LTC4008EGN Linear Technology, LTC4008EGN Datasheet - Page 17

• Manufacturer Part Number: LTC4008EGN
• Description: IC BATT CHARGER CTRLR 4A 20SSOP
• Manufacturer: Linear Technology

Specifications of LTC4008EGN

• Function: Charge Management
• Battery Type: Multi-Chemistry
• Voltage - Supply: 6 V ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-SSOP (0.154", 3.91mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS INFORMATION
used, with closed-loop feedback ensuring that adapter load
current remains within limits. Amplifi er CL1 in Figure 7
senses the voltage across R
CLP and CLN pins. When this voltage exceeds 100mV,
the amplifi er will override programmed charging current
to limit adapter current to 100mV/R
formed by 5kΩ and 15nF is required to eliminate switch-
ing noise. If the current limit is not used, CLN should be
connected to CLP .
Note that the I
across R
threshold.
Setting Input Current Limit
To set the input current limit, you need to know the mini-
mum wall adapter current rating. Subtract 7% for the input
current limit tolerance and use that current to determine
the resistor value.
*R
R
I
LTC4008
LIM
CL
CL
=
= 100mV/I
= Adapter Min Current –
ADAPTER CURRENT LIMIT
(Adapter Min Current • 7%)
CL
CL1
is 93mV, before the adapter limit regulation
Figure 7. Adapter Current Limiting
100mV
–
+
CL
LIM
pin will be asserted when the voltage
100mV
16
15
4008 F07
CLP
CLN
CL
, connected between the
15nF
R
V
CL
IN
*
CL
5k
. A lowpass fi lter
+
C
IN
TO
SYSTEM
LOAD
Table 5. Common R
*Values shown above are rounded to nearest standard value.
As is often the case, the wall adapter will usually have at
least a +10% current limit margin and many times one
can simply set the adapter current limit value to the actual
adapter rating (see Table 5).
Designing the Thermistor Network
There are several networks that will yield the desired
function of voltage vs temperature needed for proper
operation of the thermistor. The simplest of these is the
voltage divider shown in Figure 8. Unfortunately, since
the HIGH/LOW comparator thresholds are fi xed internally,
there is only one thermistor type that can be used in this
network; the thermistor must have a HIGH/LOW resistance
ratio of 1:7. If this happy circumstance is true for you, then
simply set R9 = R
RATING (A)
ADAPTER
1.5
1.8
2.3
2.5
2.7
2
3
Figure 8. Voltage Divider Thermistor Network
LTC4008
R
CL
CL
(Ω) 1%
NTC
TH(LOW)
0.045
0.039
0.036
0.033
0.06
0.05
0.03
VALUE*
Resistor Values
8
R9
DISSIPATION (W)
R
CL
C7
0.135
0.162
0.206
0.225
0.241
0.18
0.27
POWER
4008 F08
LTC4008
R
TH
R
RATING (W)
CL
0.25
0.25
0.25
0.25
POWER
0.5
0.5
0.5
17
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