APPLICATIONS INFORMATION
Moreover, when thermal feedback reduces the charge
current, the voltage at the PROG pin is also reduced
proportionally as discussed in the Operation section.
It is important to remember that SGM4054 applications do
not need to be designed for worst-case thermal conditions
since the IC will automatically reduce power dissipation
when the junction temperature reaches approximately
120℃.
Table 2. Measured Thermal Resistance (4-Layer Board**)
COPPER AREA
(EACH SIDE)
BOARD
AREA
THERMAL RESISTANCE
JUNCTION-TO-AMBIENT
2
2
2500 mm
2500 mm
80℃/W
*Top and bottom layers use two ounce copper, inner layers
use one ounce copper.
2
**10,000mm total copper area
Thermal Considerations
Increasing Thermal Regulation Current
Because of the small size of the ThinSOT package, it is very
important to use a good thermal PC board layout to
maximize the available charge current. The thermal path
for the heat generated by the IC is from the die to the
copper lead frame, through the package leads, (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.
Reducing the voltage drop across the internal MOSFET can
significantly decrease the power dissipation in the IC. This
has the effect of increasing the current delivered to the
battery during thermal regulation. One method is by
dissipating some of the power through an external
component, such as a resistor or diode.
Example: An SGM4054 operating from a 5V wall adapter is
programmed to supply 800mA full-scale current to a
discharged Li-Ion battery with
a voltage of 3.75V.
Assuming θJA is 125°C/W, the approximate charge current
at an ambient temperature of 25°C is:
120C° − 25C°
(5V − 3.75V) •125C°/W
IBAT
=
= 608mA
The following table lists thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32ʺ FR-4 board with the device
mounted on topside.
By dropping voltage across a resistor in series with a 5V
wall adapter (shown in Figure 3), the on-chip power
dissipation can be decreased, thus increasing the thermally
regulated charge current：
Table 1. Measured Thermal Resistance (2-Layer Board*)
120C° − 25C°
THERMAL
RESISTANCE
JUNCTION-
TO-AMBIENT
125℃/W
COPPER AREA
TOPSIDE BACKSIDE
I
BAT
=
BOARD
AREA
(VS
− IBAT
RCC −VBAT) •
θJA
2
2
2
2
2
2
2
2500mm
2500mm
2500 mm
2500 mm
2500 mm
2500 mm
2500 mm
2
2
2
2
2
1000 mm
2500 mm
2500 mm
2500 mm
2500 mm
125℃/W
130℃/W
135℃/W
150℃/W
2
2
225 mm
100 mm
50 mm
2
*Each layer uses one ounce copper
10
SGM4054
TOREX [ Torex Semiconductor ]
