10

LM2750, LM2750-ADJ

SNVS180N – APRIL 2002 – REVISED APRIL 2016

www.ti.com

Product Folder Links: LM2750 LM2750-ADJ

Submit Documentation Feedback

Copyright © 2002–2016, Texas Instruments Incorporated

Feature Description (continued)

7.3.2 Input, Output, and Ground Connections

Making good input, output, and ground connections is essential to achieve optimal LM2750 performance. The

two input pads, pads 8 and 9, must be connected externally. It is strongly recommended that the input capacitor

and straight as possible. To minimize the effect of input noise on LM2750 performance, it is best to bring two

traces out from the LM2750 all the way to the input capacitor pad, so that they are connected at the capacitor

pad. Connecting the two input traces between the input capacitor and the LM2750 input pads could make the

LM2750 more susceptible to noise-related performance degradation. TI also recommends that the input capacitor

be on the same side of the PCB as the LM2750, and that traces remain on this side of the board as well (vias to

traces on other PCB layers are not recommended between the input capacitor and LM2750 input pads).

The two output pads, pads 1 and 2, must also be connected externally. TI recommends that the output capacitor

placed as close to the LM2750 device as possible to minimize PCB trace length between the capacitor and the

device. Due to the pad-layout of the part, it is likely that the trace from one of the flying capacitor pads (C+ or C–)

must be routed to an internal or opposite-side layer using vias. This is acceptable, and it is much more

advantageous to route a flying capacitor trace in this fashion than it is to place input traces on other layers.

The GND pads of the LM2750 are ground connections and must be connected externally. These include pads 3

(LM2750-5.0 only), 5, 6, and the die-attach pad (DAP). Large, low-impedance copper fills and via connections to

an internal ground plane are the preferred way of connecting together the ground pads of the LM2750, the input

capacitor, and the output capacitor, as well as connecting this circuit ground to the system ground of the PCB.

7.3.3 Shutdown

When the voltage on the active-low-logic shutdown pin is low, the LM2750 is in shutdown mode. In shutdown,

the LM2750 draws virtually no supply current. There is a 200-k

Ω pulldown resistor tied between the SD pin and

GND that pulls the SD pin voltage low if the pin is not driven by a voltage source. When pulling the part out of

shutdown, the voltage source connected to the SD pin must be able to drive the current required by the 200-k

Ω

resistor. For voltage management purposes required upon start-up, internal switches connect the output of the

LM2750 to an internal pulldown resistor (1 k

Ω typical) when the part is shut down. Driving the output of the

LM2750 by another supply when the LM2750 is shut down is not recommended, as the pulldown resistor was not

sized to sink continuous current.

7.3.4 Soft Start

The LM2750 employs soft-start circuitry to prevent excessive input inrush currents during start-up. The output

voltage is programmed to rise from 0 V to the nominal output voltage (5 V) in 500 µs (typical). Soft start is

engaged when a part, with input voltage established, is taken out of shutdown mode by pulling the SD pin

voltage high. Soft start also engages when voltage is established simultaneously to the input and SD pins.

7.3.5 Output Current Capability

The LM2750-5.0 provides 120 mA of output current when the input voltage is within 2.9 V to 5.6 V. Using the

LM2750 to drive loads in excess of 120 mA is possible.

NOTE

Understanding relevant application issues is recommended and a thorough analysis of the

application circuit must be performed when using the part outside operating ratings and/or

specifications to ensure satisfactory circuit performance in the application. Special care

must be paid to power dissipation and thermal effects. These parameters can have a

dramatic impact on high-current applications, especially when the input voltage is high.

(see Power Efficiency And Power Dissipation).