MIC2291-34YML TR Micrel Inc, MIC2291-34YML TR Datasheet - Page 6

• Manufacturer Part Number: MIC2291-34YML TR
• Description: IC LED DRIVER PHOTO FLASH 8-MLF
• Manufacturer: Micrel Inc
• Type: Photo Flash LEDr

Specifications of MIC2291-34YML TR

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: 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: 100mA
• Internal Switch(s): Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Efficiency: -
• Other names: 576-1734-2; MIC2291-34YMLTR; MIC2291-34YMLTR

Functional Diagram
Functional Description
The MIC2291 is a constant frequency, PWM current
mode boost regulator. The block diagram is shown
above. The MIC2291 is composed of an oscillator, slope
compensation ramp generator, current amplifier, g
amplifier, PWM generator, and a 500mA bipolar output
transistor. The oscillator generates a 1.2MHz clock. The
clock’s two functions are to trigger the PWM generator
that turns on the output transistor and to reset the slope
compensation ramp generator. The current amplifier is
used to measure the switch cur-rent by amplifying the
voltage signal from the internal sense resistor. The
output of the current amplifier is summed with the output
of the slope compensation ramp generator. This
summed current-loop signal is fed to one of the inputs of
the PWM generator.
Micrel, Inc.
May 2007
*
OVP available on MLF
V
VIN
REF
95mV
FB
OVP*
OVP*
g
®
m
package option only
Figure 1. MIC2291 Block Diagram
Oscillator
1.2MHz
m
error
6
Generator
Generator
The g
the external sense resistor and amplifies the error
between the detected signal and the 95mV reference
voltage. The output of the gm error amplifier provides the
voltage-loop signal that is fed to the other input of the
PWM generator. When the current-loop signal exceeds
the voltage-loop signal, the PWM generator turns off the
bipolar output transistor. The next clock period initiates
the next switching cycle, maintaining the constant
frequency current-mode PWM control. The LED is set by
the feedback resistor:
The Enable pin shuts down the output switching and
disables control circuitry to reduce input current-to-
leakage levels. Enable pin input current is zero at zero
volts.
Ramp
PWM
EN
m
error amplifier measures the LED current through
I
LED
=
95mW
R
FB
SW
GND
M9999-051507
MIC2291