LTC6907HS6 View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

LTC6907HS6

Micropower, 40kHz to 4MHz Resistor Set Oscillator in SOT-23

Linear Technology 

LTC6907

APPLICATIO S I FOR ATIO

1000

CLOAD = 5pF

T = 25°C

3.3V, –: 1

3.3V, –: 3

3.3V, –: 10

100

10

10

100

1000

OUTPUT FREQUENCY (kHz)

10000

6907 F09

Figure 9. Supply Current vs Frequency over DIV Settings

layout that uses the GRD pin and a “guard ring” to absorb

leakage currents. The guard ring surrounds the SET pin

and the end of RSET to which it is connected. The guard ring

must have no solder mask covering it to be effective. The

GRD pin voltage is held within a few millivolts of the SET

pin voltage, so any leakage path between the SET pin and

the guard ring generates no leakage current.

Start-Up Time

When the LTC6907 is powered up, it holds the OUT pin

low. After the master oscillator has settled, the OUT pin is

enabled and the first output cycle is accurate. The time

from power-up to the first output transition is given

approximately by:

tSTART ≅ 64 • tOSC + 100µs

The digital divider ratio, N, does not affect the start-

up time.

LTC6907

1 OUT

V+ 6

GRD

2 GND

5

3 DIV

RSET

SET 4

NO SOLDER MASK

OVER THE GUARD RING

GUARD

RING

NO LEAKAGE

CURRENT

6907 F10

LEAKAGE

CURRENT

Figure 10. PC Board Layout with Guard Ring

Power Supply Rejection

The LTC6907 has a very low supply voltage coefficient,

meaning that the output frequency is nearly insensitive to

the DC power supply voltage. In most cases, this error

term can be neglected.

High frequency noise on the power supply (V+) pin has the

potential to interfere with the LTC6907’s master oscillator.

Periodic noise, such as that generated by a switching

power supply, can shift the output frequency or increase

jitter. The risk increases when the fundamental frequency

or harmonics of the noise fall near the master oscillator

frequency. It is relatively easy to filter the LTC6907 power

supply because of the very low supply current. For ex-

ample, an RC filter with R = 160Ω and C = 10µF provides

a 100Hz lowpass filter while dropping the supply voltage

only about 10mV.

Operating the LTC6907 with Supplies Higher

Than 3.6V

The LTC6907 may also be used with supply voltages

between 3.6V and 5.5V under very specific conditions. To

ensure proper functioning above 3.6V, a filter circuit must

be attached to the power supply and located within 1cm of

the device. A simple RC filter consisting of a 100Ω resistor

and 1µF capacitor (Figure 11) will ensure that supply

resonance at higher supply voltages does not induce

unpredictable oscillator behavior. Accuracy under higher

supplies may be estimated from the typical Frequency vs

Supply Voltage curves in the Typical Performance Charac-

teristics section of this data sheet.

V+

3.6V TO 5.5V DC

100Ω

1µF

LTC6907

V+ OUT

GND GRD

DIV SET

RSET

6907 F11

Figure 11. Using the LTC6907 at Higher Supply Voltages

6907fa

9

Share Link: