LTC4071
block DiagraM
V
IN
LTC4071
ADJ
PULSED
DUTY CYCLE = 0.003%
30µs – 200µs
0.9sec – 7sec
NTCBIAS
R
NOM
10k
CLK
V
CC
R
IN
SYSTEM
LOAD
3-STATE
DETECT
OSC
BODY
DIODE
MP1
BAT
NTC
ADC
T 10k
LBSEL
LBSEL MUST BE TIED TO V
CC
OR GND
HBO
+
–
1.2V
1.2V
operaTion
The LTC4071 provides a simple, reliable, and high per-
formance battery protection and charging solution by
preventing the battery voltage from exceeding a pro-
grammed level. Its shunt architecture requires just one
resistor from the input supply to charge and protect the
battery in a wide range of battery applications. When the
input supply is removed and the battery voltage is below
the high battery output threshold, the LTC4071 consumes
just 550nA from the battery. If the battery voltage falls
below the programmable low battery disconnect level,
the battery disconnects from V
CC
, protecting the battery
from over-discharge either by the load connected to V
CC
or from the LTC4071 quiescent current.
When an input supply is present the battery charges
through the body diode of the internal disconnect PFET,
MP1, until the battery voltage rises above the low-
battery connect threshold. Select an input voltage large
enough for V
CC
to reach V
LBC_VCC
to ensure that MP1 turns
on. The user may detect the connected state by observing
periodic pulses at the NTCBIAS pin that only occur once
V
CC
has risen above V
LBC_VCC
, and cease once V
CC
falls
below V
LBD
. Depending on the capacity of the battery and
the input decoupling capacitor, the V
CC
voltage generally
falls to V
BAT
when MP1 turns on; rather than V
BAT
rising
to V
CC
. The internal PFET then reconnects the battery to
V
CC
and the charge rate is determined by the input voltage,
the battery voltage, and the input resistor:
I
CHG
=
As the battery voltage approaches the float voltage, the
LTC4071 shunts current away from the battery thereby
reducing the charge current. The LTC4071 can shunt up to
50mA. The shunt current limits the maximum charge current.
4071fc
–
+
–
+
EA
+
Li-Ion
BATTERY
MP2
GND
4071 BD
(
V
IN
−
V
BAT
)
R
IN
7
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
