Data Sheet

In constant current mode, the stability is also affected by the impedance at the ISET pin . With no additional
capacitance on the ISET pin, the loop is stable with current set resistors values as high as 50KΩ. However,
additional capacitance on ISET pin reduces the maximum allowed current set resistor. The pole frequency at
ISET pin should be kept above 200KHz. Therefore, if ISET pin is loaded with a capacitance C, the following
equation should be used to calculate the maximum resistance value for R
ISET
:
R
ISET
< 1／(6.28×2×10
5
×C)
In order to measure average charge current or isolate capacitive load from ISET pin, a simple RC filter can be
used on ISET pin as shown in Figure 7.
CN3083
ISET
RISET
10K
C
filter
Figure 7 Isolating Capacitive Load on ISET Pin
Board Layout Considerations
1. R
ISET
at ISET pin should be as close to CN3083 as possible, also the parasitic capacitance at ISET pin
should be kept as small as possible.
2. The capacitance at VIN pin and BAT pin should be as close to CN3083 as possible.
3. During charging, CN3083’s temperature may be high, the NTC thermistor should be placed far enough to
CN3083 so that the thermistor can reflect the battery’s temperature correctly.
4. It is very important to use a good thermal PC board layout to maximize charging current. The thermal path
for the heat generated by the IC is from the die to the copper lead frame through the package lead(especially
the ground lead) to the PC board copper, the PC board copper is the heat sink. The footprint copper pads
should be as wide as possible and expand out to larger copper areas to spread and dissipate the heat to the
surrounding ambient. Feedthrough vias to inner or backside copper layers are also useful in improving the
overall thermal performance of the charger. Other heat sources on the board, not related to the charger,
must also be considered when designing a PC board layout because they will affect overall temperature rise
and the maximum charge current.
The ability to deliver maximum charge current under all conditions require that the exposed metal pad on
the back side of the CN3083 package be soldered to the PC board ground. Failure to make the thermal
contact between the exposed pad on the backside of the package and the copper board will result in larger
thermal resistance.
REV 1.1 10