NCP45491

www.onsemi.com

9

AUXILIARY FUNCTIONS

Bus Comparator (BS_OK)

measured on the BS_INx pins) are valid is provided on the

BS_OK pin. BS_OK remains low until all used BS_INx

pins are above a user−defined threshold voltage. The

threshold voltage for the valid condition of BS_INx pins is

set by the voltage provided to the BS_REF pin and must be

less than 0.2 V. This can be done via an external resistor

divider and the bandgap reference. If desired, the user can

use the SKIP pin to modify the logic as shown in the

corresponding table (H=high, L=low, Z=tristate, X=don’t

care). The SKIP pin can also be used to hold BS_OK = L in

the absence of VCC.

Reset/Timeout

Normal operation can be interrupted and device returned

to standby mode by holding the MUX_SEL pin HIGH or

Bandgap Reference

The BG_REF_OUT pin provides a high−accuracy

voltage from which BS_REF and CM_REF_IN voltages

can be supplied via external voltage dividers.

Ground FET

The GND_FET pin is a switch that connects the bus

voltage dividers to ground. In order that these voltage

dividers not consume current when not needed (as in device

shutdown), a low−impedance open−drain FET disconnects

the low−side of these resistor dividers when the EN pin is at

a logic HIGH level.

Enable Function

The EN pin controls device operation according to the

corresponding table.

Mode Select Function

The MODE_SEL pin controls multiplexer operation

according

to

the

corresponding

table.

Note

that

MODE_SEL is left floating in stand−alone operation.

Reduced Channel Count

If an application requires less than 4 channels, then pins

for unused channels must be connected in the following

manner for correct operation of the BS_OK output.

PINS for Unused Channels

Connection

BS_INx

Connect to BS_IN pin of

previous channel

SH_Ox

Float

SH_IN_Px

Connect to VCC voltage or

higher

SH_IN_Nx

Connect to VCC voltage or

higher

Note: “x” refers to the unused channel number

Connecting the SH_IN_Px and SH_IN_Nx pins for

unused channels to the respective SH_IN_Px and

SH_IN_Nx of previous active channels is an acceptable way

to provide the bias voltages needed. If the SH_Ox pin is left

floating, then that channel and all subsequent channels will

be skipped in the DIFF_OUT readout. For example, if

SH_O3 is left floating, SH_O3 and SH_O4 will be

bypassed. If devices are in paired mode, the number of

unused channels on both devices must be matched.

However, bus voltage on those unused channels (as

measured on the BS_INx pins) will still be compared to the

BS_REF voltage and included in the BS_OK output logic.

If SKIP = 0 V, then the BS_INx voltages are ignored. In this

case the unused BS_INx pins can be tied to any voltage less

than VCC.

SKIP Logic

EN

VCC

BS_INx

SKIP

BS_OK

X

Z(unpowered)

X

H

L

X

L (POR)

X

X

L

H

X

X

X

L

Z/L

H

L

H

L

Z/L

H

H

H

H (open drain)

Z/L

H

X

L

H (open drain)

EN Logic

Level

Device Operation

LOW

Fully Functional

Tri−state

(floating)

Limited Function: BG_REF_OUT is valid,

GND_FET is turned ON, BS_OK comparators

and output are functional. All other functions to

be disabled. DIFF_OUT to be Hi−Z and multi-

plexer select logic is held in reset.

HIGH

Standby: As described in Limited Function

above with GND_FET turned OFF

MODE_SEL Logic

Level

Multiplexer Operation

LOW

Device A

Tri−state (floating)

Stand−Alone

HIGH

Device B