MAX893 Maxim, MAX893 Datasheet - Page 7

• Manufacturer Part Number: MAX893
• Description: 1.2A / Current-Limited / High-Side P-Channel Switch with Thermal Shutdown
• Manufacturer: Maxim

Figure 2. Setting the Current Limit
The MAX893L features thermal shutdown. The switch
turns off when the junction temperature exceeds
+165°C. Once the device cools by 10°C, the switch
turns back on. If the fault condition is not removed, the
switch will cycle on and off, resulting in a pulsed out-
put.
The MAX893L provides a fault output (FAULT). This
open-drain output goes low when in current limit or
when the die temperature exceeds +165°C. A 100kΩ
pull-up resistor from FAULT to IN provides a logic-
control signal.
During start-up in USB applications, the MAX893L
charges the relatively large USB capacitance. This may
activate an unwanted fault signal if the charging current
exceeds the programmed current limit. To “blank out”
this start-up fault signal, add a simple lowpass RC
delay circuit as shown in Figure 3. This circuit provides
a 10ms delay.
To limit the input voltage drop during momentary output
short-circuit conditions, connect a capacitor no more
than 5mm from IN to GND. A 1µF ceramic capacitor will
be adequate for most applications; however, higher
capacitor values will further reduce the voltage drop at
the input.
P-Channel Switch with Thermal Shutdown
Applications Information
_______________________________________________________________________________________
MAX893L
GND
SET
Thermal Shutdown
Input Capacitor
Fault Indicator
Fault Blanking
1.2A, Current-Limited, High-Side
R
SET
Connect a 0.1µF capacitor from OUT to GND to prevent
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 to reduce the effect
of undesirable parasitic inductance. Place input and
output capacitors as close to the device as possible
(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
When the output is short circuited, the voltage drop
across the switch equals the input supply. Hence, the
power dissipated across the switch increases, as does
the die temperature. If the fault condition is not
removed, the thermal-shutdown protection circuitry
turns the switch off until the die temperature falls by
10°C. A ground plane in contact with the device will
help dissipate additional heat.
TRANSISTOR COUNT: 340
Figure 3. Fault-Blanking Circuit
BLANKED
SIGNAL
TO µP
INPUT VOLTAGE
ON
is the on-resistance of the switch.
0.1 F
+5V
Layout and Thermal-Dissipation
C
100k
R
100k
P = (I
LIMIT)
Chip Information
IN
ON/OFF
FAULT
2
· R
MAX893L
Output Capacitor
ON
Considerations
GND
OUT
SET
V
R
OUT
SET
7