MAX895LC/D Maxim Integrated, MAX895LC/D Datasheet - Page 7

• Manufacturer Part Number: MAX895LC/D
• Description: Power Switch ICs - Power Distribution Current-Limited High-Side P-Channel Dual Switches with Thermal Shutdown
• Manufacturer: Maxim Integrated

Specifications of MAX895LC/D

• Number Of Outputs: 2
• On Resistance (max): 500 mOhms
• On Time (max): 200 us
• Off Time (max): 20 us
• Operating Supply Voltage: 2.7 V to 5.5 V

The MAX894L/MAX895L P-channel MOSFET power
switches limit output current to a user-programmed
level. When the output current is increased beyond the
set current level, the current also increases through the
replica switch (I
(Figure 1). The current-limit error amplifier compares
the voltage across R
and regulates the current back to the lesser of the pro-
grammed current limit (I
limit (I
These switches are not bidirectional; therefore, the
input voltage must be higher than the output voltage.
The MAX894L/MAX895L feature internal current-limiting
circuitry with maximum programmable values (I
500mA, and 250mA, respectively. For best perfor-
mance, set the current limit (I
I
throughout the input supply-voltage range.
Program the current limit with a resistor (R
nected from SET_ to ground (Figure 2) as follows:
where I
and I
the MAX894L and 1050A/A for the MAX895L.
The MAX894L/MAX895L are short-circuit-protected
switches. In the event of an output short circuit or cur-
rent-overload condition, the current through either switch
is limited by the internal current-limiting error amplifier to
1.5 x I
replica error amplifier sets the current limit back to I
For a high ∆V
tion, the switch turns off and disconnects the input supply
from the output. The current-limiting amplifier then slowly
turns the switch on with the output current limited to
1.5 x I
limit is set back to I
graphs in the Typical Operating Characteristics.
The MAX894L/MAX895L feature thermal shutdown. The
switch turns off when the junction temperature exceeds
+135°C. Once the device cools by 10°C, the switch turns
back on. If the fault short-circuit condition is not
removed, the switch cycles on and off, resulting in a
pulsed output.
_______________Detailed Description
LIMIT
I
R
SET
RATIO
SET
SET
MAX
LIMIT
≤ I
LIMIT
= I
. When the fault condition is removed, the current
).
= 1.24V / I
MAX
LIMIT
is the I
. When the fault condition is removed, the
Dual, Current-Limited, High-Side P-Channel
is the desired current limit for either switch
DS
. This current limit remains in effect
OUT
/∆t during an output short-circuit condi-
/ I
OUT
_______________________________________________________________________________________
LIMIT
RATIO
/1050) (MAX895) and through R
SET
SET
to I
Setting the Current Limit
. Refer to Current-Limit Response
= (1.24V x I
LIMIT
to the internal 1.24V reference,
Short-Circuit Protection
SET
) or the maximum current
LIMIT
current ratio (1085A/A for
Thermal Shutdown
Switches with Thermal Shutdown
) between 0.2I
RATIO
) / I
SET_
LIMIT
MAX
MAX
) con-
LIMIT
SET
) of
≤
.
To limit input voltage drop during momentary output
short-circuit conditions, place a capacitor from IN to
GND. A 1µF ceramic capacitor is adequate for most
applications; however, higher capacitor values further
reduce voltage drop at the input.
Connect a 0.1µF capacitor from OUT to GND. This
capacitor prevents inductive parasitics from pulling
OUT negative during turn-off.
To take full advantage of the switch-response time to
output short-circuit conditions, it is very important to
keep all traces as short as possible, reducing the effect
of undesirable parasitic inductance. Place input and
output capacitors as close as possible to the device
(no more than 5mm).
Under normal operating conditions, the package can
dissipate and channel heat away. Calculate the maxi-
mum power as follows:
where R
switches A and B, respectively.
When one or both outputs are short circuited, the volt-
age drop across the switch equals the input supply.
Hence, the power dissipated across the switch increas-
es, as does the die temperature. If the fault condition is
not removed, the thermal-overload-protection circuitry
turns the switch off until the die temperature falls by
10°C. A ground plane in contact with the device helps
to further dissipate heat.
Figure 2. Setting the Current Limit
__________Applications Information
P = I
ONA
2 LIMITA
Layout and Thermal-Dissipation
and R
x R
MAX894L
MAX895L
ONB
ONA
are the on-resistances of
GND
SET
+ I
2 LIMITB
Output Capacitor
Input Capacitor
Consideration
R SET
x R
ONB
7