TS3003

Page 8

TS3003 Rev. 1.0

Ω, the output frequency is

approximately 25kHz with a 50% duty cycle. As

design aids, Tables 1 lists TS3003’s typical FOUT for

The output frequency can be user-adjusted from

9kHz to 300kHz with a single resistor. The TS3003

also provides a separate PWM output signal at its

PWMOUT terminal that is anti-phase with respect to

FOUT. A dead time of approximately 106ns exists

between FOUT and PWMOUT. To adjust the pulse

width of the PWMOUT output, a single capacitor can

be placed at the CPWM pin. To determine the

capacitance needed for a desired pulse width, the

following equation is to be used:

CPWM(F)=

Equation 2. CPWM Capacitor Calculation

voltage applied to the CPWM capacitor, respectively.

The pulse width is determined based on the period of

FOUT and should never be greater than the period at

FOUT. Make sure the PWM_CNTRL pin is set to at

least 400mV when calculating the pulse width of

approximately 1µA.

The PWMOUT output pulse width can be adjusted

further after selecting a CPWM capacitor. This can be

achieved by applying a voltage to the PWM_CNTRL

2. For example, with a period of 40µs( 25kHz) a 47pF

capacitor at the CPWM pin generates a pulse width

of approximately 16µs. This can be calculated using

equation 2. By reducing the PWM_CNTRL voltage

≅ 300mV to GND, the pulse width is

reduced from 16µs to approximately 8µs. This is a

pulse width reduction of 50%. Note that as the FOUT

frequency increases, the amount of pulse width

reduction reduces and vice versa. Furthermore, if the

PWMOUT output is half the frequency of the FOUT

output, this means your CPWM capacitor is too large

and as a result, the pulse width is greater than the

FOUT period. In this case, use Equation 2 and

reduce the capacitor value to less than the period.

Connect CPWM to VDD to disable the PWM function

and in turn, save power. Connect PWM_CNTRL to

VDD for a fixed PWMOUT output pulse width, which

is determined by the CPWM pin capacitor only.

APPLICATIONS INFORMATION

Minimizing Power Consumption

To keep the TS3003’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

TS3003’s transient power consumption and, as well,

should be as small as possible.

One challenge to minimizing the TS3003’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 TS3003’s FOUT

and PWMOUT terminals.

probe capacitance is known by simply solving for

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

be

≤7.5pF.

Figure 1: Using an External Capacitor in Series with

Probes Reduces Effective Capacitive Load.

1

1

-

1

Equation 3:External Capacitor Calculation