MIC2292-34YML TR Micrel Inc, MIC2292-34YML TR Datasheet - Page 8

• Manufacturer Part Number: MIC2292-34YML TR
• Description: IC LED DRIVER WHITE BCKLGT 8-MLF
• Manufacturer: Micrel Inc
• Type: Backlight, White LEDr

Specifications of MIC2292-34YML TR

• Constant Current: Yes
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: White LED
• Frequency: 1.4MHz ~ 1.8MHz
• 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
• Operating Supply Voltage (typ): 3.3/5/9V
• Number Of Segments: 3
• Operating Temperature (min): -40C
• Operating Temperature (max): 125C
• Operating Temperature Classification: Automotive
• Package Type: MLF
• Pin Count: 8
• Mounting: Surface Mount
• Operating Supply Voltage (min): 2.5V
• Operating Supply Voltage (max): 10V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Efficiency: -
• Lead Free Status / Rohs Status: Compliant
• Other names: 576-1735-2; MIC2292-34YMLTR; MIC2292-34YMLTR

Dimming Control
There are two techniques for dimming control. One is PWM
dimming and the other is continuous dimming.
September 2009
MIC2292/93
1. PWM dimming control is implemented by applying
2. Continuous dimming control is implemented by
a PWM signal on EN pin as shown in Figure 1.
The MIC2292/93 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
MIC2292/93 through a series resistor as shown in
Figure 2. The LED current is decreased proportion-
ally 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 volt-
age 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.
V
IN
V
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
8
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 MIC2292/93 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 MIC2292/93 has
two product options in the 8-lead MLF
protection, OVP. The extra pins of the 8-leadMLF
allow the use of a dedicated OVP monitor with options for 15V
or 34V (see Figure 3). The reason for the two OVP levels
is to let users choose the suitable level of OVP for their ap-
plication. For example, a 4-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, and accordingly, 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, C
drive to the FB pin at start-up, resulting in gradual increase
of switch duty cycle and limited inrush current.
V
IN
Figure 3. MLF
V
IN
Figure 4. Soft-Start Circuit
VIN
EN
GND
OUT
®
SW
VIN
EN
FB
Package OVP Circuit
GND
OUT
SW
FB
C
SS
R
2200pF
10k
®
ss
with overvoltage
, provides over-
M9999-091509
Micrel, Inc.
®
package