LTC6991 datasheet(18/24 Pages) LINER

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LTC6991

6991f

1. Connect the bypass capacitor, C1, directly to the V+ and

GND pins using a low inductance path. The connection

from C1 to the V+ pin is easily done directly on the top

layer. For the DFN package, C1’s connection to GND is

also simply done on the top layer. For the TSOT-23, OUT

can be routed through the C1 pads to allow a good C1

GND connection. If the PCB design rules do not allow

that,C1’sGNDconnectioncanbeaccomplishedthrough

multiple vias to the ground plane. Multiple vias for both

the GND pin connection to the ground plane and the

C1 connection to the ground plane are recommended

to minimize the inductance. Capacitor C1 should be a

0.1µF ceramic capacitor.

2. Place all passive components on the top side of the

board. This minimizes trace inductance.

3. Place RSET as close as possible to the SET pin and

make a direct, short connection. The SET pin is a

current summing node and currents injected into this

pin directly modulate the operating frequency. Having

a short connection minimizes the exposure to signal

pickup.

4. Connect RSET directly to the GND pin. Using a long path

or vias to the ground plane will not have a significant

affect on accuracy, but a direct, short connection is

recommended and easy to apply.

5. Use a ground trace to shield the SET pin. This provides

another layer of protection from radiated signals.

6. Place R1 and R2 close to the DIV pin. A direct, short

connection to the DIV pin minimizes the external signal

coupling.

6991 F18

LTC6991

RST

GND

SET

OUT

V+

DIV

0.1µF

RSET

V+

DIV

SET

OUT

GND

RST

V+

RSET

DFN PACKAGE

RST

GND

SET

OUT

V+

DIV

V+

RSET

TSOT-23 PACKAGE

Figure 18. Supply Bypassing and PCB Layout

applicaTions inForMaTion

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