10

®

DRV102

FIGURE 6. Simplified Circuit Model of the Duty Cycle

Adjust Pin.

FIGURE 5. Using a Voltage Source to Program Duty Cycle.

DRV102

D/A

Converter

(or analog

voltage)

1k

PWM

V

PWM

3

Gnd 4

6

5

V

S

Out

NOTE: (1) Required if voltage source can go below 0.1V.

200

µA

3

V

S

Comparator

Duty Cycle

Adjust

DRV102

19k

Ω

Resistor or

NOTE: (1) Do not drive pin below 0.1V.

3.8V

0.7V

f = 24kHz

ADJUSTABLE DUTY CYCLE

The DRV102’s externally adjustable duty cycle provides an

accurate means of controlling power delivered to the load.

Duty cycle can be set from 10% to 90% with an external

resistor, analog voltage, or the output of a D/A converter.

Reduced duty cycle results in reduced power dissipation.

This keeps the DRV102 and load cooler, resulting in in-

creased reliability for both devices. PWM frequency is a

constant 24kHz.

Resistor-Controlled Duty Cycle

Duty cycle is independently programmed with a resistor

ground. Increased resistor values correspond to decreased

duty cycles. Table II provides resistor values for typical duty

cycles. Resistor values for additional duty cycles can be

obtained from Figure 4. For reference purposes, the equation

DUTY CYCLE

10

536

3.67

20

137

3.31

30

66.5

2.91

40

39.2

2.49

50

24.9

2.07

60

16.2

1.66

70

10.5

1.26

80

6.65

0.88

90

4.42

0.56

NOTES: (1) Resistor values listed are nearest 1% standard values. (2) Do not

drive pin below 0.1V. For additional values, see “Duty Cycle vs Voltage” typical

performance curve.

Voltage-Controlled Duty Cycle

Duty cycle can also be programmed with an analog voltage,

this voltage results in decreased duty cycles. For 0% duty

values for typical duty cycles. See the “Duty Cycle vs

Voltage” typical performance curve for additional duty cycle

values.

The Duty Cycle Adjust pin should not be driven below 0.1V.

If the voltage source used can go between 0.1V and ground,

a 1k

Ω series resistor between the voltage source and the Duty

Cycle Adjust pin (Figure 5) is required to limit swing. If the

pin is driven below 0.1V, the output will be unpredictable.

The DRV102’s internal 24kHz oscillator sets the PWM

period. This frequency is not externally adjustable. Duty

Cycle Adjust (pin 3) is internally driven by a 200

µA current

source and connects to the input of a comparator and a 19k

Ω

resistor as shown in Figure 6. The DRV102’s PWM control

design is inherently monotonic. That is, a decreased voltage

(or resistor value) always produces an increased duty cycle.

10

20

40

60

100

80

Duty Cycle (%)

1000

100

10

1

R

R

DC = duty cycle in %

For 50% duty cycle:

= 24.9k

Ω