LTC6907 datasheet(11/24 Pages) AD

11 / 24 page

LTC6991

Rev. D

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OPERATION

RST Pin and Polarity (POL) Bit

The RST pin controls the state of the LTC6991’s output

as seen on the OUT pin. The active/inactive voltage levels

depend on the POL bit setting.

Table 2. Output States

POL BIT

RST PIN

OUTPUT STATE

Oscillating

0 (reset)

1 (reset)

Oscillating

Each period of the LTC6991’s internal oscillator clocks

the output state latch (see Block Diagram). The reset pin

(RST) can reset or hold off the output latch. The active

state of the reset pin is determined by the polarity func-

tion (POL). Similarly, the output latch is followed by a

buffer that can invert the output. The output polarity is

also controlled by the POL bit.

If POL = 0, the reset pin is active high and the output latch

is not inverted. Therefore, pulling the RST pin high will

reset the output latch and force the OUT pin low. Pulling

RST low will allow the output to oscillate, with the next

rising edge dependent on the internal oscillator.

If POL = 1, the reset pin is active low and the output latch

is inverted. Therefore, pulling the RST pin low will reset

the output latch and force the OUT pin high. Pulling RST

high will allow the output to oscillate, with the next falling

edge dependent on the internal oscillator.

Note that the master oscillator frequency and phase are

not affected by the RST pin; The LTC6991 continues to

oscillate, internally, even when RST is active. While the

reset function can block an output pulse, its exact place-

ment in time can only be changed by power cycling the

LTC6991.

tOUT

RST

OUT

tRST

tWIDTH

INTERNAL

OSCILLATOR

6991 F03

tOUT

RST

OUT

tRST

INTERNAL

OSCILLATOR

6991 F04

Figure 3. RST Timing Diagram (POL = 0)

Figure 4. RST Timing Diagram (POL = 1)

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