LT1304-5 LINER [Linear Technology], LT1304-5 Datasheet - Page 7

• Manufacturer Part Number: LT1304-5
• Description: Micropower DC/DC Converters with Low-Battery Detector Active in Shutdown
• Manufacturer: LINER [Linear Technology]

OPERATIO
Table 1 lists inductor suppliers along with appropriate part
numbers.
Table 1. Recommended Inductors
VENDOR
Sumida
Coiltronics
Dale
Coilcraft
Capacitor Selection
Low ESR (Equivalent Series Resistance) capacitors should
be used at the output of the LT1304 to minimize output
ripple voltage. High quality input bypassing is also re-
quired. For surface mount applications AVX TPS series
tantalum capacitors are recommended. These have been
specifically designed for switch mode power supplies and
have low ESR along with high surge current ratings. A
100 F, 10V AVX TPS surface mount capacitor typically
limits output ripple voltage to 70mV when stepping up
from 2V to 5V at a 200mA load. For through hole applica-
tions Sanyo OS-CON capacitors offer extremely low ESR
in a small package size. Again, if peak switch current is
reduced using the I
eased and smaller, higher ESR units can be used. Sug-
gested capacitor sources are listed in Table 2.
Table 2. Recommended Capacitors
VENDOR
AVX
Sanyo
Sprague
Diode Selection
Best performance is obtained with a Schottky rectifier
such as the 1N5818. Motorola makes the MBRS130L
Schottky which is slightly better than the 1N5818 and
comes in a surface mount package. For lower switch
currents, the MBR0530 is recommended. It comes in a
very small SOD-123 package. Multiple 1N4148s in parallel
can be used in a pinch, although efficiency will suffer.
SERIES
TPS
OS-CON
595D
CD54, CD43
CTX20-1
LPT4545
DO3316, DO1608, DO3308
SERIES
U
LIM
pin, capacitor requirements can be
TYPE
Surface Mount
Through Hole
Surface Mount
PHONE NUMBER
[phone]
[phone]
[phone]
[phone]
PHONE NUMBER
[phone]
[phone]
[phone]
I
The LT1304’s current limit (I
start. Upon start-up, the LT1304 will draw maximum
current (about 1A) from the supply to charge the output
capacitor. Figure 3 shows V
device is turned on. The high current flow can create IR
drops along supply and ground lines or cause the input
supply to drop out momentarily. By adding R1 and C1 as
shown in Figure 4, the switch current is initially limited to
well under 1A as detailed in Figure 5. Current flowing into
C1 from R1 and the I
R1 effectively takes C1 out of the circuit. R1 also provides
a discharge path for C1 when SHUTDOWN is brought low
for turn-off.
LIM
Figure 3. Start-Up Response. Input Current Rises Quickly to
1A. V
20mA Load
*SUMIDA CD54-220
Figure 4. 2-Cell to 5V/200mA Boost Converter Takes Four
External Parts. Components with Dashed Lines Are for
Soft Start (Optional)
Function
2 CELLS
LT1304/LT1304-3.3/LT1304-5
500mA/DIV
OUT
10V/DIV
2V/DIV
V
+
Reaches 5V in Approximately 1ms. Output Drives
V
SHDN
OUT
I
IN
100 F
LIM
LBI
LB0
GND
V
IN
pin will eventually charge C1 and
LT1304-5
22 H*
OUT
1ms/DIV
LIM
+
SENSE
I
SW
SHDN
LIM
and V
) pin can be used for soft
MBRS130L
C1
1 F
1M
IN
R1
SHUTDOWN
waveforms as the
1304 F03
+
5V
200mA
100 F
1304 F04
7