ml4875 ETC-unknow, ml4875 Datasheet - Page 8

• Manufacturer Part Number: ml4875
• Description: Voltage Boost Regulator With Shutdown
• Manufacturer: ETC-unknow

ML4875
INPUT CAPACITOR
Unless the input source is a very low impedance battery,
it will be necessary to decouple the input with a capacitor
with a value of between 47µF and 100µF. This provides
the benefits of preventing input ripple from affecting the
ML4875 control circuitry, and it also improves efficiency
by reducing I-squared R losses during the charge and
discharge cycles of the inductor. Again, a low ESR
capacitor (such as tantalum) is recommended.
DRIVING THE SHDN INPUT
Unlike other boost regulators which use external Schottky
diodes, the ML4875 has the ability to isolate the load from
the battery input when the SHDN pin is high. Since there
may be no other voltage available when the regulator is in
shutdown, the SHDN input threshold is set well below the
minimum V
an open collector device with a high value pull-up resistor
to V
device, a resistor divider should be used to prevent the
SHDN input high level from exceeding V
the SHDN input low level is below the 200mV threshold.
SETTING THE RESET THRESHOLD
To use the RESET comparator as an input voltage monitor,
it is necessary to use an external resistor divider tied to the
DETECT pin as shown in the block diagram. The resistor
values R
equation:
The value of R
current errors. R
equation:
8
IN
. If SHDN is driven from a TTL or CMOS output
A
and R
IN
voltage. SHDN can be driven directly from
B
B
A
should be 100ký or less to minimize bias
V
R
can be calculated using the following
is then found by rearranging the
IN MIN
A
(
R
)
B
0 2
.
V
IN MIN
. 0 2
(
(
R
A
R
)
B
R
1
B
)
IN
, and to ensure
(5)
(6)
LAYOUT
Good PC board layout practices will ensure the proper
operation of the ML4875. Important layout considerations
include:
• Use adequate ground and power traces or planes
• Keep components as close as possible to the ML4875
• Use short trace lengths from the inductor to the V
• Use a single point ground for the ML4875 ground pins,
and from the output capacitor to the V
and the input and output capacitors
OUT
pin
L
pin