LTC3631IMS8E#TRPBF Linear Technology, LTC3631IMS8E#TRPBF Datasheet - Page 13

• Manufacturer Part Number: LTC3631IMS8E#TRPBF
• Description: IC CONV STP-DWN SYNC ADJ 8-MSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3631IMS8E#TRPBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 45 V
• Current - Output: 100mA
• Voltage - Input: 4.5 ~ 45 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP Exposed Pad, 8-HMSOP, 8-eMSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Frequency - Switching: -

applicaTions inForMaTion
Output Voltage Programming
For the adjustable version, the output voltage is set by
an external resistive divider according to the following
equation:
The resistive divider allows the V
of the output voltage as shown in Figure 6. Output voltage
can range from 0.8V to V
To minimize the no-load supply current, resistor values in
the megohm range should be used; however, large resistor
values should be used with caution. The feedback divider
is the only load current when in shutdown. If PCB leak-
age current to the output node or switch node exceeds
the load current, the output voltage will be pulled up. In
normal operation, this is generally a minor concern since
the load current is much greater than the leakage. The
increase in supply current due to the feedback resistors
can be calculated from:
Run Pin with Programmable Hysteresis
The LTC3631 has a low power shutdown mode controlled
by the RUN pin. Pulling the RUN pin below 0.7V puts the
LTC3631 into a low quiescent current shutdown mode
(I
Q
V
ΔI
~ 3µA). When the RUN pin is greater than 1.2V, the
OUT
VIN
= 0.8V • 1+
=



R1+ R2
Figure 6. Setting the Output Voltage
V
OUT



LTC3631

 •

R2
R1



GND
V
V
FB
IN



V
OUT
.
IN



V
OUT
FB
R1
R2
3631 F06
pin to sense a fraction
The RUN pin can alternatively be configured as a precise
undervoltage lockout (UVLO) on the V
resistive divider from V
parator nominally provides 10% hysteresis when used in
this method; however, additional hysteresis may be added
with the use of the HYST pin. The HYST pin is an open-
drain output that is pulled to ground whenever the RUN
comparator is not tripped. A simple resistive divider can
be used as shown in Figure 8 to meet specific V
requirements.
Specific values for these UVLO thresholds can be computed
from the following equations:
controller is enabled. Figure 7 shows examples of con-
figurations for driving the RUN pin from logic.
Rising V
Falling V
V
SUPPLY
IN
IN
Figure 8. Adjustable Undervoltage Lockout
UVLO Threshold = 1.21V • 1+
UVLO Threshold = 1.10V • 1+
Figure 7. RUN Pin Interface to Logic
RUN
LTC3631
V
IN
R1
R2
R3
IN
to ground. The RUN pin com-
RUN
HYST
LTC3631
3631 F08
V
IN
4.7M
LTC3631
IN






RUN
supply with a
LTC3631
R2
R1
R2 + R3
3631 F07
IN



R1
13
voltage
3631fc


