UDQ2549B Allegro MicroSystems, Inc., UDQ2549B Datasheet - Page 4

• Manufacturer Part Number: UDQ2549B
• Description: Protected Quad Power Driver
• Manufacturer: Allegro MicroSystems, Inc.

2549
PROTECTED
QUAD POWER DRIVER
0
NORMAL LAMP IN-RUSH CURRENT
T
TEMP. LIMIT
J
JUNCTION
I
= 165 C
TRIP
T < 150 C
J
OUTPUT CURRENT, I
THERMAL GRADIENT SENSING
CURRENT LIMIT
V
OUT(SAT)
TIME
GRADIENT
THERMAL
SENSING
NOT TO SCALE
OUT
NOT TO SCALE
I
Dwg. WP-008
TRIP
Dwg. GP-013
poor lamp reliability and destroy semiconductor lamp drivers. Warming
or current-limiting resistors protect both driver and lamp but use signifi-
cant power either when the lamp is OFF or when the lamp is ON,
respectively. Lamps with steady-state current ratings up to 600 mA
can be driven by these devices without the need for warming (parallel)
or current-limiting (series) resistors.
is at minimum resistance and would normally allow a 10x to 12x in-rush
current. With the these drivers, during turn-ON, the high in-rush current
is sensed by the internal low-value sense resistor. Drive current to the
output stage is then diverted by the shunting transistor, and the load
current is momentarily limited to approximately 1.0 A. During this short
transition period, the output current is reduced to a value dependent on
supply voltage and filament resistance. During lamp warmup, the
filament resistance increases to its maximum value, the output stage
goes into saturation and applies maximum rated voltage to the lamp.
directly. The internal flyback diodes prevent damage to the output
transistors by suppressing the high-voltage spikes which occur when
turning OFF an inductive load. For rapid current decay (fast turn-OFF
speeds), the use of Zener diodes will raise the flyback voltage and
improve performance. However, the peak voltage must not exceed the
specified minimum sustaining voltage (V
increase. As described above, the drive current to the affected output
stage is reduced, causing the output stage to go linear, limiting the peak
output current to approximately 1 A. As the power dissipation of that
output stage increases, a thermal gradient sensing circuit will become
operational, further decreasing the drive current to the affected output
stage and reducing the output current to a value dependent on supply
voltage and load resistance.
perature to reach approximately 165 C will result in an additional
reduction in output current to maintain a safe level.
normal saturated condition.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
High incandescent lamp turn-ON/in-rush currents can contribute to
When an incandescent lamp is initially turned ON, the cold filament
Bifilar (unipolar) stepper motors, relays, or solenoids can be driven
In the event of a shorted load, the load current will attempt to
Continuous or multiple overload conditions causing the chip tem-
If the fault condition is corrected, the output stage will return to its
SUPPLY
+ V
Z
+ V
F
V
OUT(SUS)
).