHCS400 are recommended for TPS61165.

9.1.4 Compensation Capacitor Selection

The compensation capacitor C3 (see Functional Block Diagram), connected from COMP pin to GND, is used to

stabilize the feedback loop of the TPS61165. A 220-nF ceramic capacitor is suitable for most applications.

9.1.5 Input and Output Capacitor Selection

The output capacitor is mainly selected to meet the requirements for the output ripple and loop stability. This

ripple voltage is related to the capacitor’s capacitance and its equivalent series resistance (ESR). Assuming a

capacitor with zero ESR, the minimum capacitance needed for a given ripple can be calculated as shown in

Equation 4.

where

•

(4)

The additional output ripple component caused by ESR is calculated as shown in Equation 4.

(5)

electrolytic capacitors are used.

Care must be taken when evaluating a ceramic capacitors derating under dc bias, aging and AC signal. For

example, larger form factor capacitors (in 1206 size) have self-resonant frequencies in the range of the switching

frequency. So the effective capacitance is significantly lower. The dc bias can also significantly reduce

capacitance. Ceramic capacitors can loss as much as 50% of its capacitance at its rated voltage. Therefore,

leave the margin on the voltage rating to ensure adequate capacitance at the required output voltage.