LTC6906 datasheet(20/28 Pages) AD

20 / 28 page

LTC6994-1/LTC6994-2

Rev. C

For more information www.analog.com

Power Supply Current

The Electrical Characteristics table specifies the supply

current while the part is idle (waiting for an input transi-

tion). IS(IDLE) varies with the programmed tDELAY and the

supply voltage, as described by the equations in Table 2,

valid for both the LTC6994-1 and LTC6994-2.

Table 2. Approximate Idle Supply Current Equations

CONDITION

TYPICAL IS(IDLE)

NDIV ≤ 64

V + • NDIV • 7pF + 4pF

(

)

tDELAY

V +

500kΩ

+ 2.2 •ISET + 50µA

NDIV ≥ 512

V + •NDIV • 7pF

tDELAY

V +

500kΩ

+ 1.8 •ISET + 50µA

When an input transition starts the delay timing circuity,

the instantaneous supply current increases to IS(ACTIVE).

IS(ACTIVE) = IS(IDLE) + ∆IS(ACTIVE)

APPLICATIONS INFORMATION

∆IS(ACTIVE)canbeestimatedusingtheequationsinTable 3,

assuming a periodic input with frequency fIN. The equa-

tions assume the input pulse width is greater than tDELAY;

otherwise, the output will not transition (and the increase

in supply current will be less).

Table 3. Active Increase in Supply Current

CONDITION

DEVICE

TYPICAL ∆IS(ACTIVE)*

NDIV ≤ 64

LTC6994-1

fIN • V+ • (NDIV • 5pF + 18pF + CLOAD)

LTC6994-2

fIN • V+ • (NDIV • 10pF + 22pF + CLOAD)

NDIV ≥ 512 Either Version

fIN • V+ • CLOAD

*Ignoring resistive loads (assumes RLOAD = ∞)

Figures 14 and 15 show how the supply current increases

from IS(IDLE) as the input frequency increases. At higher

NDIV settings, the increase in active current is smaller.

fIN • tDELAY

“IDLE”

150

200

250

0.8

699412 F14

100

0.2

0.4

0.6

1.0

÷1, RSET = 50k

÷8, RSET = 50k

÷1, RSET = 100k

÷1, RSET = 800k

V+ = 3.3V

INPUT PULSE WIDTH = 1.1 • tDELAY

CLOAD = 5pF

RLOAD = ∞

fIN • tDELAY

“IDLE”

150

200

250

0.4

699412 F15

100

0.1

0.2

0.3

0.5

÷1, RSET = 50k

÷8, RSET = 50k

÷1, RSET = 100k

÷1, RSET = 800k

V+ = 3.3V

fIN < 1/(2 • tDELAY) TO ALLOW RISING AND

FALLING DELAYS TO REACH THE OUTPUT

CLOAD = 5pF

RLOAD = ∞

Figure 14. IS(ACTIVE) vs Input Frequency, LTC6994-1

Figure 15. IS(ACTIVE) vs Input Frequency, LTC6994-2

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