LM2795

SD

Shutdown

Control

*Only on

LM2795

10PA

*

LM2794, LM2795

www.ti.com

SNVS168K – MAY 2004 – REVISED MAY 2004

Figure 2. Open-Drain Logic Shutdown Control

The LM2794 has an active-low shutdown pin (LOW = shutdown, HIGH = operating). The LM2794 SD pin can be

driven with a low-voltage CMOS logic signal (1.5V logic, 1.8V logic, etc). There is no internal pull-up or pull-down

on the SD pin of the LM2794.

CAPACITOR SELECTION

The LM2794/5 requires 4 external capacitors for proper operation. Surface-mount multi-layer ceramic capacitors

are recommended. These capacitors are small, inexpensive and have very low equivalent series resistance

(ESR,

≤15mΩ typ.). Tantalum capacitors, OS-CON capacitors, and aluminum electrolytic capacitors are generally

not recommended for use with the LM2794/5 due to their high ESR, as compared to ceramic capacitors.

For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with

the LM2794/5. These capacitors have tight capacitance tolerance (as good as ±10%), hold their value over

temperature (X7R: ±15% over

−55°C to 125°C; X5R: ±15% over −55°C to 85°C), and typically have little voltage

coefficient. Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with

the LM2794/5. Capacitors with these temperature characteristics typically have wide capacitance tolerance

(+80%,

−20%), vary significantly over temperature (Y5V: +22%, −82% over −30°C to +85°C range; Z5U: +22%,

−56% over +10°C to +85°C range), and have poor voltage coefficients. Under some conditions, a nominal 1µF

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

and Z5U capacitors to fail to meet the minimum capacitance requirements of the LM2794/5. Table 1 lists

suggested capacitor suppliers for the typical application circuit.

Table 1. Ceramic Capacitor Manufacturers

Manufacturer

Contact

TDK

www.component.tdk.com

Murata

www.murata.com

Taiyo Yuden

www.t-yuden.com

LED SELECTION

The LM2794/5 is designed to drive LEDs with a forward voltage of about 3.0V to 4.0V. The typical and maximum

diode forward voltage depends highly on the manufacturer and their technology. Table 2 lists two suggested

manufacturers. Forward current matching is assured over the LED process variations due to the constant current

output of the LM2794/5.

Table 2. White LED Selection

Manufacturer

Contact

Osram

www.osram-os.com

Nichia

www.nichia.com

The current mirror circuitry matches the current through each LED to within 0.5%.

Copyright © 2004, Texas Instruments Incorporated

Submit Documentation Feedback

9

Product Folder Links: LM2794 LM2795