LTC3210-1_15 Datasheet, PDF (9/16 Pages) Linear Technology – MAIN/CAM LED Controller with 64-Step Brightness Control in 3mm 3mm QFN

LTC3210-1
Operation
LED Current Control
The MLED currents are delivered by the four programmable
current sources. 64 linear current settings (0mA to 20mA,
RM = 30.1k) are available by strobing the ENM pin. Each
positive strobe edge decrements a 6-bit down counter
which controls a 6-bit linear DAC. When the desired cur-
rent 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)) • 535
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.
Soft-Start
Initially, when the part is in shutdown, a weak switch
connects V_BAT to CPO. This allows V_BAT to slowly charge
the CPO output capacitor to prevent large charging
currents.
The LTC3210-1 also employs a soft-start feature on its
charge pump to prevent excessive inrush current and
supply droop when switching into the step-up modes.
The current available to the CPO pin is increased linearly
over a typical period of 150µs. Soft-start occurs at the
start of both 1.5x and 2x mode changes.
Charge Pump Strength and Regulation
Regulation is achieved by sensing the voltage at the CPO
pin and modulating the charge pump strength based on
the error signal. The CPO regulation voltages are set in-
ternally, and are dependent on the charge pump modes,
as shown in Table 1.
Table 1. Charge Pump Output Regulation Voltages
CHARGE PUMP MODE
REGULATED V_CPO
1.5x
4.55V
2x
5.05V
ENM
OR ENC
LED
CURRENT
tPW ≥ _200ns
tEN _{150µs (TYP)}
tSD _{150µs (TYP)}
PROGRAMMED
CURRENT
SHUTDOWN
Figure 1. Current Programming Timing Diagram
ENM = ENC = LOW
32101 F01
32101fd