LTC1998
2.5µA, 1% Accurate
SOT-23 Comparator and Voltage
Reference for Battery Monitoring
FEATURES
s
s
s
s
s
s
s
DESCRIPTIO
High Accuracy Trip Voltage: 1% Max Error Using
External 1% Resistors
Adjustable Threshold Voltage and Hysteresis
Quiescent Current: 2.5µA Typ
Output Swings Rail-to-Rail
Thresholds Programmable from 2.5V to 3.25V
Output State Guaranteed for V
BATT
≥
1.5V
Low Profile (1mm) ThinSOT
TM
Package
The LTC
®
1998 is a micropower comparator and a preci-
sion adjustable reference in a 6-pin SOT-23 package that
is optimized for lithium-ion low battery detection circuits.
The LTC1998 features a voltage detection circuit with an
adjustable threshold voltage and hysteresis. The thresh-
old voltage can be programmed from 2.5V to 3.25V with
two external resistors. A 10mV to 750mV hysteresis can
be added with a third external resistor.
A proprietary internal architecture maintains 1% thresh-
old voltage accuracy over temperature with low cost 1%
external resistors.
A separate power supply pin, V
LOGIC
, allows the battery-
low logic output to operate below the battery voltage,
allowing compatibility with low voltage microprocessors
without a pull-up resistor. Power supply glitches are
eliminated by preventing the cross-conducting current
which occurs when the output changes state.
The LTC1998 operates with battery or supply voltages up
to 5.5V and its battery-low output is valid for battery
voltages above 1.5V.
APPLICATIO S
s
Lithium-Ion Battery-Powered Equipment
PDAs
Cell Phones
Handheld Instruments
Battery Packs
Pagers
Palm Top Computers
POS Terminals
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
BLOCK DIAGRA
Threshold Voltage Error vs Temperature
1.0
BATT
V
LOGIC
1.1R
V
HYST.A
V
TH.A
1.2V
% ERROR
THRESHOLD
ADJUST
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1998 BD
R
BATTLO
0
–45 –25
U
V
TH.A
SET BY 1%
EXTERNAL R,
THRESHOLD = 3V
V
TH.A
= 1V
THRESHOLD = 3V
V
TH.A
SHORTED
TO GROUND,
THRESHOLD = 2.5V
35
15
55
–5
TEMPERATURE (°C)
75
95
1998
G05
W
U
1998f
1
LTC1998
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
BATT 1
GND 2
V
TH.A
3
6 BATTLO
5 V
LOGIC
4 V
H.A
Total Supply Voltage (BATT or V
LOGIC
to GND) ......... 6V
Voltage
V
TH.A
, V
H.A ...........................
BATT + 0.3V to GND – 0.3V
BATTLO ........................ V
LOGIC
+ 0.3V to GND – 0.3V
Operating Temperature Range (Note 3) ...–40°C to 85°C
Specified Temperature Range (Note 4)
LTC1998C ...........................................–40°C to 85°C
LTC1998I .............................................–40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LTC1998CS6
LTC1998IS6
S6 PART MARKING*
LTTY
S6 PACKAGE
6-LEAD PLASTIC SOT-23
T
JMAX
= 150°C,
θ
JA
= 250°C/W
*The temperature grades are indentified by a label on the shipping container.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
GND
= 0V, unless otherwise noted.
PARAMETER
Power Supply
Supply Voltage Range-BATT
Supply Voltage Range-V
LOGIC
Supply Current, V
BATT
= 3V,
V
TH.A
= 1.5V
Supply Current, V
BATT
= 5.5V,
V
TH.A
= 1.5V
Monitor
Threshold Accuracy
V
BATT.Th
= 2.5V, Pin 3 Shorted to Ground
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
1.5
1
TYP
MAX
5.5
V
BATT
UNITS
V
V
µA
µA
µA
µA
µA
µA
%
%
%
%
%
%
%
%
%
%
mV
mV
mV
µs
µs
T
A
= 25°C
LTC1998CS6
LTC1998IS6
T
A
= 25°C
LTC1998CS6
LTC1998IS6
2.5
q
q
3.5
4.2
4.5
4.3
5.2
5.5
0.85
1
0.61
0.71
1
1.1
0.65
0.85
1.1
1.3
5
750
3
q
q
0.6
0.8
0.5
0.6
0.8
0.9
0.6
0.7
0.9
1
–5
10
350
150
±5
V
BATT.Th
= 3V, Pin 3 Driven by Precision
Voltage Source to 1V
V
BATT.Th
= 3V, V
TH.A
= 1V (Note 5)
Programmed with 1% Max External Resistors
V
BATT.Th
= 3.25V, Pin 3 Diven by Precision
Voltage Source to 1.5V
V
BATT.Th
= 3.25V, V
TH.A
= 1.5V (Note 5)
Programmed with1% Max External Resistors
Hysteresis Accuracy
Allowable Hysteresis Range (Note 2)
Propagation Delay
Threshold Adjust Pin Leakage, I
TH.A
Hysteresis Adjust Pin Leakage, I
H.A
Output
BATTLO High Voltage
BATTLO Low Voltage
BATTLO Low Voltage
I
OUT
= –1mA
I
OUT
= 1mA, V
BATT
≥
2V
I
OUT
= 0.25mA, V
BATT
= 1V
C
OUT
= 100pF, Overdrive = 10mV
Overdrive = 100mV
V
TH.A
≤
1.5V
V
H.A
≤
1.5V
V
HYST
≤
250mV
250mV
≤
V
HYST
≤
750mV
LTC1998C
LTC1998I
LTC1998C
LTC1998I
LTC1998C
LTC1998I
LTC1998C
LTC1998I
q
q
q
q
q
q
q
q
q
q
q
q
q
0.01
0.01
V
LOGIC
– 0.3
1
1
q
q
q
0.2
0.3
2
U
nA
nA
V
V
V
1998f
W
U
U
W W
W
LTC1998
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Maximum allowable hysteresis depends on desired trip voltages.
See application notes for details.
Note 3:
LTC1998C and LTC1998I are guaranteed functional over the
operating temperature range of – 40°C to 85°C.
Note 4:
The LTC1998C is guaranteed to meet specified performance from
0°C to 70°C. The LTC1998C is designed, characterized and expected to
meet specified performance from –40°C to 85°C but is not tested or QA
sampled at these temperatures. The LTC1998I is guaranteed to meet
specified performance from –40°C to 85°C.
Note 5:
This parameter is not 100% tested.
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Supply Current vs
Supply Voltage
3.5
3.0
T
A
= 25°C
V
LOGIC
= V
BATT
3.5
3.0
2.5
V
TH.A
= 1.5V
2.0
1.5
1.0
0.5
0
–50
2.5
2.0
1.5
1.0
0.5
V
TH.A
= 0V
THRESHOLD VOLTAGE (V)
SUPPLY CURRENT (µA)
SUPPLY CURRENT (µA)
V
TH.A
= 1.5V
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
1998 G01
Available Hysteresis vs
Threshold Voltage
750
1.0
0.9
AVAILABLE HYSTERESIS (mV)
0.8
500
% ERROR
0.7
0.6
0.5
0.4
0.3
0.2
0.1
V
TH.A
= 1V
THRESHOLD = 3V
V
TH.A
SET BY 1%
EXTERNAL R,
THRESHOLD = 3V
INPUT CURRENT V
TH.A
, V
H.A
(pA)
250
0
2.5
3.25
2.75
3.0
LOW BATTERY THRESHOLD VOLTAGE (V)
1998 G04
U W
Quiescent Supply Current vs
Temperature
V
BATT
= V
LOGIC
= 3V
Threshold Voltage vs Threshold
Adjust Voltage
3.5
3.0
2.5
–30
–10
10
30
50
TEMPERATURE (°C)
70
90
0
0.5
1.0
THRESHOLD ADJUST VOLTAGE (V)
1.5
1998 G02
1998 G03
Threshold Voltage Error vs
Temperature
10000
Input Current vs Temperature
V
IN
= 1.5V
1000
100
V
IN
= 1V
V
IN
= 0.5V
V
TH.A
SHORTED
TO GROUND,
THRESHOLD = 2.5V
10
1
0
–45 –25
35
15
55
–5
TEMPERATURE (°C)
75
95
0.1
35 45
55
65 75 85 95 105 115 125
TEMPERATURE (°C)
1998 G06
1998
G05
1998f
3
LTC1998
TYPICAL PERFOR A CE CHARACTERISTICS
Output Low Voltage vs Load
Current
OUTPUT VOLTAGE RELATIVE TO V
BATT
(mV)
0.6
T
A
= 25°C
V
LOGIC
= V
BATT
= 3V
0
T
A
= 85°C
T
A
= 25°C
T
A
= –40°C
OUTPUT VOLTAGE (V)
T
A
= 85°C
0.4
CURRENT (mA)
T
A
= 25°C
0.2
T
A
= –40°C
0
1
2
3
4
OUTPUT SINK CURRENT (mA)
5
1998 G07
PI FU CTIO S
BATT (Pin 1):
Battery Voltage to be monitored. Supply
current is also drawn from this pin. Board layout should
connect this pin to the battery(+) terminal, through a trace
that does not conduct load current.
GND (Pin 2):
Ground should be connected to the battery
(–) terminal through a trace that does not conduct load
return current.
V
TH.A
(Pin 3):
Threshold Adjust Pin. Adjusts the low
battery threshold voltage, V
BATT.Th
= 2.5V + (V
TH.A
/2).
V
TH.A
can be supplied by a voltage source or a resistor
divider.
V
H.A
(Pin 4):
Hysteresis Adjust. Hysteresis threshold
voltage V
TH2
= 2.5V + (V
H.A
/2). V
H.A
can be supplied by a
voltage source or resistor divider. V
H.A
must always be
programmed to a higher potential than V
TH.A
. Hysteresis
voltage, V
HYST
= V
TH2
– V
BATT.Th
.
V
LOGIC
(Pin 5):
Positive Supply Voltage for Output Driver.
This voltage can be driven from an external logic supply or
tied to BATT.
BATTLO (Pin 6):
Output of Comparator. Low for BATT <
V
BATT.Th
(low battery threshold voltage). Output state
guaranteed for V
BATT
≥
1.5V.
QUICK DESIG GUIDE
How to Calculate the External Resistor Values
The LTC1998 is a low battery warning indicator and is
especially designed for monitoring the voltage of single-
cell Lithium-Ion batteries. The LTC1998 compares its
supply pin (BATT) to an accurate internal reference; if the
battery voltage falls below the programmed low battery
threshold voltage of the LTC1998, the battery low pin
(BATTLO) will change state, from high to low, to indicate
a low battery condition. The low battery threshold voltage
is programmed via the voltage threshold adjust pin (V
TH.A
).
A hysteresis adjust pin (V
H.A
) will add hysteresis to the
programmed value of the low battery threshold voltage.
4
U W
Output High Voltage vs Load
Current
120
100
80
60
40
20
BATT = 3V
BATT = 5V
5
1998 G08
Output Short-Circuit Current vs
Supply Voltage
TA = 25°C
V
BATT
= V
LOGIC
–50
–100
T
A
= –40°C
T
A
= 25°C
T
A
= 85°C
SOURCE CURRENT,
BATTLO SHORTED TO GND
–150
–200
T
A
= 25°C
V
LOGIC
= V
BATT
1
–250
SINK CURRENT,
BATTLO SHORTED
TO V
LOGIC
2
3
4
OUTPUT SOURCE CURRENT (mA)
0
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
SUPPLY VOLTAGE (V)
1998 G09
U
U
U
U
1998f
LTC1998
QUICK DESIG GUIDE
Typical Application
Table 1: Design Equations for R1, R2, R3, Figure 1
Choose desired values for:
• V
BATT.Th
: Low Battery Threshold Voltage
• V
HYST
: Hysteresis Voltage
• I
R
: Max Allowable Resistor Current
Solve:
R
TOTAL
=
R1
+
R2
+
R3
=
5V
R1
=
R
TOTAL
•
– 1
V
BATT .Th
+
V
HYST
5V
– 1
– R1
R2
=
R
TOTAL
•
V
BATT .Th
R3
=
R
TOTAL
– R1 – R2
Li-Ion
APPLICATIO S I FOR ATIO
LOW BATTERY THRESHOLD VOLTAGE AND
HYSTERESIS ADJUST
Low Battery Threshold Voltage Adjustment, Pin 3
The low battery threshold voltage is the battery voltage
which will trip the (BATTLO) pin high to low. It should be
adjusted via the threshold adjust pin (V
TH.A
). This is a high
input impedance pin that senses an externally applied
voltage and programs the low battery threshold voltage
(V
BATT.Th
). The V
TH.A
pin is designed to accommodate
voltages from 0V to 1.5V with respect to ground. This
allows the low battery threshold voltage to be set to any
voltage between 2.5V and 3.25V, that is:
V
BATT .Th
=
2.5V
+
(V
TH.A
)
2
Li-Ion
U
W
U U
U
Example 1: A system using a 4.2V (fully charged) Lithium-
Ion battery requires a low battery threshold of 2.7V,
100mV hysteresis and can allow up to 4.2µA maximum
resistor current.
R
TOTAL
= 1MΩ, R1 = 786k, R2 = 66k and R3 = 148k
Choose standard 1% values.
R1 = 787k, R2 = 66.5k, R3 = 147k
1.5V TO 4.2V
REGULATOR
1
BATT
5
4
V
H.A
V
LOGIC
LTC1998
3
R3
1%
6
V
TH.A
BATTLO
GND
2
1998 F01
V
LOGIC
4.2V
I
R
+
R1
1%
R2
1%
0.1µF
µP
Figure 1. Low Battery Threshold Detector with Hysteresis
For instance, if the applied voltage at pin 3, V
TH.A
, is 1V the
LTC1998 will indicate a low battery condition when the
battery voltage pin (BATT) falls below 3V.
The voltage at the threshold adjust pin (V
TH.A
) can be set
with any voltage source. This pin allows a continuous time
adjustment, that is, the low battery threshold voltage may
be changed at any time. The high input impedance of the
V
TH.A
pin allows the use of a high valued resistive divider
(to minimize current drain) from the battery to set the
battery low threshold voltage, Figure 2.
+
R1
3
R2
1
BATT
V
TH.A
LTC1998
2
1998 F02
Figure 2. Resistor Divider Sets Threshold
1998f
5
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