LTC4440
10
4440fb
For more information www.linear.com/LTC4440
APPLICATIONS INFORMATION
Undervoltage Lockout (UVLO)
The LTC4440 contains both low side and high side un-
dervoltage lockout
detectors that monitor V
CC
and the
bootstrapped supply V
BOOST–TS
. When V
CC
falls below
6.2V, the internal buffer is disabled and the output pin
OUT is pulled down to TS. When V
BOOST – TS
falls below
6.9V, OUT is pulled down to TS. When both supplies are
undervoltage, OUT is pulled low to TS and the chip enters
a low current mode, drawing approximately 25µA from
V
CC
and 86µA from BOOST.
Bypassing and Grounding
The LTC4440 requires proper bypassing on the V
CC
and V
BOOST–TS
supplies due to its high speed switching
(nanoseconds) and large AC currents (Amperes). Careless
component placement and PCB trace routing may cause
excessive ringing and under/overshoot.
To obtain the optimum performance from the LTC4440:
A. Mount the bypass capacitors as close as possible
between the V
CC
and GND pins and the BOOST and
TS pins. The leads should be shortened as much as
possible to reduce lead inductance.
B. Use a low inductance, low impedance ground plane
to reduce any ground drop and stray capacitance. Re
-
member that
the LTC4440 switches >2A peak currents
and
any significant ground drop will degrade signal
integrity.
C. Plan the power/ground routing carefully. Know where
the large load switching current is coming from and
going to. Maintain separate ground return paths for
the input pin and the output power stage.
D. Keep the copper trace between the driver output pin
and the load short and wide.
E. When using the MS8E package, be sure to solder the
exposed pad on the back side of the LTC4440 package
to the board. Correctly soldered to a 2500mm
2
double-
sided 1oz copper board, the LTC4440 has a thermal
resistance of approximately 40°C/W. Failure to make
good thermal contact between the exposed back side
and the copper board will result in thermal resistances
far greater than 40°C/W.
