lt3689-5 Linear Technology Corporation, lt3689-5 Datasheet - Page 26

• Manufacturer Part Number: lt3689-5
• Description: 700ma Step-down Regulator With Power-on Reset And Watchdog Timer
• Manufacturer: Linear Technology Corporation

LT3689/LT3689-5
the LT3689’s output. If the V
the EN/UVLO pin is held high (either by a logic signal or
because it is tied to V
will pull its quiescent current through its SW pin. This is
fi ne if the system can tolerate a few mA in this state. If the
EN/UVLO pin is grounded, the SW pin current will drop to
essentially zero. However, if the V
the output is held high, then parasitic diodes inside the
LT3689 can pull large currents from the output through
the SW pin and the V
will run only when the input voltage is present and that
protects against a shorted or reversed input.
APPLICATIONS INFORMATION
26
IN
IN
), then the LT3689’s internal circuitry
pin. Figure 14 shows a circuit that
IN
pin is allowed to fl oat and
IN
Figure 15. Example Layout for QFN Package.
A Good PCB Layout Ensures Proper Low EMI Operation
pin is grounded while
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 15 shows
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
currents fl ow in the LT3689’s V
diode (D1) and the input capacitor (C1). The loop formed
by these components should be as small as possible.
These components, along with the inductor and output
capacitor, should be placed on the same side of the circuit
board. Place a local, unbroken ground plane below these
components. The SW and BST nodes should be as small
IN
and SW pins, the catch
3689fa