TS3002 datasheet(9/11 Pages) TOUCHSTONE

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TS3002

TS3002DS r1p0

Page 9

RTFDS

the CNTRL both enables the TS3002’s internal PWM

engine as well as adjusting the duty cycle from 12%

to 90%. A dc control voltage equal to 0.03 x VDD

applied to the CNTRL pin enables the PWM engine

to set the duty cycle to 12%. A dc control voltage

equal to 0.27 x VDD increases the duty cycle to 90%

and connecting CNTRL to VDD disables the PWM

engine altogether. Configured for nominal operation

(PWM engine OFF, BOOST pin to GND), the supply

current of the TS3002 is 1µA; enabling the PWM

engine increases the TS3002 operating supply

current as shown in the electrical specification table.

The BOOST pin controls the propagation delay of the

TS3002’s internal comparators. When BOOST is

nnected

GND,

the

TS3002’s

maximum

programmable

operating

frequency

~90kHz.

Connecting the BOOST pin to VDD reduces the

propagation delay of the internal oscillators, thereby

extending

the

high

end

maximum

operating

frequency to 290kHz.

APPLICATIONS INFORMATION

Minimizing Power Consumption

To keep the TS3002’s power consumption low,

resistive loads at the FOUT and PWMOUT terminals

increase dc power consumption and therefore should

be as large as possible. Capacitive loads at the

FOUT

and

PWMOUT

terminals

increase

the

TS3002’s transient power consumption and, as well,

should be as small as possible.

One challenge to minimizing the TS3002’s transient

power consumption is the probe capacitance of

oscilloscopes and frequency counter instruments.

Most instruments exhibit an input capacitance of

15pF or more. Unless buffered, the increase in

transient load current can be as much as 400nA.

To minimize capacitive loading, the technique shown

in Figure 1 can be used. In this circuit, the principle of

series-connected capacitors can be used to reduce

the effective capacitive load at the TS3002’s FOUT

and PWMOUT terminals.

To determine the optimal value for CEXT once the

probe capacitance is known by simply solving for

CEXT using the following expression:

CE T =

CLOAD(EFF)

CPROBE

For example, if the instrument’s input probe

capacitance is 15pF and the desired effective load

capacitance at either or both FOUT and PWMOUT

terminals is to be

≤5pF, then the value of C

EXT should

≤7.5pF.

TS3002 Start-up Time

As the TS3002 is powered up, its FOUT terminal

(and PWMOUT terminal, if enabled) is active once

the applied VDD is higher than 0.9 volt. Once the

applied VDD is higher than 0.9 volt, the master

oscillator

achieves

steady-state operation

within

1.2ms.

Current- and Voltage-Controlled Oscillators

The TS3002 can be configured into a Current-

Controlled Oscillator as shown in Figure 2. With a

current source sourcing a current of 223nA to 262nA,

FOUT can generate an output signal with a frequency

range of 5.2kHz to 90kHz. In a similar manner, a

Voltage-Controlled Oscillator can be configured as

shown in Figure 3. In this case, a voltage source

sourcing a voltage of 290mV to 341mV can generate

an FOUT output signal frequency range of 5.2kHz to

90kHz as well. It is recommended to use resistor

values with a 1% tolerance.

Figure 1: Using an External Capacitor in Series with

Probes Reduces Effective Capacitive Load.

Figure 2: Configuring the TS3002 into a

Current-Controlled Oscillator.

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