ml4854 Fairchild Semiconductor, ml4854 Datasheet - Page 11

• Manufacturer Part Number: ml4854
• Description: Adjustable, Low-current, 2-cell Boost Regulator With Shutdown And Low Battery Detect
• Manufacturer: Fairchild Semiconductor

Application Example:
Using ML4854 as a constant current source to drive four LEDs:
The current through the LEDs is maintained constant within a large input voltage range as shown in the diagram below:
ML4854
components. The PCB layout should be based on some
simple rules to minimize EMI and to ensure good regulation
performances:
1.
2.
3.
4. Place the external networks for LBI and FB close to
REV. 1.0.7 5/6/03
Place the IC, inductor, input and output capacitor as
close together as possible.
Keep the output capacitor as close to the ML4854 as
possible with very short traces to V
Typically it should be within 0.25 inches or 6 mm.
Keep the traces for the power components wide,
typically > 50 mils or 1.25 mm.
ML4854, but as far away as possible from the power
components to prevent voltage transient from coupling
into sensitive nodes.
+
Cin
+
1
2
3
4
ML4854
19.8
19.6
19.4
19.2
18.8
18.6
18.4
18.2
L
+
20
19
18
Cout
OUT
0
8
7
6
5
and GND pins.
ML4854 feeds LED QTLP 600C-EB
1
D1
D2
D3
D4
R
R
R
R
Input Voltage (V)
2
5.
6.
On multilayer boards, use component side copper for
grounding around the IC and connect back to a quiet
ground plane using vias. The ground planes act as
electrostatic shields for some of the RF energy radiated.
The connection of the GND pin of the IC (pin 8) to the
overall grounding system should be directly to the
bottom of the output filter capacitor. A star grounding
system radiating from where the power enters the PCB,
is a recommended practice.
3
L = 10µH
Cin = Cout = 10µF
R = 62 ohm
D1...D4 = QTLP 600C-EB (blue)
4
5
PRODUCT SPECIFICATION
11