LMZ12003EXT datasheet(14/29 Pages) TI

14 / 29 page

LMZ12003EXT

SNVS663H – JUNE 2010 – REVISED AUGUST 2015

www.ti.com

Typical Application (continued)

Table 1. Bill of Materials

REF DES

DESCRIPTION

CASE SIZE

MANUFACTURER

MANUFACTURER P/N

SIMPLE SWITCHER

PFM-7

Texas Instruments

LMZ12003EXTTZ-ADJ

Cin1

1 µF, 50 V, X7R

1206

Taiyo Yuden

UMK316B7105KL-T

Cin2

10 µF, 50 V, X7R

1210

Taiyo Yuden

UMK325BJ106MM-T

CO1

1 µF, 50 V, X7R

1206

Taiyo Yuden

UMK316B7105KL-T

CO2

100 µF, 6.3 V, X7R

1210

Taiyo Yuden

JMK325BJ10CR7MM-T

RFBT

1.37 k

Ω

0603

Vishay Dale

CRCW06031K37FKEA

RFBB

1.07 k

Ω

0603

Vishay Dale

CRCW06031K07FKEA

RON

32.4 k

Ω

0603

Vishay Dale

CRCW060332K4FKEA

RENT

32.4 k

Ω

0603

Vishay Dale

CRCW060332K4FKEA

RENB

11.8 k

Ω

0603

Vishay Dale

CRCW060311k8FKEA

CFF

22 nF, ±10%, X7R, 16 V

0603

TDK

C1608X7R1H223K

CSS

22 nF, ±10%, X7R, 16 V

0603

TDK

C1608X7R1H223K

8.2.2.3 Soft-Start Capacitor Selection

Programmable soft-start permits the regulator to slowly ramp to its steady-state operating point after being

enabled, thereby reducing current inrush from the input supply and slowing the output voltage rise-time to

prevent overshoot.

Upon turnon, after all UVLO conditions have been passed, an internal 8-µA current source begins charging the

external soft-start capacitor. The soft-start time duration to reach steady-state operation is given by the formula:

tSS = VREF × CSS / Iss = 0.8 V × CSS / 8 µA

(3)

This equation can be rearranged as follows:

CSS = tSS × 8 μA / 0.8 V

Use of a 0.022-

μF capacitor results in 2.2-ms soft-start duration. This is recommended as a minimum value.

As the soft-start input exceeds 0.8 V the output of the power stage will be in regulation. The soft-start capacitor

continues charging until it reaches approximately 3.8 V on the SS pin. Voltage levels between 0.8 V and 3.8 V

have no effect on other circuit operation. The following conditions will reset the soft-start capacitor by discharging

the SS input to ground with an internal 200-

μA current sink.

• The enable input being pulled low

• Thermal shutdown condition

• Overcurrent fault

• Internal VCC UVLO (Approx 4-V input to VIN)

8.2.2.4 CO Selection

None of the required CO output capacitance is contained within the module. At a minimum, the output capacitor

must meet the worst case minimum ripple current rating of 0.5 × ILR P-P, as calculated in Equation 14. Beyond

that, additional capacitance will reduce output ripple so long as the ESR is low enough to permit it. A minimum

value of 10

μF is generally required. Experimentation will be required if attempting to operate with a minimum

value. Ceramic capacitors or other low ESR types are recommended. See AN-2024 SNVA422 for more detail.

The following equation provides a good first pass approximation of CO for load transient requirements:

CO ≥ ISTEP × VFB × L × VIN / (4 × VO × (VIN – VO) × VOUT-TRAN)

(4)

Solving:

CO ≥ 3 A × 0.8 V × 6.8 μH × 12 V / (4 × 3.3 V × (12 V – 3.3 V) × 33 mV)

≥ 52μF

The LMZ12003EXT demonstration and evaluation boards are populated with a 100-µF 6.3-V X5R output

capacitor. Locations for extra output capacitors are provided.

Submit Documentation Feedback

Product Folder Links: LMZ12003EXT

LMZ12003EXT bảng dữ liệu(PDF) 14 Page - Texas Instruments

LMZ12003EXT bảng dữ liệu(HTML) 14 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

bảng dữ liệu tải về

Link URL