LP55231 datasheet(47/59 Pages) TI2

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LP55231

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SNOSCR5D – MARCH 2013 – REVISED DECEMBER 2016

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Typical Applications (continued)

8.2.1.1 Design Requirements

DESIGN PARAMETER

EXAMPLE VALUE

Input voltage range

2.7 V to 5.5 V

LED VF (maximum)

3.6 V

LED current

25.5 mA maximum

Input capacitor

CIN1 = CIN2 = 1 μF

Output capacitor

COUT1 = COUT2 = 1 μF

Charge pump fly capacitors

C1 = C2 = C3 = C4 = 0.47 μF

Charge pump mode

1.5× or automatic

8.2.1.2 Detailed Design Procedure

The LP55231 requires 4 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors

are recommended. Tantalum and aluminium capacitors are not recommended because of their high ESR. For

the flying capacitors (C1 and C2) multi-layer ceramic capacitors must always be used. These capacitors are

small, inexpensive and have very low equivalent series resistance (ESR < 20 m typical). Ceramic capacitors with

X7R or X5R temperature characteristic are preferred for use with the LP55231. These capacitors have tight

capacitance tolerance (as good as ±10%) and hold their value over temperature (X7R: ±15% over

−55°C to

+125°C; X5R: ±15% over

−55°C to +85°C). Capacitors with Y5V or Z5U temperature characteristic are generally

not recommended for use with the LP55231. Capacitors with these temperature characteristics typically have

wide capacitance tolerance (80%,

−20%) and vary significantly over temperature (Y5V: 22%, −82% over −30°C

to +85°C range; Z5U: 22%,

−56% over 10°C to 85°C range). Under some conditions, a nominal 1-µF Y5V or Z5U

capacitor could have a capacitance of only 0.1 µF. Such detrimental deviation is likely to cause Y5V and Z5U

capacitors to fail to meet the minimum capacitance requirements of the LP55231.

For proper operation it is necessary to have at least 0.24 μF of effective capacitance for each of the flying

capacitors under all operating conditions. The output capacitor COUT directly affects the magnitude of the output

ripple voltage. In general, the higher the value of COUT, the lower the output ripples magnitude. For proper

operation it is recommended to have at least 0.50 μF of effective capacitance for CIN and COUT under all

operating conditions. The voltage rating of all four capacitors should be 6.3 V; 10 V is recommended.

Table 9 lists suitable external components from some leading ceramic capacitor manufacturers. TI strongly

recommends that the LP55231 circuit be thoroughly evaluated early in the design-in process with the mass-

production capacitors of choice to help ensure that any variability in capacitance does not negatively impact

circuit performance.

Table 9. Suitable External Components

MODEL

TYPE

VENDOR

VOLTAGE RATING (V)

PACKAGE SIZE

1 µF for COUT and CIN

C1005X5R1A105K

Ceramic X5R

TDK

0402

LMK105BJ105KV-F

Ceramic X5R

Taiyo Yuden

0402

ECJ0EB1A105M

Ceramic X5R

Panasonic

0402

ECJUVBPA105M

Ceramic X5R , array of

two

Panasonic

0504

0.47 µF for C1 and C2

C1005X5R1A474K

Ceramic X5R

TDK

0402

LMK105BJ474KV-F

Ceramic X5R

Taiyo Yuden

0402

ECJ0EB0J474K

Ceramic X5R

Panasonic

6.3

0402

LEDs

User defined. Note that D7, D8, and D9 outputs are powered from VDD when

specifying the LEDs.

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