MIC2172_05 Datasheet, PDF (16/17 Pages) Micrel Semiconductor – 100kHz 1.25A Switching Regulators

MIC2172/3172
On/Off Control
Especially important for battery powered applications, the
lamp can be remotely or automatically turned off using the
MIC3172’s EN pin. The entire circuit draws less than 1µA
while shutdown.
Micrel, Inc.
Efficiency
To obtain maximum circuit efficiency careful selection of Q1
and Q2 for low collector to emitter saturation voltage is a
must. Inductor L1 should be chosen for minimal core and
copper losses at the switching frequency of the MIC3172, and
T1 should be carefully constructed from magnetic materials
optimized for the output power required at the Royer oscillator
frequency. Suitable inductors may be obtained from
Coiltronics, Inc., tel: [phone].
V_IN
4.5V to 20V
Enable (On)
Shutdown (Off)
V_IN
EN
V_SW
MIC3172
GND
FB
P1 P2 S COMP
R1
C1
R2
D1
L1
300µH
Q1
C2
C3
Q2
T1
Cold Cathode
Fluorescent
Lamp
C4
D2
1N4148
R3
C5
L1: Coiltronics CTX300-4P
T1: Coiltronics CTX110602
C2: Polyfilm, WIMA FKP2 0.1µF to 0.68µF
C4: 15pF to 30pF, 3kV min.
D3
1N4148
R4
R5
Intensity
Control
Figure 15. LCD Backlight Fluorescent Lamp Supply
M9999-042205
16
April 2005