MIC2289-34YML TR Micrel Inc, MIC2289-34YML TR Datasheet - Page 7

• Manufacturer Part Number: MIC2289-34YML TR
• Description: IC LED DRIVER WHITE BCKLGT 8-MLF
• Manufacturer: Micrel Inc
• Type: Backlight, White LEDr

Specifications of MIC2289-34YML TR

• Constant Current: Yes
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Backlight, Flash/Torch
• Type - Secondary: White LED
• Frequency: 1.05MHz ~ 1.35MHz
• Voltage - Supply: 2.5 V ~ 10 V
• Mounting Type: Surface Mount
• Package / Case: 8-MLF®, QFN
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 20mA
• Internal Switch(s): Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Efficiency: -
• Other names: 576-1732-2; MIC2289-34YMLTR; MIC2289-34YMLTR

Dimming Control
There are two techniques for dimming control. One is
PWM dimming, and the other is continuous dimming.
Micrel, Inc.
July 2007
1. PWM dimming control is implemented by
2. Continuous dimming control is implemented by
V
IN
V
applying a PWM signal on EN pin as shown in
Figure 1. The MIC2289 is turned on and off by
the PWM signal. With this method, the LEDs
operate with either zero or full current. The
average LED current is increased proportionally
to the duty-cycle of the PWM signal. This
technique has high-efficiency because the IC
and the LEDs consume no current during the off
cycle of the PWM signal. Typical frequency
should be between 100Hz and 10kHz.
applying a DC control voltage to the FB pin of
the MIC2289 through a series resistor as shown
in Figure 2. The LED current is decreased
proportionally with the amplitude of the control
voltage. The LED intensity (current) can be
dynamically varied applying a DC voltage to the
FB pin. The DC voltage can come from a DAC
signal, or a filtered PWM signal. The advantage
of this approach is that a high frequency PWM
signal (>10kHz) can be used to control LED
intensity.
IN
Figure 1. PWM Dimming Method
Figure 2. Continuous Dimming
PWM
VIN
EN
VIN
EN
GND
OUT
GND
SW
FB
Equivalent
OUT
SW
FB
DC
49.9k
5.11k
7
Open-Circuit Protection
If the LEDs are disconnected from the circuit, or in case
an LED fails open, the sense resistor will pull the FB pin
to ground. This will cause the MIC2289 to switch with a
high duty-cycle, resulting in output overvoltage. This may
cause the SW pin voltage to exceed its maximum
voltage rating, possibly damaging the IC and the
external components. To ensure the highest level of
protection, the MIC2289 has 3 product options in the
2mm × 2mm MLF
The extra pins of the 2mm × 2mm MLF
allow a dedicated OVP monitor with options for 15V,
24V, or 34V (see Figure 3). The reason for the three
OVP levels is to let users choose the suitable level of
OVP for their application. For example, a 3-LED
application would typically see an output voltage of no
more than 12V, so a 15V OVP option would offer a
suitable level of protection. This allows the user to select
the output diode and capacitor with the lowest voltage
ratings, therefore smallest size and lowest cost. The
OVP will clamp the output voltage to within the specified
limits.
Start-Up and Inrush Current
During start-up, inrush current of approximately double
the nominal current flows to set up the inductor current
and the voltage on the output capacitor. If the inrush
current needs to be limited, a soft-start circuit similar to
Figure 4 could be implemented. The soft-start capacitor,
CSS, provides over-drive to the FB pin at start-up,
resulting in gradual increase of switch duty cycle and
limited inrush current.
V
IN
V
IN
Figure 4. One of Soft-Start Circuit
VIN
EN
Figure 3. OVP Circuit
®
-8 with overvoltage protection, OVP.
GND
OUT
SW
VIN
EN
FB
GND
OUT
SW
FB
C
SS
R
2200pF
10k
M9999-071007
®
-8 package
MIC2289