LTC4071
applicaTions inForMaTion
dissipation, PD (in W), and
θ
JA
is the thermal impedance
of the package (in °C/W):
T
J
= T
A
+ (PD
× θ
JA
).
The application shown in Figure 4 illustrates how to prevent
triggering the low-battery disconnect function under large
pulsed loads due to the high ESR of thin-film batteries.
V
IN
FLOAT
R
IN
ADJ V
CC
BAT
NTCBIAS
LTC4071
NTC
GND
LBSEL
T
C
BYPASS
10k
PULSED
I
LOAD
SYSTEM LOAD
age recovers, as the capacity of the battery should provide
roughly 50 hours of use for an equivalent 0.1%•20mA =
20µA load. To prevent load pulses from tripping the low
battery disconnect, add a decoupling capacitor from V
CC
to
GND. The size of this capacitor can be calculated based on
how much margin is required from the LBD threshold as
well as the amplitude and pulse width of the load transient.
For a 1.0mAh battery with a state-of-charge of 3.8V, the
margin from LBD is 600mV with LBSEL tied to GND. For
a square-wave load pulse of 20mA with a pulse width of
5ms, the minimum size of the decoupling cap required to
hold V
CC
above LBD is calculated as follows:
C
BYPASS
=
20mA • 5ms
=
166.6µF
600mV
+
Li-Ion
4071 F04
NTHS0402N02N1002F
Take care to select a bypass capacitor with low leakage.
The LTC4071 can be used to charge a battery to a 4.2V
float voltage from an AC line with a bridge rectifier as
shown in the simple schematic in Figure 5. In this example,
DANGER! HIGH VOLTAGE
R1 = 249k
R2 = 249k
Figure 4. Adding a Decoupling Capacitor
for Large Load Transients
Table 2 lists some thin-film batteries, their capacities
and their equivalent series resistance. The ESR causes
V
BAT
and V
CC
to droop as a product of the load current
amplitude multiplied by the ESR. This droop may trigger
the low-battery disconnect while the battery itself may
still have ample capacity. Adding a bypass capacitor to
V
CC
prevents large low duty cycle load transients from
pulling down on V
CC
.
Table 2. Low Capacity Li-Ion and Thin-Film Batteries
VENDOR
CYMBET
CYMBET
GS NanoTech
APS-Autec
APS-Autec
IPS
IPS
IPS
IPS
GM Battery
P/N
CBC012
CBC050
N/A
LIR2025
LIR1025
MEC225-1P
MEC220-4P
MEC201-10P
MEC202-25P
GMB031009
CAPACITY
12µAh
50µAh
500µAh
20mAh
6mAh
0.13mAh
0.4mAh
1.0mAh
2.5mAh
8mAh
RESISTANCE
5k to 10k
1500Ω to 3k
40Ω
0.75Ω
30Ω
210Ω to 260Ω
100Ω to 120Ω
34Ω to 45Ω
15Ω to 20Ω
10Ω to 20Ω
V
MIN
3.0V
3.0V
3.0V
3.0V
2.75V
2.1V
2.1V
2.1V
2.1V
2.75V
AC 110V
MB4S
R3 = 249k
R4 = 249k
–
V
CC
+
SYSTEM
LOAD
NTC ADJ
LTC4071
FLOAT
NTCBIAS
LBSEL
BAT
GND
+
Li-Ion
4071 F05
BATTERY
For example, given a 0.1% duty cycle 5ms load pulse of
20mA and a 1.0mAh IPS MEC201-10P solid-state thin-film
battery with an equivalent series resistance of 35Ω, the
voltage drop at V
CC
can be as high as 0.7V while the load
is on. However once the load pulse ends, the battery volt-
DANGEROUS AND LETHAL POTENTIALS ARE PRESENT IN AC
LINE-CONNECTED CIRCUITS! BEFORE PROCEEDING ANY
FURTHER, THE READER IS WARNED THAT CAUTION MUST BE
USED IN THE CONSTRUCTION, TESTING AND USE OF AC
LINE-CONNECTED CIRCUITS. EXTREME CAUTION MUST BE
USED IN WORKING WITH AND MAKING CONNECTIONS TO
THESE CIRCUITS. ALL TESTING PERFORMED ON AC
LINE-CONNECTED CIRCUITS MUST BE DONE WITH AN
ISOLATION TRANSFORMER CONNECTED BETWEEN THE AC LINE
AND THE CIRCUIT. USERS AND CONSTRUCTORS OF AC
LINE-CONNECTED CIRCUITS MUST OBSERVE THIS PRECAUTION
WHEN CONNECTING TEST EQUIPMENT TO THE CIRCUIT TO
AVOID ELECTRIC SHOCK.
Figure 5. 4.2V AC Line Charging, UL Leakage Okay
4071fc
12
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
