LM2795

SD

Shutdown

Control

*Only on

LM2795

10PA

*

LM2794, LM2795

SNVS168L – JANUARY 2002 – REVISED MAY 2013

www.ti.com

APPLICATION INFORMATION

CIRCUIT DESCRIPTION

The LM2794/5 is a 1.5x/1x CMOS charge pump with four matched constant current outputs, each capable of

driving up to 20mA through White LEDs. This device operates over the extended Li-Ion battery range from 2.7V

to 5.5V. The LM2794/5 has four regulated current sources connected to the device's 1.5x charge pump output

or above 4.7V (typ.). The device can drive up to 80mA through any combination of LEDs connected to the

reference current is then multiplied and mirrored to each constant current output. The LED brightness can then

be controlled by analog and/or digital methods. Applying an analog voltage in the range of 0V to 3.0V to the

Brightness pin (BRGT) adjusts the dimming profile of the LEDs. The digital technique uses a PWM (Pulse Width

Modulation) signal applied to the Shutdown pin (SD). (see ISET AND BRGT PINS).

SOFT START

Soft start is implemented internally by ramping the reference voltage more slowly than the applied voltage.

During soft start, the current through the LED outputs will ramp up in proportion to the rate that the reference

voltage is being ramped up.

SHUTDOWN MODE

The shutdown pin (SD) disables the part and reduces the quiescent current to 2.3µA (typ.).

The LM2795 has an active-high shutdown pin (HIGH = shutdown, LOW = operating). An internal pull-up is

shutdown, as shown in Figure 22. The LM2795 SD pin can also be driven with a rail-to-rail CMOS logic signal.

Figure 22. 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.

10

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