LTC3210-2/LTC3210-3
9
321023fb
operaTion
Power Management
The LTC3210-2/LTC3210-3 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
LTC3210-2/LTC3210-3 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
LTC3210-2/LTC3210-3 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 program-
mable current
sources. 32 linear current settings (0mA
to 20mA, RM = 30.1k) are available by strobing the ENM
pin. Each positive strobe edge decrements a 5-bit down
Figure 1. Current Programming Timing Diagram
counter which controls a 5-bit linear DAC. When the
desired current is achieved ENM 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 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)) • 525
CLED full-scale output current
=
(1.215V/(RC + 500)) • 7700
When both ENM and ENC are held low for more than
150µs (typ) the part will go into shutdown. See Figure 1
for timing information.
ENC resets the mode to 1x on a falling edge.
t
PW
≥
200ns
ENM = ENC = LOW
SHUTDOWN
t
EN 150µs (TYP)
t
SD 150µs (TYP)
PROGRAMMED
CURRENT
ENM
OR ENC
LED
CURRENT
321023 F01
