MAX17843 datasheet(81/131 Pages) MAXIM

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Cn Leakage Diagnostic

Leakage at the Cn inputs can cause the voltage seen by

the ADC to be different than that at the voltage source

due to the resistance of the external filter circuit. By utiliz-

ing an alternate measurement path, any voltage errors

as a result of Cn pin leakage can be detected. The SWn

pins are connected to the cell sources through an alter-

nate path. Implementing an HVMUX connection from

the SWn pins to the LSAMP completes the redundant

measurement path. This alternate measurement path

for the cell measurements can be enabled by setting the

ALTMUXSEL bit of the DIAGCFG register. When this bit

is set and a measurement cycle started, all cell measure-

ments are taken using the alternate path instead of the Cn

pin HVMUX connections. Measurements taken with the

normal and alternate paths can be compared and should

be nearly identical for a system with no faults. Since the

SWn pins typically have a smaller external filter time

constant than the Cn pins, increasing the oversampling

setting for this diagnostic measurement may be beneficial

for reducing measurement noise when the measurement

is taken while the cells are exposed to transient loads.

Cell Overvoltage Diagnostic

Enabling balancing switches can be used to generate a

voltage up to 2 x VCELL at the ALTMUX inputs to test the

input-range capability, assuming the cell is sufficiently

charged.

A cell-position input voltage is elevated by approximately

1.5 x VCELLn turning on either BALSWn+1 or BALSWn-1.

When the adjacent switch is turned on, the SWn pin

shared with the switch is moved by 0.5 x VCELL, which

causes VCELLn to increase by that amount when mea-

sured with the ALTMUX path. For the topmost cell posi-

tion, BALSWn-1 must be used, and for the bottom cell

position, BALSWn+1 must be used. By turning on two

adjacent switches instead of one, such as BALSWn+1

and BALSWn+2, the measured voltage is approximately

2 x VCELL, assuming all cells are at approximately the

same voltage. This technique can create an input voltage

that exceeds the overvoltage threshold to verify the higher

end of the input range and the overvoltage alert function.

Input range can also be verified by using the cell-test

sources to induce a higher cell-channel voltage. If the

change is as expected, it shows that the system can mea-

sure voltages above the present nominal input voltage.

Figure 52. Redundant HVMUX Paths

LSAMP

ADC

HVMUX

BUS

HVMUX

BUS

ALTMUX

BUS

ALTMUX

BUS

RFILTER

RBALANCE

CELL n

RFILTER

RBALANCE

CFILTER

RBAL

FILTER

TO CELL n-1

TO CELL n+1

SENSE

WIRE

SENSE

WIRE

CFILTER

SWn

SWn-1

Cn-1

AGND

MAX17843

12-Channel, High-Voltage Smart Sensor

Data-Acquisition Interface

www.maximintegrated.com

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