Datasheet

LT1308A/LT1308B
15
1308abfb
APPLICATIONS INFORMATION
GSM AND CDMA PHONES
The LT1308A/LT1308B are suitable for converting a single
Li-Ion cell to 5V for powering RF power stages in GSM or
CDMA phones. Improvements in the LT1308A/LT1308B
error amplifi ers allow external compensation values to be
reduced, resulting in faster transient response compared
to the LT1308. The circuit of Figure 24 (same as Figure 1,
printed again for convenience) provides a 5V, 1A output
from a Li-Ion cell. Figure 25 details transient response at
the LT1308A operating at a V
IN
of 4.2V, 3.6V and 3V. Ripple
voltage in Burst Mode operation can be seen at 10mA
load. Figure 26 shows transient response of the LT1308B
under the same conditions. Note the lack of Burst Mode
ripple at 10mA load.
Figure 23. Load Step Response with 10μF X5R
Ceramic Output Capacitor and C
PL
Figure 25. LT1308A Li-Ion to 5V Boost Converter
Transient Response to 1A Load Step
Figure 26. LT1308B Li-Ion to 5V Boost
Converter Transient Response to 1A Load Step
1308 F23
LOAD
CURRENT
I
L1
1A/DIV
500mA
50mA
V
OUT
500mV/DIV
200µs/DIV
1308 F25
I
LOAD
1A
1mA
V
OUT
V
IN
= 4.2V
V
OUT
V
IN
= 3.6V
V
OUT
V
IN
= 3V
200µs/DIV
V
OUT
TRACES =
200mV/DIV
1308 F26
I
LOAD
1A
10mA
V
OUT
V
IN
= 4.2V
V
OUT
V
IN
= 3.6V
V
OUT
V
IN
= 3V
100µs/DIV
V
OUT
TRACES =
200mV/DIV
Figure 24. Li-Ion to 5V Boost Converter Delivers 1A
V
IN
SW
FB
LT1308B
L1
4.7µH
D1
47k
R2
100k
R1
309k
5V
1A
100pF
1308A/B F24
C1
47µF
C2
220µF
Li-Ion
CELL
V
C
GND
SHDNSHUTDOWN
C1: AVX TAJC476M010
C2: AVX TPSD227M006
+
+
D1: IR 10BQ015
L1: MURATA LQH6N4R7