MIC2845 Datasheet, PDF (11/21 Pages) Micrel Semiconductor – 6 Channel High Side Current Source WLED driver

Micrel Inc.
Functional Diagram
MIC2845/46
Figure 1. MIC2845 and MIC2846 Functional Block Diagram
Functional Description
The MIC2845/6 is a 6 channels WLED driver with dual
150mA LDOs. The WLED driver is designed to maintain
proper current regulation with LED current accuracy of
95% while the minimum matching between the 6
channels to be 96.5% at room temperature. The WLEDs
are driven independently from the input supply and will
maintain regulation with a dropout of 50mV at 20mA.
The low dropout of the current sinks allows the WLEDs
to be driven directly from the input voltage and
eliminates the need for large and inefficient charge
pumps. If desired, multiple channels can be combined to
drive a single WLED at a higher current for an intense
light output. The combined method generates an
extremely bright light suited for camera flash
applications. The maximum WLED current for each
channel is set via an external resistor. If dimming is
desired the MIC2845 can dim via a PWM signal while
the MIC2846 is controlled by a single-wire digital
interface. Both dimming controls will be discussed in
detail in the following sections.
The MIC2845/6 has two LDOs with a dropout voltage of
150mV at 150mA and consume 25µA of current in
operation. Each LDO has a dedicated enable pin, which
can reduce operating current down to 0.01µA in
shutdown. Both linear regulators are stable with just 1µF
of output capacitance.
Block Diagram
As shown in Figure 1, the MIC2845/6 consists of 2 LDOs
and 6 current mirrors set to copy a master current
determined by R_SET. The current sinks have a
designated control block for enabling and dimming of the
WLEDs. The MIC2845 is controlled by the PWM control
block that receives PWM signals for dimming. The
MIC2846 dimming is controlled by an internal Digital
Control Interface. The LDOs each have their own control
block and are independent of the current sinks. In each
LDO block, there are internal feedback resistors, an
error amplifier, a PFET transistor and a control circuit for
enabling.
January 2008
11
M9999-010808-A