MAX8900B データシートの表示（PDF） - Maxim Integrated

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MAX8900B

1.2A Switch-Mode Li+ Chargers with ±22V Input Rating and JEITA Battery Temperature Monitoring

Maxim Integrated 

MAX8900A/MAX8900B/MAX8900C

1.2A Switch-Mode Li+ Chargers with ±22V Input

Rating and JEITA Battery Temperature Monitoring

Table 1. 2.44mm x 2.67mm x

0.64mm, 0.4mm Pitch WLP Thermal

Characteristics

Continuous Power

Dissipation

BJA

BJC

Board Parameters

FOUR-LAYER PCB

(JESD51-9:2s2p)

1619mW

Derate 20.2mW/NC above

+70NC/W

49.4NC/W

9NC/W

• Still air

• 4-layer board

• 1.5oz copper on outer layers

• 1oz copper on inner layers

• 1.6mm thick board (62mil)

• 4in x 4in board

• Four center thermal vias

• FR-4

several thermal management techniques to prevent

excessive battery and die temperatures.

Thermistor Monitor (THM)

The MAX8900_ adjusts the charge current and termina-

tion voltage as described in the JEITA specification for

safe use of secondary Li+ batteries (A Guide to the Safe

Use of Secondary Lithium Ion Batteries in Notebook-type

Personal Computers, April 20, 2007). As shown in Figure

10, there are four temperature thresholds that change

the battery charger operation: T1, T2, T3, and T4. When

the thermistor input exceeds the extreme temperatures

(< T1 or > T4), the charger shuts off and all respective

charging timers are suspended. While the thermistor

remains out of range, no charging occurs, and the timer

counters hold their state. When the thermistor input

comes back into range, the charge timers continue to

count. The middle thresholds (T2 and T3) do not shut

the charger off, but adjust the current/voltage targets

to maximize charging while reducing battery stress.

Between T3 and T4, the voltage target is reduced (see

VBATREG in the Electrical Characteristics table); how-

ever, the charge timers continue to count. Between T1

and T2, the charging current target is reduced to 50%

of its normal operating value; and similarly the charge

timers continue to count.

If the thermistor functionality is not required, connect a

1MI resistor from THM to AVL and another 1MI resis-

tor from THM to GND. This biases the THM node to be

½ of the AVL voltage telling the MAX8900_ that the bat-

tery temperature is between the T2 and T3 temperature

range. Furthermore, the high 2MI impedance presents

a minimal load to AVL.

Table 2 shows that the MAX8900_ is compatible with

several standard thermistor values. When using a 10kI

thermistor with a beta of 3380K, the configuration of

Figure 11A provides for temperature trip thresholds that

are very close to the nominal T1, T2, T3, and T4 (see the

Electrical Characteristics table). When using alternate

resistance and/or beta thermistors, the circuit of Figure

11A may result in temperature trip thresholds that are

different from the nominal values. In this case, the circuit

of Figure 11B allows for compensating the thermistor to

shift the temperature trip thresholds back to the nomi-

nal value. In general, smaller values of RTP shift all the

temperature trip thresholds down; however, the lower

temperature thresholds are affected more then the higher

temperature thresholds. Furthermore, larger values of RTS

shift all the temperature trip thresholds up; however, the

higher temperature thresholds are affected more than the

lower temperature thresholds. For assistance with therm-

istor calculations, use the spreadsheet at the following

link: www.maximintegrated.com/tools/other/software/

MAX8900-THERMISTOR.XLS

The general relation of thermistor resistance to tempera-

ture is defined by the following equation:

R

THRM

=

R 25

β

xe





1 -1

T+273NC 298NC





where:

RTHRM = The resistance in I of the thermistor at tem-

perature T in Celsius.

R25 = The resistance in I of the thermistor at TA =

+25NC.

ß = The material constant of the thermistor, which

typically ranges from 3000K to 5000K.

T = The temperature of the thermistor in NC.

24  

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