ADM2914 datasheet(12/16 Pages) AD

12 / 16 page

ADM2914

Rev. 0 | Page 12 of 16

UV AND

The

OV RISE AND FALL TIMES

UV and

)

)(

(

LOAD

PULL

−

≈

OV output rise times (from 10% to 90%) can be

approximated using the following formula:

where:

RPULL-UP is the internal weak pull-up resistance with an approx-

imate value of 400 kΩ at room temperature with VCC > 1 V.

CLOAD is the external load capacitance on the output pin.

When a fault occurs, the UV or

)

)(

(

LOAD

DOWN

PULL

−

≈

OV output fall time can be

expressed as

where RPULL-DOWN is the internal pull-down resistance, which is

approximately 50 Ω. Assuming a load capacitance of 150 pF, the

fall time is 16.5 ns.

UV/

Both the

OV OUTPUT CHARACTERISTICS

OV and UV outputs have a strong pull-down to

ground and a weak internal pull-up to VCC. This permits the pins

to behave as open-drain outputs. When the rise time on the pin

is not critical, the weak pull-up removes the requirement for an

external pull-up resistor. The open-drain configuration allows

for wire-OR’ing of outputs, which is particularly useful when

more than one signal needs to pull down on the output.

At VCC = 1 V, a maximum VOL = 0.15 V at UV is guaranteed. At

VCC = 1 V, the weak pull-up current on OV is almost turned on.

Consequently, if the state and pull-up strength of the OV pin are

important at very low VCC, an external pull-up resistor of no more

than 100 kΩ is advised. By adding an external pull-up resistor,

the pull-up strength on the

GLITCH IMMUNITY

OV pin is greater. Therefore, if it is

connected in a wire-OR’ed configuration, the pull-down strength

of any single device must account for this additional pull-up

strength.

The ADM2914 is immune to short transients that may occur

on the monitored voltage rails. The device contains internal

filtering circuitry that provides immunity to fast transient

glitches. Figure 9 illustrates glitch immunity performance by

showing the maximum transient duration without causing a

reset pulse. Glitch immunity makes the ADM2914 suitable for

use in noisy environments.

UNDERVOLTAGE LOCKOUT (UVLO)

The ADM2914 has an undervoltage lockout circuit that monitors

the voltage on the VCC pin. When the voltage on VCC drops

below 1.9 V (minimum), the circuit is activated. The UV output

is asserted and the OV output is cleared and not allowed to

assert. When VCC recovers, UV

SHUNT REGULATOR

exhibits the same timing

characteristics as if an undervoltage condition had occurred on

the inputs.

The ADM2914 is powered via the VCC pin. The VCC pin can be

directly connected to a voltage rail of up to 6 V. In this mode,

the supply current of the device does not exceed 100 µA. An

internal shunt regulator allows the ADM2914 to operate at

higher input voltage levels by placing a shunt resistor in series

between the supply rail and the VCC pin to limit the input current

to less than 10 mA. Use Figure 7 in the Typical Performance

Characteristics section to assist in determining the value of

this resistance. Choose an appropriate location on the curve to

accommodate variations in VCC due to changes in current through

the dropper resistor.

If an overvoltage condition occurs when the

LATCH (ADM2914-1)

LATCH pin is

pulled low, the OV pin latches low. Pulling LATCH high clears

the latch. If an OV condition clears while LATCH is high, the

latch is bypassed and the OV pin behaves in the same way as the

UV pin, with an identical timeout period. If the LATCH pin is

pulled low while the timeout period is active, the OV

DISABLE (ADM2914-2)

latches low, as in normal operation.

Pulling the DIS pin high disables both the UV and OV outputs,

and forces both outputs to remain weakly pulled high, regard-

less of any faults that are detected at the inputs. If a UVLO

condition is detected, the UV output is asserted and pulls low;

however, the timeout function is bypassed. As soon as the

UVLO condition clears, the UV output pulls high. To guarantee

normal operation when the pin is left unconnected, DIS has a

weak 2 µA internal pull-down current.

ADM2914 Fiches technique(PDF) 12 Page - Analog Devices

ADM2914 Fiches technique(HTML) 12 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Fiches technique Télécharger

Lien URL