DRV102 Datasheet, PDF (9/23 Pages) Burr-Brown (TI) – PWM SOLENOID/VALVE DRIVER

APPLICATIONS INFORMATION
POWER SUPPLY
The DRV102 operates from a single +8V to +60V supply
with excellent performance. Most behavior remains un-
changed throughout the full operating voltage range. Param-
eters which vary significantly with operating voltage are
shown in the Typical Performance Curves.
CONNECTIONS TO LOAD
The PWM switching voltage and currents can cause electro-
magnetic radiation. Proper physical layout of the load cur-
rent will help minimize radiation. Load current flows from
the DRV102 output terminal to the load and returns through
the ground return path. This current path forms a loop. To
minimize radiation, make the area of the enclosed loop as
small as possible. Twisted pair leading to the load is excel-
lent. If the ground return current must flow through a chassis
ground, route the output current line directly over the chassis
surface in the most direct path to the load.
FLYBACK DIODE LOCATION
Physical location of the flyback diode may affect electro-
magnetic radiation. With most solenoid loads, inductance is
large enough that load current is virtually constant during
PWM operation. When the switching transistor is off, load
current flows though the flyback diode. If the flyback diode
is located near the DRV102 (Figure 2a), the current flowing
in long lines to the load is virtually constant. If the flyback
diode is, instead, located directly across the load (Figure 2b),
pulses of current must flow from the DRV102 to the distant
load. While theory seems to favor placing the diode at the
DRV102 output (constant current in the long lines), indi-
2a) Flyback Diode Near DRV102
DRV102
5
V_S
6
Out
4
Load
2b) Flyback Diode Near Load
DRV102
5
V_S
6
Out
4
Load
vidual situations may defy logic; if one location seems to
create noise problems, try the other.
SERIES DIODE FOR INDUCTIVE LOADS
An additional bias diode, located in series with the output, is
required when driving inductive loads. Any silicon diode,
such as the 1N4002, appropriately rated for current will
work. The diode biases the emitter of the internal power
device such that it can be fully shut off during the “off”
portion of the PWM cycle. Note that the voltage at the load
drops below ground due to the flyback diode. If it is not used,
apparent leakage current can rise to hundreds of milliamps,
resulting in unpredictable operation and thermal shutdown.
ADJUSTABLE INITIAL 100% DUTY CYCLE
A unique feature of the DRV102 is its ability to provide an
initial constant dc output (100% duty cycle) and then switch
to PWM mode to save power. This function is particularly
useful when driving solenoids which have a much higher
pull-in current requirement than hold current requirement.
The duration of this constant dc output (before PWM output
begins) can be externally and independently controlled with
a capacitor connected from Delay Adjust (pin 2) to ground
according to the following equation:
Delay Time ≈ C_D • 10⁶
(time in seconds, C_D in Farads)
Leaving the Delay Adjust pin open results in a constant
output time of approximately 15µs. The duration of this
initial output can be reduced to less than 3µs by connecting
the pin to 5V. Table I provides examples of desired “delay”
times (constant output before PWM mode) and the appropri-
ate capacitor values or pin connection.
CONSTANT OUTPUT DURATION
(Delay Time to PWM Mode)
3µs
15µs
97µs
0.97ms
97ms
C_D
Pin Connected to 5V
Pin Open
100pF
1nF
0.1µF
TABLE I. Delay Adjust Pin Connections.
The internal Delay Adjust circuitry is composed of a 3µA
current source and a 3V comparator as shown in Figure 3.
Thus, when the pin voltage is less than 3V, the output device
is 100% on (dc output mode).
DRV102
V_S
3V Reference
3µA
2
Delay Adjust
C_D
Comparator
FIGURE 2. Location of External Flyback Diode.
DRV102
SBVS009A
FIGURE 3. Simplified Circuit Model of the Delay Adjust Pin.
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