LTC1874 Linear Technology, LTC1874 Datasheet - Page 11

• Manufacturer Part Number: LTC1874
• Description: Dual Constant Frequency Current Mode Step-Down DC/DC Controller
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC1874. These items are illustrated graphically for a
single controller in the layout diagram in Figure 6. Check
the following in your layout:
1. Is the Schottky diode closely connected between power
2. Does the (+) plate of C
3. Is the input decoupling capacitor (0.1 F) connected
4. Connect the end of R
ground (PGND) and the drain of the external MOSFET?
as closely as possible? This capacitor provides AC
current to the MOSFET.
closely between V
The V
IN
pin is the SENSE
U
IN
and signal ground (GND)?
SENSE
U
IN
V
connect to the sense resistor
OUT
+
V
Figure 6. LTC1874 Layout Diagram (See PC Board Layout Checklist)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
IN
as close to V
of the current comparator.
BOLD LINES INDICATE HIGH CURRENT PATHS
R2
R1
W
+
C
OUT
L1
IN
SW
as possible.
C
U
IN
D1
+
M1
0.1 F
R
SENSE
5. Is the trace from SENSE
6. Keep the switching node PGATE away from sensitive
7. Does the V
8. PV
short? Does the trace connect close to R
small signal nodes.
resistors? The resistive divider R1 and R2 must be
connected between the (+) plate of C
ground.
GND. Isolate high current power paths from signal
power and signal ground where possible in the layout.
An unbroken ground plane is recommended.
IN
1
2
3
4
V
SENSE
GND
V
must connect to V
IN
FB
1/2 LTC1874
–
I
TH
PGATE
FB
PGND
/RUN
PV
IN
pin connect directly to the feedback
16
15
14
13
R
ITH
C
1874 F06
ITH
IN
–
and PGND must connect to
to the SENSE resistor kept
LTC1874
OUT
SENSE
and signal
11
?