TPS61196
SLVSBG1C –OCTOBER 2012–REVISED FEBRUARY 2013
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UVLO
VIN
EN
PWM
Dimming
10uA
Charging
Current
200uA
Charging
Current
Soft Startup Done
VIFB(min)>VIFBV – 200mV
VREF=2V
Dimming Off
(VOUT = VIN – VD)
15ms
200ms
VOUT
Figure 24. Soft Start Waveforms
Unused LED String
If the application requires less than six LED strings, the TPS61196 simply requires connecting the unused IFB
pin to ground through a resistor between 20kΩ and 36 kΩ. Once the TPS61196 is turned on, the TPS61196 uses
a 60µA current source to detect the IFB pin voltage. If the IFB voltage is between 1.0V and 2.5V, the TPS61196
immediately disables this string during startup.
Current Regulation
The six channel current sink regulators can be configured to provide up to 400mA per string. The expected LED
current is programmed by a resistor (R11 in the SIMPLIFIED SCHEMATIC CIRCUIT) at the ISET using
Equation 3.
V
ISET
ILED
=
´KISET
R11
(3)
Where VISET is the ISET pin voltage of 1.229V and KISET is the current multiple of 3992.
To sink the set LED current, the current sink regulator requires a minimum headroom voltage at the IFB pins for
working properly. For example, when the LED current is set to 130mA, the minimum voltage required at the IFB
pin must be higher than 0.35V. For other LED currents, refer to Figure 8 for recommened minimum headroom
voltage required. The TPS61196 regulates the minimum voltage of the IFB pins to the IFBV voltage. The IFBV
voltage is adjustable with an external resistor (R10 in the SIMPLIFIED SCHEMATIC CIRCUIT) at the IFBV pin.
After choosing the minimum IFB voltage, the IFBV voltage must be set to this value and the setting resistance
can be calculated by Equation 4.
R10
V
=
´ 307.3 mV
( )
IFBV
R11
(4)
If a large LED current is set, the headroom voltage is required higher. This leads to more heat on TPS61196. To
maintain the total power dissipation in the range of the package limit, normally all strings can not sink large
current in continuous mode but pulse mode. The backlight of an active shutter glass 3D TV may work with large
LED current in pulse mode.
14
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