TPS61176 Datasheet, PDF (15/28 Pages) Texas Instruments – High-Efficiency 6-Channel WLED Driver Supporting Single-Cell Li-Ion Battery Input

TPS61176
www.ti.com
SLVSBM5 – DECEMBER 2012
V_OUT
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R_upper
R_down
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+ 1_÷÷ø ´ V_{OVP _ clamp}
(4)
Where: V_{OVP_clamp} = 1.5 V
When the over-voltage threshold V_{OVP_clamp} is reached, TPS61176 detects if there is any LED string open first by
sensing whether there is current on IFBx pin. If any string is open, the corresponding current sink is disabled and
removed from regulation. Subsequently, the output voltage drops down and will be regulated to a voltage for the
connected WLED strings. The IFBx current of the connected WLED strings keeps in regulation during the whole
transition. If an open string is reconnected again, a POR toggling or PWM toggling is required to reactivate a
previously deactivated string. TPS61176 shuts down and keeps off when it detects that all of the WLED strings
are open. In this case, a POR toggling or PWM toggling is required to restart the IC. If there isn’t any string open,
TPS61176 regulates the boost output at the over-voltage threshold.
If the output voltage can’t be regulated at the value set by Equation 4 and keeps rising, once the OVP pin voltage
exceeds V_{OVP_sd} rising threshold (1.6V typical), the boost stops switching. When the OVP voltage falls below
V_{OVP_sd} falling threshold (1.55V typical), the boost recovers to switch. During the process, the IFBx current of the
connected WLED strings keeps in regulation.
CURRENT SINK OPEN PROTECTION
If any IFBx pin voltage is detected to exceed the 1st level IFB over-voltage threshold (8.5V typical) when its
current sink is turned on, TPS61176 turns off this current sink and removes it from output regulation loop. The
current regulation of the remaining IFBx pins is not affected. This situation often occurs when there are several
shorted WLED diodes in one string. WLED mismatch typically does not create such large voltage difference
among WLED strings. TPS61176 shuts down when it detects that all of the IFBx pin voltages exceed the
threshold. In this case, a POR toggling or PWM toggling is required to restart the IC.
If any IFBx pin voltage is detected to exceed the 2nd level IFB over-voltage threshold (18V typical) no matter the
current sink is turned on or off, TPS61176 shuts down immediately to avoid potential over stress damage at IFBx
pin. A POR toggling or PWM toggling is required to restart the IC.
OVER CURRENT AND SHORT CIRCUIT PROTECTION
TPS61176 has a pulse-by-pulse over-current limit of 2.0A (min). The boost power MOSFET is turned off when
the inductor current reaches this current limit threshold and it remains off until the beginning of the next switching
cycle. This protects TPS61176 and external component under overload conditions.
Under severe over-load or short circuit conditions, if the OVP pin voltage is detected below V_{OVP_SC} ramp down
threshold (70mV typical), TPS61176 shuts down and the MODE/FAULT pin is pulled to VIN by an internal switch
immediately. As a result, the external isolation MOSFET can be turned off at once, cutting off the power path
from input to output. The IC restarts after a POR toggling or PWM toggling.
THERMAL PROTECTION
An internal thermal shutdown turns off the device when the typical junction temperature of 160°C is exceeded.
The device is released from shutdown automatically when the junction temperature decreases by 15°C.
Copyright © 2012, Texas Instruments Incorporated
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