UB2016

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

9 of 13

www.unisonic.com.tw

QW-R502-869.a

APPLICATION INFORMATION(Cont.)

Thermal Considerations

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. Feed-through 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 following table lists thermal resistance for several

different board sizes and copper areas. All measurements were taken in still air on 3/32" FR-4 board with the device

mounted on topside.

Table 1 Measured Thermal Resistance on 2-Layer Board (Note 1)

COPPER AREA

BOARD AREA

JUNCTION-TO-AMBIENT

TOPSIDE

BACKSIDE

2500mm

2

2500mm

2

2500mm

2

125°C/W

1000mm

2

2500mm

2

2500mm

2

125°C/W

225mm

2

2500mm

2

2500mm

2

130°C/W

100mm

2

2500mm

2

2500mm

2

135°C/W

50mm

2

2500mm

2

2500mm

2

150°C/W

Note:

1. Each layer uses one ounce copper

Table 2 Measured Thermal Resistance on 4-Layer Board (Note 1)

COPPER AREA (EACH SIDE)

BOARD AREA

2500mm

2500mm

2

80°C/W

Notes:

1.

Top and bottom layers use two ounce copper, inner layer use one ounce copper

2.

10,000mm

Increasing Thermal Regulation 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. While this application

delivers more energy to the battery and reduces charge time in thermal mode, it may actually lengthen charge time

result in dropout as RCC becomes large. This technique works best when RCC values are minimized to keep

component size small and avoid dropout. Remember to choose a resistor with adequate power handling capability.

UTC

UB2016

PROG

BAT

2kΩ

+

Li-Ion

BATTERY

Rcc

1µF

GND

5V

Fig. 2 A Circuit to Maximize Thermal Mode Charge Current