Datasheet

23
LTC1285/LTC1288
TYPICAL APPLICATIONS N
U
39k
2.7V
LT1004-1.2
220k
39k
3Ω
BATTERY MONITOR 
INPUT 8V TO 16V
1µF
0.1µF
CS
CLK
D
OUT
LTC1285
LTC1285/88 • F15
–IN

V
CC
V
REF
GND
+IN
Figure 15. Micropower Battery Voltage Monitor
Figure 13. “Quick Look” Circuit for the LTC1285
A “Quick Look” Circuit for the LTC1285
Users can get a quick look at the function and timing of the
LT1285 by using the following simple circuit (Figure 13).
V
REF
is tied to V
CC
. V
IN
is applied to the +IN input and the
–IN input is tied to the ground. CS is driven at 1/16 the
clock rate by the 74C161 and D
OUT
outputs the data. The
output data from the D
OUT
pin can be viewed on an
oscilloscope that is set up to trigger on the falling edge of
CS (Figure 14). Note the LSB data is partially clocked out
before CS goes high.
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
Micropower Battery Voltage Monitor
A common problem in battery systems is battery voltage
monitoring. This circuit monitors the 10 cell stack of NiCad
or NiMH batteries found in laptop computers. It draws only
40µA from the 2.7V supply at f
SMPL
= 0.1kHz and 30µA to
62µA from the battery. The 12-bits of resolution of the
LTC1285 are positioned over the desired range of 8V to
16V. This is easily accomplished by using the ADC’s
differential inputs. Tying the –input to the reference gives
an ADC input span of V
REF
to 2V
REF
(1.2V to 2.4V). The
resistor divider then scales the input voltage for 8V to 16V.
CLR
CLK
A
B
C
D
P
GND
V
CC

RC
QA
QB
QC
QD
T
LOAD
74HC161
V
IN
TO OSCILLOSCOPE
CLOCK IN 120kHz
LTC1285/88 • F13
V
CC

CLK
D
OUT


LTC1285

+IN
–IN
GND
4.7µF
2.7V
V
REF
CS

MSB
(B11)
VERTICAL: 2V/DIV
HORIZONTAL: 20µs/DIV
LSB
(B0)
NULL
BIT
Figure 14. Scope Trace the LTC1285 “Quick Look” Circuit
Showing A/D Output 101010101010 (AAA
HEX
)