Texas Instruments TPS61181(82/81A)-259 Evaluation Board TPS61181(82/81A)EVM-259 TPS61181EVM-259 TPS61181EVM-259 Datenbogen
Produktcode
TPS61181EVM-259
SLVS801E – DECEMBER 2007 – REVISED APRIL 2013
For the TPS61181/2 ICs, if one of the WLED strings is open, the boost output rises to over-voltage threshold
(39V typical). The IC 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
string keeps in regulation during the whole transition. The IC only shuts down if it detects that all of the WLED
strings are open.
(39V typical). The IC 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
string keeps in regulation during the whole transition. The IC only shuts down if it detects that all of the WLED
strings are open.
For the TPS61180, if the IC detects any open WLED string, the IC shuts down and remains off until there is V
BAT
POR or EN pin toggling.
For all the devices, 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.
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.
For the TPS61181/2 ICs, 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
the corresponding current 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.
WLED mismatch typically does not create such large voltage difference among WLED strings.
For the TPS61180 IC, if any IFB pin voltage exceeds IFB over-voltage threshold, the IC shuts down and remains
off until there is V
off until there is V
BAT
POR or EN pin toggling.
IFB PIN UNUSED
If the application requires less than 6 WLED strings, one can easily disable unused IFB pins. The TPS61181/2
ICs simply require 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
ICs simply require 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
after 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.
For the TPS61180, connect a 10 k
Ω
resistor from the unused IFB pin to ground. After the device is enabled, the
IC detects the resistor and disables the IFB pin from the feedback loop.
Copyright © 2007–2013, Texas Instruments Incorporated
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