LTC3210 Datasheet, PDF (9/16 Pages) Linear Technology – MAIN/CAM LED Controller in 3mm × 3mm QFN

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OPERATIO
Power Management
The LTC3210 uses a switched capacitor charge pump to
boost CPO to as much as 2 times the input voltage up to
5.1V. The part starts up in 1x mode. In this mode, V_BAT is
connected directly to CPO. This mode provides maximum
efficiency and minimum noise. The LTC3210 will remain in
1x mode until an LED current source drops out. Dropout
occurs when a current source voltage becomes too low
for the programmed current to be supplied. When dropout
is detected, the LTC3210 will switch into 1.5x mode. The
CPO voltage will then start to increase and will attempt
to reach 1.5x V_BAT up to 4.6V. Any subsequent dropout
will cause the part to enter the 2x mode. The CPO voltage
will attempt to reach 2x V_BAT up to 5.1V. The part will be
reset to 1x mode whenever the part is shut down or when
ENC goes low.
A two phase nonoverlapping clock activates the charge
pump switches. In the 2x mode the flying capacitors are
charged on alternate clock phases from V_BAT to minimize
input current ripple and CPO voltage ripple. In 1.5x mode the
flying capacitors are charged in series during the first clock
phase and stacked in parallel on V_BAT during the second
phase. This sequence of charging and discharging the flying
capacitors continues at a constant frequency of 800kHz.
LED Current Control
The MLED currents are delivered by the four programmable
current sources. Eight current settings (0mA to 20mA,
RM = 30.1k) are available by strobing the ENM pin. Each
positive strobe edge decrements a 3-bit down counter
which controls an exponential DAC. When the desired
LTC3210
current is achieved ENM is stopped high. The output cur-
rent then changes to the programmed value after 150µs
(typ). The counter will stop when the LSB is reached. The
output current is set to 0 when ENM is toggled low after
the output has been enabled. If strobing is started within
150µs (typ), after ENM has been set low, the counter will
continue to count down. After 150µs (typ) the counter
is reset.
The CLED current is delivered by a programmable current
source. Eight linear current settings (0mA to 380mA, RC
= 24.3k) are available by strobing the ENC pin. Each posi-
tive strobe edge decrements a 3-bit down counter which
controls a 3-bit linear DAC. When the desired current is
reached, ENC is stopped high. The output current then
changes to the programmed value after 150µs (typ). The
counter will stop when the LSB is reached. The output
current is set to 0 when ENC is toggled low after the output
has been enabled. If strobing is started within 150µs (typ)
after ENC has been set low, the counter will continue to
count down. After 150µs (typ) the counter is reset.
The full-scale output current is calculated as follows:
MLED full-scale output current
= (1.215V/(RM + 500)) • 515
CLED full-scale output current
= (1.215V/(RC + 500)) • 7500
When both ENM and ENC are held low for 150µs (typ)
the part will go into shutdown. See Figure 1 for timing
information.
ENC resets the mode to 1x on a falling edge.
ENM
OR ENC
LED
CURRENT
tPW ≥ _60ns
tEN _{150µs (TYP)}
tSD _{150µs (TYP)}
PROGRAMMED
CURRENT
SHUTDOWN
ENM = ENC = LOW
3210 F01
Figure 1. Current Programming and Shutdown Timing Diagram
3210f
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