LTC6801HG-TRPBF(RevC) データシートの表示（PDF） - Linear Technology

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LTC6801HG-TRPBF
(Rev.:RevC)

Independent Multicell Battery Stack Fault Monitor

Linear Technology 

LTC6801

APPLICATIONS INFORMATION

READING EXTERNAL TEMPERATURE PROBES

The LTC6801 includes two channels of ADC input, VTEMP1

and VTEMP2, that are intended to monitor thermistors

(tempco about –4%/°C generally) or diodes (–2.2mV/°C

typical) located within the cell array. Sensors can be

powered directly from VREF as shown in Figure 9 (up to

30µA typical).

The temperature measurement inputs (VTEMP1, VTEMP2) of

the LTC6801 are comparator input channels with a voltage

threshold of one-half VREF. Input voltages above half VREF

are considered good. Voltages below the one-half VREF

threshold are considered a fault condition. The inputs

may be used in combination with resistors, thermistors,

or diodes to sense both an upper and lower temperature

limit. Figure 9, Figure 10 and Figure 11 illustrate some

possibilities. To ignore these inputs simply connect VTEMP1

and VTEMP2 to VREF. A filtering capacitor to V– is recom-

mended to minimize the error caused by the approximately

700k input impedance of the ADC.

For sensors that require higher drive currents, a buffer

amplifier may be used as shown in Figure 10. Power for

the sensor is actually sourced indirectly from the VREG pin

in this case. Probe loads up to about 1mA maximum are

supported in this configuration. Since VREF is shut down

while the LTC6801 is idle between measurement cycles,

the thermistor drive is also shut off and thus power dis-

sipation is minimized. Since VREG remains always-on, the

buffer op amp (LT6003 shown) is selected for its ultralow

current consumption (10µA).

500k

NTC

B = 4567

100k

1150k

1µF

1µF

100k

NTC

B = 4250

V+

OV1

C12

OV0

C11

UV1

C10

UV0

C9

HYST

C8

CC1

C7 LTC6801 CC0

C6

SLT

C5

SLTOK

C4

DC

C3

EOUT

C2

EOUT

C1

SIN

V–

SIN

VTEMP1

SOUT

VTEMP2

SOUT

VREF

EIN

VREG

EIN

6801 F11

Figure 11. Sensing Both Upper and Lower Temperature

Thresholds. This Example Monitors a –20°C to +60°C Window

Detector. The Thermistors Should Be in Close Proximity

For circuits that include filtering capacitance, note that

only the fastest DC setting (VREG connection) will keep

VREF steady and allow the VTEMP voltages to settle. To use

the lower power DC settings, VREF must be buffered (see

Figure 10), so that a low impedance is presented to the

ADC, with a time constant of no more than about 1ms.

ADVANTAGES OF DELTA-SIGMA ADCs

The LTC6801 employs a delta-sigma analog to digital

converter for voltage measurement. The architecture of

delta-sigma converters can vary considerably, but the

common characteristic is that the input is sampled many

times over the course of a conversion and then filtered or

averaged to produce the digital output code.

For more information www.linear.com/LTC6801

6801fc

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