Datasheet

LTC4071
12
4071fc
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.
Figure 5. 4.2V AC Line Charging, UL Leakage Okay
4071 F05
LTC4071
AC 110V
ADJNTC
BAT
GND
Li-Ion
BATTERY
NTCBIASFLOAT
V
CC
R1 = 249k R2 = 249k
LBSEL
+
SYSTEM
LOAD
MB4S
– +
DANGER! HIGH VOLTAGE
R3 = 249k R4 = 249k
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.
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
600mV
= 166.6µF
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,
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 P/N CAPACITY RESISTANCE V
MIN
CYMBET CBC012 12µAh 5k to 10k 3.0V
CYMBET CBC050 50µAh 1500Ω to 3k 3.0V
GS NanoTech N/A 500µAh 40Ω 3.0V
APS-Autec LIR2025 20mAh 0.75Ω 3.0V
APS-Autec LIR1025 6mAh 30Ω 2.75V
IPS MEC225-1P 0.13mAh 210Ω to 260Ω 2.1V
IPS MEC220-4P 0.4mAh 100Ω to 120Ω 2.1V
IPS MEC201-10P 1.0mAh 34Ω to 45Ω 2.1V
IPS MEC202-25P 2.5mAh 15Ω to 20Ω 2.1V
GM Battery GMB031009 8mAh 10Ω to 20Ω 2.75V
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-
LTC4071
BAT
NTCBIAS
NTC
LBSEL
ADJ
R
IN
V
IN
GND
Li-Ion
V
CC
+
C
BYPASS
4071 F04
FLOAT
10k
NTHS0402N02N1002F
T
PULSED
I
LOAD
SYSTEM LOAD