mic3172 Micrel Semiconductor, mic3172 Datasheet - Page 16

• Manufacturer Part Number: mic3172
• Description: 100khz 1.25a Switching Regulators
• Manufacturer: Micrel Semiconductor

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.
M9999-042205
Shutdown (Off)
Enable (On)
4.5V to 20V
V
IN
Figure 15. LCD Backlight Fluorescent Lamp Supply
EN
P1 P2 S
GND
MIC3172
V
IN
COMP
V
FB
SW
R1
C1
L1: Coiltronics CTX300-4P
T1: Coiltronics CTX110602
C2: Polyfilm, WIMA FKP2 0.1µF to 0.68µF
C4: 15pF to 30pF, 3kV min.
D1
300µH
R2
L1
16
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.
Coiltronics, Inc., tel: [phone].
Q1
Q2
C2
C3
Suitable inductors may be obtained from
T1
C4
Cold Cathode
Fluorescent
1N4148
Lamp
C5
D2
R3
R4
D3
1N4148
R5
Intensity
Control
Micrel, Inc.
April 2005