V

O +

V

OUT)

–V

OUT– +

Av VIN)–VIN–

DRV593

DRV594

SLOS401C – OCTOBER 2002 – REVISED JULY 2010

www.ti.com

For a 100 mF electrolytic capacitor, an ESR of 0.1 Ω is common. If the 10 µH inductor is used, delivering 250 mA

of ripple current to the capacitor (as calculated above), then the ripple voltage is 25 mV. This is over ten times

that of the 10 mF ceramic capacitor, as ceramic capacitors typically have negligible ESR.

SWITCHING FREQUENCY CONFIGURATION: OSCILLATOR COMPONENTS ROSC and COSC AND

FREQ OPERATION

The onboard ramp generator requires an external resistor and capacitor to set the oscillation frequency. The

frequency may be either 500 kHz or 100 kHz by selecting the proper capacitor value and by holding the FREQ

pin either low (500 kHz) or high (100 kHz). Table 2 shows the values required and FREQ pin configuration for

each switching frequency.

Table 2. Frequency Configuration Options

SWITCHING FREQUENCY

ROSC

COSC

FREQ

500 kHz

120 k

Ω

220 pF

LOW (GND)

100 kHz

120 k

Ω

1 nF

HIGH (VDD)

For proper operation, the resistor ROSC should have 1% tolerance while capacitor COSC should be a ceramic type

with 10% tolerance. Both components should be grounded to AGND, which should be connected to PGND at a

single point, typically where power and ground are physically connected to the printed-circuit board.

EXTERNAL CLOCKING OPERATION

To synchronize the switching to an external clock signal, pull the INT/EXT terminal low, and drive the clock signal

into the COSC terminal. This clock signal must be from 10% to 90% duty cycle and meet the voltage

requirements specified in the electrical specifications table. Since the DRV593 and DRV594 include an internal

frequency doubler, the external clock signal must be approximately 250 kHz. Deviations from the 250 kHz clock

frequency are allowed and are specified in the electrical characteristic table. The resistor connected from ROSC

to ground may be omitted from the circuit in this mode of operation—the source is disconnected internally.

INPUT CONFIGURATION: DIFFERENTIAL AND SINGLE-ENDED

If a differential input is used, it should be biased around the midrail of the DRV593 or DRV594 and must not

exceed the common-mode input range of the input stage (see the operating characteristics at the beginning of

the data sheet).

The most common configuration employs a single-ended input. The unused input should be tied to VDD/2, which

may be simply accomplished with a resistive voltage divider. For the best performance, the resistor values

chosen should be at least 100 times lower than the input resistance of the DRV593 or DRV594. This prevents

the bias voltage at the unused input from shifting when the signal input is applied. A small ceramic capacitor

should also be placed from the input to ground to filter noise and keep the voltage stable. An op amp configured

as a buffer may also be used to set the voltage at the unused input.

FIXED INTERNAL GAIN

The differential output voltage may be calculated using Equation 10:

(10)

AV is the voltage gain, which is fixed internally at 2.3 V/V for DRV593 and 14.5 V/V for DRV594. The maximum

and minimum ratings are provided in the electrical specification table at the beginning of the data sheet.

POWER SUPPLY DECOUPLING

To reduce the effects of high-frequency transients or spikes, a small ceramic capacitor, typically 0.1 mF to 1 mF,

should be placed as close to each set of PVDD pins of the DRV593 and DRV594 as possible. For bulk

decoupling, a 10 mF to 100 mF tantalum or aluminum electrolytic capacitor should be placed relatively close to

the DRV593 and DRV594.

16

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