LTC3210-2 Datasheet, PDF (11/16 Pages) Linear Technology – MAIN/CAM LED Controllers with 32-Step Brightness Control in 3mm × 3mm QFN

LTC3210-2/LTC3210-3
OPERATION
From Figure 2, for 1.5x mode the available current is
given by:
I_OUT
=
(1.5V_BAT –
R_OL
V_CPO )
For 2x mode, the available current is given by:
I_OUT
=
(2V_BAT – V_CPO)
R_OL
Notice that the advantage voltage in this case is 3.1V • 2
– 3.8V – 0.1V = 2.3V. R_OL is higher in 2x mode but a sig-
nificant overall increase in available current is achieved.
Typical values of R_OL as a function of temperature are
shown in Figure 3 and Figure 4.
Shutdown Current
In shutdown mode all the circuitry is turned off and the
LTC3210-2/LTC3210-3 draw a very low current from the
V_BAT supply. Furthermore, CPO is weakly connected to V_BAT.
The LTC3210-2/LTC3210-3 enter shutdown mode when
both the ENM and ENC pins are brought low at 150μs (typ).
ENM and ENC have 250k internal pull down resistors to de-
fine the shutdown state when the drivers are in a high imped-
ance state.
Thermal Protection
The LTC3210-2/LTC3210-3 have built-in overtemperature
protection. At internal die temperatures of around 150°C
thermal shut down will occur. This will disable all of the
current sources and charge pump until the die has cooled
by about 15°C. This thermal cycling will continue until the
fault has been corrected.
Mode Switching
The LTC3210-2/LTC3210-3 will automatically switch from
1x mode to 1.5x mode and subsequently to 2x mode
whenever a dropout condition is detected at an LED pin.
Dropout occurs when a current source voltage becomes
too low for the programmed current to be supplied. The
time from drop-out detection to mode switching is typi-
cally 0.4ms.
The part is reset back to 1x mode when the part is shut
down (ENM = ENC = Low) or on the falling edge of ENC.
An internal comparator will not allow the main switches to
connect V_BAT and CPO in 1x mode until the voltage at the
CPO pin has decayed to less than or equal to the voltage
at the V_BAT pin.
3.8
V_BAT = 3V
3.6
V_CPO = 4.2V
C2 = C3 = C4 = 2.2μF
3.4
3.2
3.0
2.8
2.6
2.4
–40
–15 10
35
TEMPERATURE (°C)
60
85
321023 F03
Figure 3. Typical 1.5x R_OL vs Temperature
4.6
V_BAT = 3V
4.4
V_CPO = 4.8V
C2 = C3 = C4 = 2.2μF
4.2
4.0
3.8
3.6
3.4
3.2
–40
–15 10
35
60
85
TEMPERATURE (°C)
321023 F04
Figure 4. Typical 2x R_OL vs Temperature
321023fa
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