LTC3631IMS8E#TRPBF Linear Technology, LTC3631IMS8E#TRPBF Datasheet - Page 16

• 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
LTC3631
The undervoltage lockout requirement on V
satisfied with a resistive divider from V
HYST pins. Choose R1 = 2M and calculate R2 and R3 as
follows:
Choose standard values for R2 = 226k and R3 = 91k. The
I
mum peak current (225mA). Figure 9 shows a complete
schematic for this design example.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3631. Check the following in your layout:
1. Large switched currents flow in the power switches
16
SET
and input capacitor. The loop formed by these compo-
nents should be as small as possible. A ground plane
is recommended to minimize ground impedance.
R2 =
R3 =
pin should be left open in this example to select maxi-
24V
V
IN
Figure 9. 24V to 3.3V, 100mA Regulator at 250kHz








V
V
IN(RISING)
IN(FALLING)
1µF
1.21V
1.1V
2M
226k
91k
– 1.21V
V
RUN
HYST
– 1.1V
IN
LTC3631
GND

 • R1– R2 = 90.8k



 • R1= 224k


I
SW
V
SET
SS
FB
47µH
IN
750k
240k
to the RUN and
3631 F09
10µF
IN
V
3.3V
100mA
OUT
can be
2. Connect the (+) terminal of the input capacitor, C
3. Keep the switching node, SW, away from all sensitive
4. Flood all unused area on all layers with copper. Flooding
V
IN
close as possible to the V
the AC current into the internal power MOSFETs.
small signal nodes. The rapid transitions on the switching
node can couple to high impedance nodes, in particular
V
with copper will reduce the temperature rise of power
components. You can connect the copper areas to any
DC net (V
system).
FB
, and create increased output ripple.
V
IN
R
SET
VIAS TO GROUND PLANE
VIAS TO INPUT SUPPLY (V
OUTLINE OF LOCAL GROUND PLANE
IN
C
IN
, V
C
SS
C
OUT
SS
V
RUN
HYST
SS
, GND or any other DC rail in your
Example Layout
IN
LTC3631
C
GND
IN
GND
IN
I
SW
V
SET
IN
L1
FB
pin. This capacitor provides
)
C
OUT
L1
R
SET
R1
R2
R1
3631 F09a
V
C
R2
OUT
OUT
IN
V
3631fc
, as
OUT