Texas Instruments TPS61181(82/81A)-259 Evaluation Board TPS61181(82/81A)EVM-259 TPS61181AEVM-259 TPS61181AEVM-259 Hoja De Datos
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TPS61181AEVM-259
SLVSAN6A
–
FEBRUARY 2011
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REVISED MARCH 2011
If one of the WLED strings is open, the boost output rises to over-voltage threshold (39V typical). The
TPS61181A detects the open WLED string by sensing no current in the corresponding IFB pin. As a result, the
IC removes the open IFB pin from the voltage feedback loop. Subsequently, the output voltage drops down and
is regulated to a voltage for the connected WLED strings. The IFB current of the connected WLED strings keep
in regulation during the whole transition. The IC only shuts down if it detects that all of the WLED strings are
open.
TPS61181A detects the open WLED string by sensing no current in the corresponding IFB pin. As a result, the
IC removes the open IFB pin from the voltage feedback loop. Subsequently, the output voltage drops down and
is regulated to a voltage for the connected WLED strings. The IFB current of the connected WLED strings keep
in regulation during the whole transition. The IC only shuts down if it detects that all of the WLED strings are
open.
If the over-voltage threshold is reached, but the current sensed on the IFB pin is below the regulation target, the
IC regulates the boost output at the over-voltage threshold. This operation could occur when the WLED is turned
on under cold temperature, and the forward voltages of the WLEDs exceed the over-voltage threshold.
Maintaining the WLED current allows the WLED to warm up and their forward voltages to drop below the
over-voltage threshold.
IC regulates the boost output at the over-voltage threshold. This operation could occur when the WLED is turned
on under cold temperature, and the forward voltages of the WLEDs exceed the over-voltage threshold.
Maintaining the WLED current allows the WLED to warm up and their forward voltages to drop below the
over-voltage threshold.
If any IFB pin voltage exceeds IFB over-voltage threshold (17V typical), the IC turns off the corresponding current
sink and removes this IFB pin from V
sink and removes this IFB pin from V
O
regulation loop. The remaining IFB pins
’
current regulation is not affected.
This condition often occurs when there are several shorted WLEDs in one string. WLED mismatch typically does
not create such large voltage difference among WLED strings.
not create such large voltage difference among WLED strings.
IFB PIN UNUSED
If the application requires less than 6 WLED strings, one can easily disable unused IFB pins. The TPS61181A
simply requires leaving the unused IFB pin open or shorting it to ground. If the IFB pin is open, the boost output
voltage ramps up to V
simply requires leaving the unused IFB pin open or shorting it to ground. If the IFB pin is open, the boost output
voltage ramps up to V
O
over-voltage threshold during start up. The IC then detects the zero current string, and
removes it from the feedback loop. If the IFB pin is shorted to ground, the IC detects the short immediately after
IC enable, and the boost output voltage does not go up to V
IC enable, and the boost output voltage does not go up to V
O
over-voltage threshold. Instead, it ramps to the
regulation voltage after soft start.
Copyright
©
2011, Texas Instruments Incorporated
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