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LTC6801

6801p

Self Test Pins

The SLT pin is used to initiate a self test. It is conﬁgured

as an open collector input/output. The pin should be nor-

mally tied to VREG with a resistor greater than or equal to

100k or ﬂoated. The pin may be pulled low at any time to

initiate a self test cycle.

The device will automatically initiate a self test if SLT has

not been externally activated for 1024 measurement cycles,

and pull down the SLT pin internally to indicate that it is

in self test mode.

The SLTOK pin is a simple logic output. If the previous self

test failed the output is held low, otherwise the output will

be high. The SLTOK pin is high upon power-up. The SLTOK

output can be connected to a microcontroller through an

isolation path.

The LTC6801 status output will remain active while the

SLTOK pin is low. The LTC6801 will continue to monitor

cells if the self test fails. If the next self test passes, the

SLTOK output returns high.

Reference and Comparator Veriﬁcation

A secondary internal bandgap voltage reference (REF2)

is included in the LTC6801 to aid in veriﬁcation of the

reference and comparator. During the self test cycle, the

comparator and main reference are used to measure the

REF2 voltage.

To verify the comparator functionality, the upper and

lower thresholds are ﬁrst set in a close window around

the expected REF2 voltage and the comparator output is

veriﬁed. Then the upper threshold is set below the REF2

voltage and the comparator output is veriﬁed again. Lastly,

the lower threshold is set above the REF2 voltage and the

comparator output is veriﬁed a third time.

The self test guarantees that VREF is within 5% of the

speciﬁed nominal value. Also, this test guarantees the

analog portion of the ADC is working.

High Voltage Multiplexer Veriﬁcation

The most dangerous failure mode of the high voltage

multiplexer would be a stuck bit condition in the address

decoder. Such a fault would cause some channels to be

measured repeatedly while other channels are skipped.

A skipped channel could mean a bad cell reading is not

detectable. Other multiplexer failures, like the simultaneous

selection of multiple channels, or shorts in the signal path,

would result in an undervoltage or overvoltage condition

on at least one of the channels.

The LTC6801 incorporates circuitry to ensure that

all requested channels are measured during each

measurement cycle and none are skipped. If a channel is

skipped, an error is ﬂagged during the self test cycle.

ADC Decimation Filter Veriﬁcation

The ADC decimation ﬁlter test veriﬁes that the digital cir-

cuits in the ADC are working, i.e. there are no stuck bits

in the ADC output register. During each self test cycle,

the LTC6801 feeds two test waveforms into the ADC. The

internally generated waveforms were designed to generate

complementary zebra patterns (alternating 0’s and 1’s) at

the ADC output. If either of the waveforms generates an

incorrect output value, an error is ﬂagged during the self

test cycle.

Open Cell Connection Detection

The open connection detection algorithm ensures that an

open circuit is not misinterpreted as a valid cell reading.

APPLICATIONS INFORMATION

LTC6801 Datasheet(PDF) 18 Page - Linear Technology

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