Datasheet
LTC1700
14
1700fa
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC1700. These items are illustrated graphically in the
layout diagram in Figure 8. Check the following in your
layout:
1. Are all the components connected close to the SW node
(Pin 10)? The SW pin is the input to the V
DS
sense
amplifier and the current reverse comparator.
2. Connect the V
OUT
lead directly to the source of the
P-channel MOSFET. Besides supplying current to the
LTC1700, it also serves as the other input to the current
reverse comparator.
Figure 8. LTC1700 Layout Diagram (See PC Board Layout Checklist)
3. Connect the (+) plate of C2 to the source of the P-channel
MOSFET. This capacitor supports the load current when
the inductor is being “recharged”.
4. Connect the (–) plate of C2 to the source of the N-channel
MOSFET. Connect the power and signal ground to this
node.
5. Does the V
FB
pin connect directly to the feedback
resistors? The resistive divider R1 and R2 must be con-
nected between the (+) plate of C2 and signal ground.
6. Keep the switching node SW away from sensitive small
signal nodes.
7. Switched currents flow in M1, M2 and C2, keep the loop
formed by these components as small as possible.
APPLICATIONS INFORMATION
WUU
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Figure 7. Design Example Schematic
SGND
I
TH
V
FB
RUN/SS
SYNC/MODE
SW
PGND
BG
V
OUT
TG
LTC1700
1
2
3
4
5
10
9
8
7
6
+
L1
C1
C2
C4
C3
R3
M2
M1
V
IN
V
OUT
1700 • F08
R1
R2
SGND
I
TH
RUN/SS
V
FB
SYNC/MODE
SW
BG
PGND
TG
V
OUT
LTC1700
1
2
4
3
5
10
8
9
6
7
+
L1
3.2µH
C3
22µF
C1
22µF
C4
470µF
6.3V
×2
270pF
470pF
3.9nF
5k
316k
100k
M2
Si9803
M1
IR7811W
V
IN
3.3V
V
OUT
5V/3A
1700 • F07
+
C2
68µF
6.3V
C1, C3: TAIYO YUDEN CERAMIC JMK316BJ106ML
C2: AVX TAJB68K006R
C4: SANYO POSCAP 6TPB470M
L1: SUMIDA CEP1233R2
M1: INTERNATIONAL RECTIFIER IR7811W
M2: SILICONIZ Si9803