MAX2003 Maxim Integrated Products, MAX2003 Datasheet - Page 18

• Manufacturer Part Number: MAX2003
• Description: Nicd/nimh Battery Fast-charge Controllers
• Manufacturer: Maxim Integrated Products

current value must be sufficiently guardbanded to
ensure the limiting factor is the SNS resistor, and not
the transistor. In our example, the maximum current
supplied by the Darlington will be guardbanded to
1.8A. Since the beta of the Darlington is typically 1000,
the base current needed will be:
The emitter of the TIP115 will see 14V, so the base will
see about 12.6V. When the MOD pin is high, the
2N2222 transistor is on and the base resistor will be:
This 1.8A current will never be reached because MOD
will be off when the SNS voltage reaches 0.25V (0.9A).
NiCd/NiMH Battery
Fast-Charge Controllers
Table 7. Operation Summary
18
Battery Absent
Initiate Discharge
Initiate Fast-Charge
Charge Pending
Discharge
Fast-Charge
Charge Complete
Top-Off Charge
Constant Trickle-
Charge (MAX2003)
Pulsed Trickle-
Charge (MAX2003A)
Charge Status
______________________________________________________________________________________
I
R
B
B
= I
= V
C
B
/ BETA = 1.8A / 1000 = 1.8mA
/ I
B
= 12.6V / 1.8mA ≈ 6.8kΩ
(V
Rising edge on DCMD
a) Power applied and voltage at
CCMD = DCMD
b ) DCMD = Low, CCMD = Rising
Edge (power already present)
c ) DCMD = High, CCMD = Falling
Edge (power already present)
Fast-charge initiated and tempera-
ture or voltage outside the set limits.
Discharge initiated with temperature
and voltage within set limits.
Fast-charge initiated with tempera-
ture and voltage within set limits.
Exceed one of the five termination
conditions.
Charge complete and top-off
enabled without exceeding temper-
ature and voltage limits.
Trickle current provided by external
resistor after fast-charge/top-off.
Pulse current provided by pulsing
MOD pin after fast-charge/top-off.
BAT
- V
SNS
Conditions
) ≥ V
MCV
If V
If V
MAX2003A: Activate for 0.5sec in
every 4sec period.
MAX2003: Active for 4sec in
every 34sec period.
Pulsed according to charge rate
(Table 4).
SNS
SNS
The circuit in Figure 12 is set up to charge a Duracell
DR35 battery pack (nine cells, 2.6Ah) using a 19V, 2.6A
current-limited power supply provided by Advanced
Power Solutions. Since many power supplies have
built-in current limiting, very few external components
are required for this charging method.
The SNS pin in this circuit is tied directly to V
signals the MOD pin to stay high until a termination
condition is met. When MOD is high, the NPN transistor
is turned on, hence pulling the gate of the MOSFET low.
This turns the MOSFET on and supplies current to the
battery at the current limit of the source (2.6A). The 12V
zener diode is placed between the source and gate of
the FET to ensure the FET’s maximum source-drain
voltage is not exceeded.
When a termination condition is reached, the MOD pin
goes low to turn off the FET and terminate the fast-
charge current.
> 0.044V
> 0.050V
MOD Status
Low
Low
Low
Low
Low
Low
Low
CC
CC
, MOD = High
, MOD = Low
Current-Limited Supply
Status
High
Low
Low
Low
Low
Low
Low
Low
Low
Low
DIS
Continuous
LED On
(Low)
0.125
1.375
0.125
0.125
0.125
0.125
(sec)
—
—
—
CHG LED Status
Continuous
Continuous
Continuous
LED Off
SS
(High)
(sec)
1.375
0.125
0.125
0.125
0.125
0.125
. This
—