LTC4010 Datasheet, PDF (14/20 Pages) Linear Integrated Systems – High Efficiency Standalone Nickel Battery Charger

LTC4010
APPLICATIO S I FOR ATIO
the application will depend on the amount of PCB copper
to which the package is soldered. Feedthrough vias di-
rectly below the package that connect to inner copper
layers are helpful in lowering thermal resistance. The fol-
lowing formula may be used to estimate the maximum
average power dissipation P_D (in watts) of the LTC4010
under normal operating conditions.
( ) ^P_D ^{= V}_CC ^{7.3mA + I}_DD ^{+ 615k(Q}_TGATE ^{+ Q}_BGATE⁾
–
3.85I_DD
+
60n^{⎛⎝⎜}
V_CC –
R_LED
V_LED
+ 30
⎞²
⎠⎟
where:
I_DD = Average external INTV_DD load current, if any
Q_TGATE = Gate charge of external P-channel MOSFET
in coulombs
Q_BGATE = Gate charge of external N-channel MOSFET
(if used) in coulombs
V_LED = Maximum external LED forward voltage
R_LED = External LED current-limiting resistor used in
the application
n = Number of LEDs driven by the LTC4010
Sample Applications
Figures 6 through 8 detail sample charger applications
of various complexities. Combined with the Typical
Application on the first page of this data sheet, these
figures demonstrate some of the proper configurations
of the LTC4010. MOSFET body diodes are shown in these
figures strictly for reference only.
Figure 6 shows a minimum application, which might be
encountered in low cost NiCd fast charge applications. The
LTC4010 uses –∆V to terminate the fast charge state, as
no external temperature information is available.
Nonsynchronous PWM switching is employed to reduce
external component cost. A single LED indicates charging
status.
A full-featured 2A LTC4010 application is shown in Fig-
ure 7. The inherent voltage ratings of the V_CELL, V_CDIV,
SENSE and BAT pins allow charging of from one to sixteen
series nickel cells in this application, governed only by the
V_CC overhead limits previously discussed. The application
includes all average cell voltage and battery temperature
sensing circuitry required for the LTC4010 to utilize its full
range of charge qualification, safety monitoring and fast
charge termination features. The V_TEMP thermister net-
work allows the LTC4010 to accurately terminate fast
charge under a variety of applied charge rates. Use of a
synchronous PWM topology improves efficiency and re-
duces excess heat generation. A green LED indicates valid
DC input voltage and installed battery, while a red LED
indicates charging. Fault conditions are indicated by a
yellow LED. The grounded CHEM pin selects the NiMH
charge termination parameter set.
FROM
ADAPTER
5.5V TO 34V
3k
10µF
LTC4010
V_CC
R
FAULT TGATE
CHRG
READY
BGATE
49.9k
TIMER PGND
SENSE
GND
BAT
0.1µF
10k
V_CDIV
CHEM V_CELL
INTV_DD V_TEMP
56k
10µH
0.1Ω
10µF
33nF
TO
SYSTEM
LOAD
NiCd
PACK
4010 F06
Figure 6. Minimum LTC4010 Application
4010p
14