FAN5331 Fairchild Semiconductor, FAN5331 Datasheet - Page 8

• Manufacturer Part Number: FAN5331
• Description: The FAN5331 is a general purpose, fixed-frequency boost converter designed to operate at high switching frequencies in order to minimize switching noise measured at the battery terminal of hand-held communications equipment
• Manufacturer: Fairchild Semiconductor

FAN5331 Rev. 1.0.1
The feedback loop tightly regulates the current in the branch
connected to FB pin, while the current in the other branch
depends on the sum of the LED’s forward voltages, V
the ballast resistor. The input and the output ripple is less than
3mV
A Zener diode (V
can prevent the FAN5331 from being damaged by over-voltage,
if the load is accidently disconnected during operation.
2. Dual Boost Converter
A negative voltage can be provided by adding an external
charge pump (C1, C2, D2, and D3).
RMS
V
IN
ON
20.2
20.1
20.0
19.9
19.8
19.7
C
4.7 F
, for load currents up to 40mA.
IN
Figure 7. Dual (±) Boost Converter
OFF
2.7V to 5.5V
2.5
LED Current vs Input Voltage
(String Connected to FB Pin)
5
4
V
SHDN
3.0
Z
IN
= 22V) connected between V
L
3.5
H
GND
Input Voltage (V)
SW
FB
1
3
2
4.0
0.1 F
C1
BAT54
D1
4.5
BAT54S
R1
R2
D3
D2
5.0
C2
4.7 F
120pF
C
F
5.5
OUT
4.7 F
C
I
OUT
OUT
6.0
and GND
= 10mA
V
I
OUT
-V
OUT
OUT
OUT
= 50mA
and
8
While the feedback loop tightly regulates V
put voltage (-V
age. Nevertheless, the negative voltage depends on the
changes of the load current in both -V
in the graph below.
-18
-16
-14
-12
-10
Negative Output Voltage vs Load Current
0
Load Current On Positive Output Side (mA)
OUT
) can supply a light load with a negative volt-
10
-15V/Unloaded
20
-15V/10mA Load
OUT
30
and +V
OUT
, the negative out-
40
www.fairchildsemi.com
OUT
, as shown
50