ME4057

V01

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Page 9 of 18

output connected to GND.

charger’s status

Red led

Green led

Charging

light

dark

Battery in full state

dark

light

Under-

voltage, battery’s temperature is to high or too low, or not

connect to battery(use TEMP)

dark

dark

BAT pin is connected to 10uF capacitor ， No battery mode

(TEMP=GND)

Green LED bright, Red LED flicker F=1-4 S

Thermal limiting

An internal thermal feedback loop reduces the programmed charge current if the die temperature attempts to

rise above a preset value of approximately 140℃ . The feature protects the ME4057 from excessive temperature and

allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the

ME4057. The charge current can be set according to typical (not worst-case) ambient temperature with the

assurance that the charger will automatically reduce the current in worst-case conditions.

To prevent the damage caused by the very high or very low temperature done to the battery pack, the ME4057

continuously senses battery pack temperature by measuring the voltage at TEMP pin determined by the voltage

divider circuit and the battery’s internal NTC thermistor as shown in Figure 1.

The ME4057 compares the voltage at TEMP pin (VTEMP) against its internal VLOW and VHIGH thresholds to

determine if charging is allowed. In ME4057, VLOW is fixed at (45%×Vcc), while VHIGH is fixed at (80%×Vcc). If

VTEMP<VLOW or VTEMP>VHIGH , it indicates that the battery temperature is too high or too low and the charge cycle is

suspended. When VTEMP is between VLOW and VHIGH, charge cycle resumes. The battery temperature sense

function can be disabled by connecting TEMP pin to GND.

Selecting R1 and R2

The values of R1 and R2 in the application circuit can be determined according to the assumed temperature

monitor range and thermistor’s values. The Follows is an example: Assume temperature monitor range is T

L～TH，

（ T

L＜TH)；the thermistor in battery has negative temperature coefficient（NTC, RTL is thermistor’s resistance at TL，

RTH is the resistance at TH，so RTL＞RTH，then at temperature TL, the voltage at TEMP pin is:

At temperature TH, the voltage at TEMP pin is:

We know VTEMPL＝VHIGH＝K2×Vcc (K2=0.8)；VTEMPH＝VLOW＝K1×Vcc (K1=0.45) Then we can have：

For example, NCP03YS110 , operating Temperature is -40℃ to 125℃. If using environment temperature is -25℃ to

125℃, then RTL is the value of the resistance of NCP03YS110 at -25℃, about 66.148Ω; RTH=is the value of the

resistance of NCP03YS110 at 125℃, about

1.077Ω.