MIC2846A Datasheet, PDF (11/19 Pages) Micrel Semiconductor – High Efficiency 6 Channel Linear WLED Driver with DAM™, Digital Control and Dual Low IQ LDOs

Micrel Inc.
VIN
The input supply (VIN) provides power to the LDOs, the
linear LED drivers and the control circuitry. The V_IN
operating range is 3V to 5.5V. A minimum bypass
capacitor of 1µF should be placed close to the input
(VIN) pin and the ground (GND) pin. Refer to the layout
recommendations section for details on placing the input
capacitor (C1).
LDO1/LDO2
The output pins for LDO one and LDO two are labeled
LDO1 and LDO2, respectively. A minimum of 1µF
bypass capacitor should be placed as close as possible
to the output pin of each LDO. Refer to the layout
recommendations section for details on placing the
output capacitor (C2, C3) of the LDOs.
EN1/EN2
A logic high signal on the enable pin activates the LDO
output voltage of the device. A logic low signal on the
enable pin deactivates the output and reduces supply
current to less than 1µA. EN1 controls LDO1 and EN2
controls LDO2. Do not leave these control pins floating.
DC
The DC pin is used to enable and control dimming of the
linear drivers on the MIC2846A. See the MIC2846A
Digital Dimming Interface in the Application Information
section for details. Pulling the DC pin low for more than
1260μs puts the MIC2846A into a low I_Q sleep mode.
The DC pin cannot be left floating; a floating enable pin may
cause an indeterminate state on the outputs. A 200kΩ pull
down resistor is recommended.
R_SET
The R_SET pin is used by connecting a R_SET resistor to
ground to set the peak current of the linear LED
driver. The average LED current can be calculated
by the equation (1).
I_LED (mA) = 410 * ADC / R_SET (kΩ)
(1)
ADC is the average duty cycle of the LED current
controlled by the single-wire digital dimming. See Table
1 for ADC values. When the device is fully on the
average duty cycle equals 100% (ADC=1). A plot of I_LED
versus R_SET at 100% duty cycle is shown in Figure 2.
MIC2846A
Figure 2. Peak LED Current vs. R_SET (100% Duty Cycle)
D1-D6
The D1 through D6 pins are the LED driver for LED 1
through 6, respectively. The anodes of the LEDs are
connected to VIN and the cathodes of the LEDs are
connected to D1 through D6. When operating with less
than six LEDs, leave the unused D pins unconnected.
The six LED channels are independent of one another
and may be combined or used separately. During start-
up, the D1 through D6 channels are turned on in
synchronization at around 250µs apart.
GND
The ground pin is the ground path for the linear drivers
and LDOs. The ground of the input capacitor should be
routed with low impedance traces to the GND pin and
made as short as possible. Refer to the layout
recommendations for more details.
April 2010
11
M9999-041210-D