参数资料
型号: LTC6801IG#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 电源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PDSO36
封装: LEAD FREE, PLASTIC, SSOP-36
文件页数: 14/28页
文件大小: 265K
代理商: LTC6801IG#TRPBF
LTC6801
21
6801fb
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 ltering capacitor to Vis 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
amplier 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 conguration. 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).
For circuits that include ltering 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 ltered or
averaged to produce the digital output code.
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
100k
500k
NTC
B = 4567
100k
NTC
B = 4250
1150k
1μF
V+
C12
C11
C10
C9
C8
C7
C6
C5
C4
C3
C2
C1
V–
VTEMP1
VTEMP2
VREF
VREG
OV1
OV0
UV1
UV0
HYST
CC1
CC0
SLT
SLTOK
DC
EOUT
SIN
SOUT
EIN
LTC6801
6801 F11
1μF
APPLICATIONS INFORMATION
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