MAX2003 Maxim Integrated Products, MAX2003 Datasheet - Page 14

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

From solving these simultaneous equations:
R
R
Using R
1.72V, and V
= 1.599kΩ and R
Select preferred resistor values for R
R
can be verified as follows:
7) Select Maximum Cell Voltage (MCV) and
Temperature Cutoff (TCO). The MCV and TCO can be
selected with a resistor-divider combination (Figure 9).
In our example, TCO has been set to +10°C, which cor-
responds to a voltage of 1.72V at the TS pin. The MCV
for most fast-charge batteries can be set to about 1.9V.
To minimize the current load on V
range of 20kΩ to 200kΩ. In this example, choose R1 =
60.4kΩ, then calculate R3 and R2 as follows:
Select preferred resistor values for R2 (3.48kΩ) and R3
(33.2kΩ). The actual voltages on MCV and TCO can be
verified as follows :
NiCd/NiMH Battery
Fast-Charge Controllers
14
where X = _____________________________
T1
NTC10
T2
R2 = (V
V
R3 = (V
MCV
= [(R
(1.62kΩ). The actual voltages on MCV and TCO
______________________________________________________________________________________
V
TCO
R
V
V
)].
NTC50
TS10
TS50
T2
MCV
= V
T2
TCO
= [(X) (R
[(R
= V
) (R
[(R
CC
TS10
x R1) / (V
NTC10
NTC50
= 4.16kΩ, R
CC
x R1) / (V
(R2 + R3) / (R1 + R2 + R3) = 1.89V.
NTC10
1.72V
2.01V
T2
= 2.00V, it can be calculated that R
1.62k II 17.96k
1.62k II 4.16k
(R3) / (R1 + R2 + R3) = 1.71V
R
R
= 2.303kΩ.
V
V
NTC10
) (V
T2
T2
CC
CC
)(V
) (V
and
5 1.62k II 17.96k
5 1.62k II 4.16k
CC
and
II R
II R
TS10
TS50
R
R
CC
CC
) - (R
- V
T2
T2
NTC10
NTC50
NTC10
)(V
) (V
- V
MCV
II R
II R
- V
NTC50
MCV
CC
CC
TS10
NTC10
NTC50
) - R3 = 3.51kΩ (1%)
CC
- V
= 17.96kΩ, V
- V
) = 33.5kΩ (1%)
, choose R1 in the
)] / (1 - X)
)] / [V
TS50
R
R
TS10
T1
T1
T1
2.21k
2.21k
)]
(2.21kΩ) and
)]
TS10
TS50
(R
T2
T1
+
=
8) Select Trickle Resistor (MAX2003 only). The trick-
le resistor (R
rate of C/16 to C/40. The resistor value is given by:
where I
supply voltage, and V
the cell voltage after fast-charge.
In our example, the 1700mAh NiMH battery needs a
trickle current of C/40; i.e., 42mA (1700mAh/40h).
Therefore, the minimum voltage (from the formula
above) is as follows:
The maximum power dissipated in the resistor can be
calculated by:
where V
DC supply voltage, and R
Since a shorted battery could have 0V, this must be the
minimum cell voltage possible. Therefore the power
dissipated in the trickle resistor would be:
A 2W, 150Ω resistor should be sufficient for the trickle-
charge resistor. For the MAX2003A, refer to Trickle-
Charge section.
9) Select Inductor. The inductor value can be calcu-
lated using the formula:
where V
is the minimum inductor value, i is the change in induc-
tor current, and t is the minimum on-time of the switch.
Figure 10. Inductor-Current Waveform in Continuous-
Conduction Mode
I
MAX
I
R
MIN
TR
TR
BAT(MIN)
L
= 1.9A
= 1.5A
I
is the maximum voltage across the inductor, L
LOAD
Power = (13 - 0)
is the required trickle current, V
= [13.0V - (6 x 1.2V)] / 42mA ≈ 150Ω
Power = (V
R
TR
TR
) is selected to allow a trickle-charge
= (V
is the minimum cell voltage, V
DC
V
DC
L
t
BAT
OFF
- V
= L
- V
TR
2
BAT
is the number of cells times
/ 150 = 1.2W
BAT(MIN)
t
ON
is the trickle resistor value.
i / t
) / I
i = I
MAX
TR
- I
)
MIN
2
/ R
TIME
TR
DC
is the DC
DC
is the