Datasheet

10
LTC1550L/LTC1551L
APPLICATIONS INFORMATION
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Figure 7. Output Ripple vs Input Bypass Capacitance
INPUT CAPACITANCE (µF)
0.1
OUTPUT RIPPLE (mV
P-P
)
8
7
6
5
4
3
2
1
0
1 10 100
1550L/51L F08
V
CC
= 5V
T
A
= 25°C
C
OUT
= 10µF
Output Ripple vs Input Bypass Capacitor
The input bypass capacitor (C
IN
) can also have a fairly
significant impact on the output ripple. C
IN
provides most
of the LTC1550L/LTC1551L’s supply current while it is
charging the flying capacitor (C1). Inadequate input
bypassing can cause the V
CC
supply to dip when the
charge pump switches, causing the output linear regulator
to momentarily stop regulating. C
IN
should be mounted as
close to the LTC1550L/LTC1551L V
CC
and GND pins as
possible and its value should be significantly larger than
C1. Surface mount tantalum or ceramic capacitors with
low ESR generally provide adequate performance. Figure␣ 7
shows the LTC1550L/LTC1551L peak-to-peak output ripple
vs C
IN
, taken using the test circuit in Figure 3 with I
LOAD
set
at 5mA. C
OUT
is a 10µF in parallel with a 0.1µF ceramic
capacitor.
A 2.2µF surface mount ceramic capacitor at V
CC
generally
provides adequate output ripple performance for most
applications.
1
2
4.5V ≤ V
CC
≤ 5.25V
8
7
REG
CP
OUT
SHDN
V
CC
C1
+
V
OUT
LTC1550L-4.1
–4.1V BIAS
GND
C1
–
C
OUT
10µF
1550L/51L TA02
C
CP
0.1µF
GaAs
TRANSMITTER
C1
0.1µF
C
IN
2.2µF
3
4
6
5
C
L
0.1µF
+
+
–4.1V Output GaAs FET Bias Generator
TYPICAL APPLICATION
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