LTC2914IGN-2 datasheet(12/16 Pages) LINER

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LTC2914

2914f

At VCC = 1V, the weak pull-up current on OV is barely turned

on. Therefore, an external pull-up resistor of no more than

100k is recommended on the OV pin if the state and pull-up

strength of the OV pin is crucial at very low VCC.

Note however, by adding an external pull-up resistor, the

pull-up strength on the OV pin is increased. Therefore, if

it is connected in a wired-OR connection, the pull-down

strength of any single device must accommodate this

additional pull-up strength.

Output Rise and Fall Time Estimation

The UV and OV outputs have strong pull-down capabil-

ity. The following formula estimates the output fall time

(90% to 10%) for a particular external load capacitance

(CLOAD):

tFALL ≈ 2.2 • RPD • CLOAD

where RPD is the on-resistance of the internal pull-down

transistor, typically 50

Ω at VCC > 1V and at room tem-

perature (25°C). CLOAD is the external load capacitance

on the pin. Assuming a 150pF load capacitance, the fall

time is 16.5ns.

The rise time on the UV and OV pins is limited by a 400k

pull-up resistance to VCC. A similar formula estimates the

output rise time (10% to 90%) at the UV and OV pins:

tRISE ≈ 2.2 • RPU • CLOAD

where RPU is the pull-up resistance.

APPLICATIO S I FOR ATIO

OV Latch (LTC2914-1)

With the LATCH pin held low, the OV pin latches low when

an OV condition is detected. The latch is cleared by raising

the LATCH pin high. If an OV condition clears while LATCH

is held high, the latch is bypassed and the OV pin behaves

the same as the UV pin with a similar timeout period at the

output. If LATCH is pulled low while the timeout period is

active, the OV pin latches as before.

Disable (LTC2914-2)

The LTC2914-2 allows disabling the UV and OV outputs

via the DIS pin. Pulling DIS high forces both outputs to

remain weakly pulled high, regardless of any faults that

occur on the inputs. However, if a UVLO condition oc-

curs, UV asserts and pulls low, but the timeout function

is bypassed. UV pulls high as soon as the UVLO condition

is cleared.

DIS has a weak 2µA (typical) internal pull-down current

guaranteeing normal operation with the pin left open.

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