ltc3210 Linear Technology Corporation, ltc3210 Datasheet - Page 9

• Manufacturer Part Number: ltc3210
• Description: Main/cam Led Controller In 3mm ? 3mm Qfn
• Manufacturer: Linear Technology Corporation

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
connected directly to CPO. This mode provides maximum
effi ciency 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
will cause the part to enter the 2x mode. The CPO voltage
will attempt to reach 2x V
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 fl ying capacitors are
charged on alternate clock phases from V
input current ripple and CPO voltage ripple. In 1.5x mode the
fl ying capacitors are charged in series during the fi rst clock
phase and stacked in parallel on V
phase. This sequence of charging and discharging the fl ying
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
SHUTDOWN
CURRENT
OR ENC
BAT
U
ENM
LED
up to 4.6V. Any subsequent dropout
BAT
up to 5.1V. The part will be
t PW ≥ 60ns
Figure 1. Current Programming and Shutdown Timing Diagram
BAT
during the second
BAT
to minimize
BAT
is
t EN 150μs (TYP)
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:
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.
MLED full-scale output current
=
CLED full-scale output current
=
(
(
1.215V/(RM + 500)
1.215V/(RC + 500)
PROGRAMMED
CURRENT
t SD 150μs (TYP)
)
)
• 7500
• 515
ENM = ENC = LOW
3210 F01
LTC3210
3210fa
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