DRV102F datasheet(9/23 Pages) TI

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DRV102

SBVS009A

www.ti.com

CONSTANT OUTPUT DURATION

(Delay Time to PWM Mode)

µs

Pin Connected to 5V

µs

Pin Open

µs

100pF

0.97ms

1nF

97ms

0.1

µF

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-

TABLE I. Delay Adjust Pin Connections.

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 • 10

(time in seconds, CD in Farads)

Leaving the Delay Adjust pin open results in a constant

output time of approximately 15

µs. The duration of this

initial output can be reduced to less than 3

µs 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.

FIGURE 2. Location of External Flyback Diode.

The internal Delay Adjust circuitry is composed of a 3

µA

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).

FIGURE 3. Simplified Circuit Model of the Delay Adjust Pin.

DRV102

Load

Out

2a) Flyback Diode Near DRV102

DRV102

Load

Out

2b) Flyback Diode Near Load

µA

3V Reference

Comparator

Delay Adjust

DRV102

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