UCC3954 Datasheet, PDF (1/10 Pages) Texas Instruments – Single Cell Lithium-Ion to +3.3V Converter

UCC3954
PRELIMINARY INFORMATION
Single Cell Lithium-Ion to +3.3V Converter
FEATURES
• Converts Lithium-Ion Cell to
+3.3V at 700mA Load
Current
• Load Disconnect in
Shutdown
• High Efficiency Flyback
Operation
• Internal 0.15Ω Switch
• Low Battery LED Driver
• Internal 2A Current Limit
• Internal 200kHz Oscillator
• 8 Pin D, N, 14 Pin PW
Packages
DESCRIPTION
The UCC3954, along with a few external components, develops a regulated +3.3V
from a single lithium-ion battery whose terminal voltage can vary between 2.5V and
4.2V. The UCC3954 employs a simple flyback (Buck-Boost) technique to convert the
battery energy to +3.3V. This is accomplished by referencing the lithium-ion cell’s
positive terminal to system ground. The negative terminal of the battery is the return
point for the UCC3954. This approach enables the converter to maintain constant fre-
quency operation whether the cell voltage is above or below the output voltage. An
additional benefit of this technique is its inherent ability to disconnect the battery from
the load in shutdown mode.
The UCC3954 operates as a fixed 200kHz switching frequency voltage mode flyback
converter. The oscillator time base and ramp are internally generated by the
UCC3954 and require no external components. A 2A current limit for the internal
0.15Ω power switch provides protection in the case of an output short circuit. When
left open, an internal 100kΩ resistor pulls the SD pin to BAT–, which puts the
UCC3954 in shutdown mode, and thereby reduces power consumption to sub-µA lev-
els. A low battery detect function will drive the LOWBAT pin low (minimum of 5mA
sink current) when the battery has been discharged to within 200mV of the prede-
fined lockout voltage. The LOWBAT pin is intended for use with an external LED to
provide visual warning that the battery is nearly exhausted. The lockout mode is acti-
vated when the battery is discharged to 2.55V. In lockout mode, the part consumes
15µA. Once the UCC3954 has entered lockout mode, the user must insert a fresh
battery whose open circuit voltage is greater than 3.1V. This prevents a system-level
oscillation of the lockout function due to the lithium-ion battery’s large equivalent se-
ries resistance.
Additional features of the UCC3954 include a trimmed –1.1V reference and internal
feedback scaling resistors, a precision error amplifier, low quiescent current drain in
shutdown mode, and a softstart function. The UCC3954 is offered in the 8 pin D,
14 pin PW (surface mount), and N (through hole) packages.
BLOCK DIAGRAM
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UDG-96137-1