LT3505EMS8E#PBF Linear Technology, LT3505EMS8E#PBF Datasheet - Page 17

• Manufacturer Part Number: LT3505EMS8E#PBF
• Description: IC REG SW STP DWN 1.2A 8-MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LT3505EMS8E#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.78 ~ 33.8 V
• Current - Output: 1.2A
• Frequency - Switching: 200kHz ~ 3MHz
• Voltage - Input: 3.6 ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP Exposed Pad, 8-HMSOP, 8-eMSOP
• Dc To Dc Converter Type: Step Down
• Pin Count: 8
• Input Voltage: 36V
• Output Voltage: 0.78 to 33.84V
• Switching Freq: 200 TO 3000KHz
• Output Current: 1.2A
• Package Type: MSOP EP
• Output Type: Adjustable
• Switching Regulator: Yes
• Line Regulation: 0.007%/V(Typ)
• Mounting: Surface Mount
• Input Voltage (min): 3.6V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Compliant

APPLICATIONS INFORMATION
Figure 8. To Soft-Start the LT3505, Add a Resistor and Capacitor
to the SHDN pin. V
5Ω, R
0.068 F
RUN
T
15k
= 20.0k, L = 2.5µH
RUN
5V/DIV
1A/DIV
2V/DIV
5V/DIV
1A/DIV
2V/DIV
V
V
V
V
OUT
OUT
SW
SW
I
I
L
L
V
V
L = 2.5 H
C
R
V
V
L = 2.5 H
C
R
SHDN
SHDN
IN
OUT
OUT
T
IN
OUT
OUT
T
= 20.0k
= 20.0k
= 12V
= 12V
IN
GND
= 3.3V
= 10 F
GND
= 3.3V
= 10 F
= 12V, V
OUT
10 s/DIV
10 s/DIV
= 3.3V, C
OUT
= 10µF, R
3505 F08b
3505 F08a
LOAD
=
plications or in battery backup systems where a battery
or some other supply is diode OR-ed with the LT3505’s
output. If the V
is held high (either by a logic signal or because it is tied
to V
quiescent current through its SW pin. This is fi ne if your
system can tolerate a few mA in this state. If you ground
the SHDN pin, the SW pin current will drop to essentially
zero. However, if the V
is held high, then parasitic diodes inside the LT3505 can
pull large currents from the output through the SW pin
and the V
when the input voltage is present and that protects against
a shorted or reversed input.
Figure 9. Diode D4 Prevents a Shorted Input from Discharging
a Backup Battery Tied to the Output; It Also Protects the Circuit
from a Reversed Input. The LT3505 Runs Only When the Input
is Present
Hot Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT3505 circuits. However, these ca-
pacitors can cause problems if the LT3505 is plugged into
a live supply (see Linear Technology Application Note 88
for a complete discussion). The low loss ceramic capacitor
combined with stray inductance in series with the power
source forms an underdamped tank circuit and the voltage
at the V
input voltage, possibly exceeding the LT3505’s rating and
V
IN
IN
), then the LT3505’s internal circuitry will pull its
D4
IN
IN
pin of the LT3505 can ring to twice the nominal
pin. Figure 9 shows a circuit that will run only
V
SHDN
R
IN
IN
T
BOOST
LT3505
pin is allowed to fl oat and the SHDN pin
GND
IN
SW
V
FB
C
pin is grounded while the output
LT3505
3505 F09
17
V
BACKUP
OUT
3505fc