LTC4011 Linear Technology, LTC4011 Datasheet - Page 19

• Manufacturer Part Number: LTC4011
• Description: High Efficiency Standalone Nickel Battery Charger
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
Waveforms
Sample waveforms for a standalone application during a
typical charge cycle are shown in Figure 10. Note that
these waveforms are not to scale and do not represent the
complete range of possible activity. The figure is simply
intended to allow better conceptual understanding and to
highlight the relative behavior of certain signals generated
by the LTC4011 during a typical charge cycle.
Initially, the LTC4011 is in low power shutdown as the
system operates from a heavily discharged battery. A DC
adapter is then connected such that V
and is 500mV above BAT. The READY output is asserted
when the LTC4011 completes charge qualification.
When the LTC4011 determines charging should begin, it
starts a precharge cycle because V
As long as the temperature remains within prescribed
limits, the LTC4011 charges (TGATE switching), applying
limited current to the battery with the PWM in order to
bring the average cell voltage to 900mV.
4
U
4.5V TO 34V
ADAPTER
STATUS
U
FROM
MCU
TO
PAUSE
FROM
MCU
CELL
W
CC
V
is less than 900mV.
+
20k
rises above 4.25V
Figure 9. LTC4011 with MCU Interface
49.9k
U
Q1
0.1µF
INFET
FAULT
CHRG
TOC
READY
DCIN
TIMER
GND
CHEM
V
INTV
RT
LTC4011
DD
SENSE
TGATE
BGATE
V
PGND
V
V
TEMP
CELL
BAT
CDIV
When the precharge state timer expires, the LTC4011 be-
gins fast charge if V
charge timer and internal termination control are sus-
pended if pause is asserted (V
outputs continue to indicate charging is in progress. The
fast charge state continues until the selected voltage or
temperature termination criteria are met. Figure 10 sug-
gests termination based on ∆T/∆t, which for NiMH would
be an increase of 1°C per minute.
Because NiMH charging terminated due to ∆T/∆t and the
fast charge cycle had lasted more than t
the LTC4011 begins a top-off charge with a current of
I
minutes with the CHRG and TOC outputs continuously
asserted.
Finally, the LTC4011 enters the automatic recharge state
where the CHRG and TOC outputs are deasserted. The
PWM is disabled but V
V
resume if V
V
PROG
CC
CELL
10k
/10. Top-off is an internally timed charge of t
. The charge timer will be reset and fast charging will
Q2
Q3
10.7k
R2
33nF
CELL
68nF
drops below 1.325V. The LTC4011 enters
CELL
30.9k
10µF
CDIV
is greater than 900mV. The PWM,
remains asserted to monitor
CELL
10µH
0.1Ω
4011 F09
< 200mV), but all status
TO
SYSTEM
LOAD
NiCd PACK
WITH 10k NTC
(1AHr)
MAX
LTC4011
/12 minutes,
19
MAX
4011p
/3