Datasheet

ManualsBrandsTEXAS INSTRUMENTS ManualsPMICsPMIC - LDO voltage regulator Positive, fixed DSBGA 4

DC/DC

GND

OUT

LM3673TL-

1.8

10 PF

4.7 PF

2.2 PH

LP3991TL-

1.5

LDO

GND

4.7 PF

Li-Ion

2.7 ± 4.3V

1.5V

Ferrite

Bead

1.8V

LP3991

www.ti.com

SNVS296H –DECEMBER 2006–REVISED MAY 2013

DSBGA MOUNTING

The DSBGA package requires specific mounting techniques which are detailed in the Texas Instruments

Application Note (AN-1112). Referring to the section Surface Mount Technology (SMT) Assenbly Considerations,

it should be noted that the pad style which must be used with the 4 pin package is NSMD (non-solder mask

defined) type.

For best results during assembly, alignment ordinals on the PCB may be used to facilitate placement of the

DSBGA device.

DSBGA LIGHT SENSITIVITY

Exposing the DSBGA device to direct sunlight may cause mis-operation of the device. Light sources such as

halogen lamps can affect the electrical performance if brought near to the device.

The wavelengths which have most detrimental effect are reds and infra-reds, which means that fluorescent

lighting, used inside most buildings will have little effect on performance.

Figure 18. LP3991 Used as a Post DC/DC regulator

POST-BUCK REGULATOR

Linear Post-Regulation can be an effective way to reduce ripple and switching noise from DC/DC convertors

while still maintaining a reasonably high overall efficiency.

The LP3991 is particularly suitable for this role due to its low input voltage requirements. In addition, there is

often no need for a separate input capacitor for the LP3991 as it can share the output cap of the DC/DC

convertor.

Care of PCB layouts involving switching regulators is paramount. In particular, the ground paths for the LDO

should be routed separately from the switcher ground and star connected close to the battery. Routing of the

switch pin of the DC/DC convertor must be kept short to minimize radiated EMI. A low pass filter such as a ferrite

bead or common mode choke on the battery input leads can further reduce radiated EMI.

Figure 18 shows a typical example using an LM3673, 350mA DC/DC buck regulator with a nominal output of

1.8V and a 1.5V LP3991. The overall efficiency will be greater than 70% over the full Li-Ion battery voltage

range. Maximum efficiency is achieved by minimizing the difference between V

and V

OUT

of the LP3991. The

LP3991-1.5 will remain in regulation down to an input voltage of 1.65V, so, in this case, a 1.8V buck with 5%

tolerance is adequate for all conditions of temperature and load.

Product Folder Links: LP3991