FAN4860 Fairchild Semiconductor, FAN4860 Datasheet - Page 13

• Manufacturer Part Number: FAN4860
• Description: The FAN4860 is a low-power boost regulator designed to provide a regulated 5V output from a single cell Li-Ion battery
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FAN4860 • Rev. 1.1.0
Application Information
External Component Selection
Table 2 shows the recommended external components for
the FAN4860:
Table 2.
Note:
4.
Output Capacitance (C
Stability
The effective capacitance (C
ceramic capacitors decrease as their bias voltage increases,
as shown in Figure 40.
FAN4860 is guaranteed for stable operation with the
minimum value of C
REF
C
C
L1
OUT
IN
A 6.3V-rated 0603 capacitor may be used for C
such as Murata GRM188R60J225M. All datasheet
parameters are valid with the 6.3V-rated capacitor.
Due to DC bias effects, the 10V capacitor offers a
performance enhancement; particularly output ripple
and transient response, without any size increase.
Figure 40.
1.0µH, 0.8A, 190mΩ,
0805
2.2µF, 6.3V, X5R,
0402
4.7µF, 10V, X5R,
0603
External Components
Description
(4)
C
EFF
EFF
(C
for 4.7μF, 0603, X5R, 6.3V (Murata
GRM188R60J475K)
EFF(MIN)
OUT
Murata LQM21PN1R0MC0,
or equivalent
Murata GRM155R60J225M
TDK C1005X5R0J225M
Kemet C0603C475K8PAC
TDK C1608X5R1A475K
) outlined in Table 3.
EFF
)
) of small, high-value,
Manufacturer
OUT
,
13
Table 3.
C
and temperature. Some manufacturers may be able to
provide an X5R capacitor in 0402 case size that retains C
>1.5μF with 5V bias; others may not. If this C
economically obtained and 0402 case size is required, the IC
can work with the 0402 capacitor as long as the minimum V
is restricted to >2.7V.
For best performance, a 10V-rated 0603 output capacitor is
recommended (Kemet C0603C475K8PAC, or equivalent).
Since it retains greater C
temperature, ouptut ripple can is reduced and transient
capability enhanced.
Output Voltage Ripple
Output voltage ripple is inversely proportional to C
During t
supplied by C
and
Therefore:
where:
As can be seen from Equation 4, the maximum V
occurs when V
Startup
Input current limiting is in effect during soft-start, which limits
the current available to charge C
achieve regulation within the time period described in the
soft-start section above; a FAULT occurs, causing the circuit
to shut down, then restart after a significant time period. If
C
attempt, but eventually achieves regulation if no load is
present. If a high-current load and high capacitance are both
present during soft-start, the circuit may fail to achieve
V
t
V
t
ON
SW
EFF
OUT
RIPPLE
RIPPLE
=
2.3 to 4.5
2.7 to 4.5
2.3 to 4.5
varies with manufacturer, dielectric material, case size,
=
is a very high value, the circuit may not start on the first
V
t
SW
1
IN
P (
P (
ON
Operating Conditions
f
SW
−
(V)
−
, when the boost switch is on, all load current is
) P
•
P
Minimum C
D
)
OUT
=
=
=
IN
t
t
t
ON
SW
.
is minimum and I
SW
•
•
•
I
C
⎛
⎜
⎜
⎝
LOAD
⎛
⎜
⎜
⎝
1
1
OUT
−
−
EFF
V
I
V
V
LOAD
OUT
V
OUT
0 to 200
0 to 200
0 to 150
IN
IN
Required for Stability
EFF
⎞
• ⎟ ⎟
⎠
(mA)
⎞
⎟
⎟
⎠
LOAD
I
C
OUT
LOAD
under bias and over
OUT
. If the output fails to
is maximum.
www.fairchildsemi.com
C
EFF
EFF(MIN)
cannot be
1.5
1.0
1.0
(μF)
RIPPLE
OUT
EFF
(2)
(3)
(4)
(5)
IN
.