LTC3809EMSE-1 Linear Technology, LTC3809EMSE-1 Datasheet - Page 16

• Manufacturer Part Number: LTC3809EMSE-1
• Description: IC CTRLR DC/DC SYNC 10-MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3809EMSE-1

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 9.8 V
• Current - Output: 1A
• Frequency - Switching: 550kHz
• Voltage - Input: 2.75 ~ 9.8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP Exposed Pad, 10-HMSOP, 10-eMSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC3809-1
For most applications, a 59k resistor is suggested for R
In applications where minimizing the quiescent current is
critical, R
divider current. If R
it may be benefi cial to bypass R
capacitor C
Run and Soft-Start/Tracking Functions
The LTC3809-1 has a low power shutdown mode which is
controlled by the RUN pin. Pulling the RUN pin below 1.1V
puts the LTC3809-1 into a low quiescent current shutdown
mode (I
(at V
to V
driven directly from logic as showed in Figure 4.
16
IN
IN
3.3V OR 5V
, which enables the controller. The RUN pin can be
Q
= 4.2V) current source will pull the RUN pin up
= 9μA). Releasing the RUN pin, an internal 0.7μA
A
FF
should be made bigger to limit the feedback
.
Figure 3. Setting Output Voltage
Figure 4. RUN Pin Interfacing
LTC3809-1
LTC3809-1
RUN
B
then results in very high impedance,
V
FB
V
OUT
R
R
38091 F03
B
B
A
with a 50pF to 100pF
C
FF
LTC3809-1
RUN
38091 F04
A
.
Once the controller is enabled, the start-up of V
trolled by the state of the TRACK/SS pin. If the TRACK/SS
pin is connected to V
by internal soft-start, which slowly ramps the positive
reference to the error amplifi er from 0V to 0.6V, allowing
V
internal soft-start time is around 0.74ms. The soft-start
time can be changed by placing a capacitor between the
TRACK/SS pin and GND. In this case, the soft-start time
will be approximately:
where 1μA is an internal current source which is always on.
When the voltage on the TRACK/SS pin is less than the
internal 0.6V reference, the LTC3809-1 regulates the V
voltage to the TRACK/SS pin voltage instead of 0.6V.
Therefore the start-up of V
an external voltage V
tor divider at TRACK/SS pin (Figure 5a). The ratiometric
relation between V
OUT
t
V
SS
V
OUT
to rise smoothly from 0V to its fi nal value. The default
X
=
Figure 5a. Using the TRACK/SS Pin to Track V
=
C
SS
R
R
TA
A
•
600
•
V
1
R
X
OUT
R
μ
TA
R
R
mV
TB
TA
A
A
X
IN
, according to a ratio set by a resis-
+
+
, the start-up of V
and V
TRACK/SS
R
R
LTC3809-1
B
TB
OUT
X
38091 F5a
V
is (Figure 5c):
FB
can ratiometrically track
V
OUT
R
R
B
A
OUT
is controlled
OUT
X
is con-
38091fc
FB