LT1301I LINER [Linear Technology], LT1301I Datasheet - Page 6

• Manufacturer Part Number: LT1301I
• Description: Micropower High Efficiency 5V/12V Step-Up DC/DC Converter for Flash Memory
• Manufacturer: LINER [Linear Technology]

APPLICATIONS
LT1301
6
Output Voltage Selection
The LT1301 can be selected to 5V or 12V under logic
control or fixed at either by tying Select to ground or V
respectively. It is permissible to tie Select to a voltage
higher than V
Efficiency in 5V mode will be slightly less that in 12V mode
due to the fact that the diode drop is a greater percentage
of 5V than 12V. Since the bipolar switch in the LT1301 gets
its base drive from V
occurs when in 5V mode. When V
grammed output voltage the output will follow the input.
This is characteristic of the simple step-up or “boost”
converter topology. A circuit example that provides a
regulated output with an input voltage above or below the
output (known as a buck-boost or SEPIC) is shown in the
Typical Applications section.
Shutdown
The converter can be turned off by pulling SHDN (pin 3)
high. Quiescent current drops to 10 A in this condition.
Bias current of 8 A to 10 A flows into the pin (at 5V input).
It is recommended that SHDN not be left floating. Tie the
pin to ground if the feature is not used. SHDN can be driven
high even if V
I
The LT1301’s current limit (I
start. Upon start-up, the LT1301 will draw maximum
current from the supply (about 1A) from the supply to
charge the output capacitor. Figure 5 shows V
waveforms as the 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
LIM
AC COUPLED
100mV/DIV
500mA/DIV
Function
10V/DIV
V
V
OUT
SW
I
L
Figure 4. Burst Mode Operation in Action
V
C
IN
OUT
= 5V, V
IN
= 33 F, I
IN
is floating.
OUT
as long as it does not exceed 10V.
U
LOAD
= 12V, L = 33 H
IN
, no reduction in switch efficiency
= 90mA
INFORMATION
U
20 s/DIV
LIM
) pin can be used for soft
W
IN
exceeds the pro-
LT1300 F4
OUT
U
and I
IN
IN
adding R1 and C3 as shown in Figure 6, the switch
current in the LT1301 is initially limited to 400mA until
the 15 A flowing out of the I
current is held to under 500mA while the output voltage
ramps up to 12V as shown in Figure 7. R1 provides a
discharge path for the capacitor without appreciably de-
creasing peak switch current. When using the I
start mode a minimum load of a few hundred microam-
peres is recommended to prevent C3 from discharging, as
no current flows out of I
3.3V OR 5V
500mA/DIV
500mA/DIV
Figure 7. Startup Response Soft-Start Circuitry Added
V
IN
10V/DIV
10V/DIV
5V/DIV
V
5VDIV
V
V
SHDN
V
SHDN
OUT
OUT
I
+
I
IN
IN
SHUTDOWN
V
47µF
IN
V
IN
= 5V, V
= 5V, V
Figure 5. Start-Up Response
OUT
OUT
= 12V
SHDN
= 12V
SELECT
GND
V
IN
Figure 6.
200 s/DIV
LT1301
200 s/DIV
33µH
LIM
L1
LIM
when the LT1301 is not
SENSE
PGND
pin charges up C3. Input
SW
I
LIM
1N5817
R1
1M
D1
LT1300 F5
LT1300 F5
LIM
C3
0.1µF
pin soft-
+
LT1301 F6
C2
33µF
12V