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Technical content

Features

 Precise Threshold: ±2%  Adjustable Hysteresis to Eliminate the Output Chatter  Active-low and Active-high CMOS Outputs  9.5µA Supply Current @VCC=3V  Power Supply Transient Immunity  Operating Temperature Range -40°C to +85°C  Available in SOT23-6  Lead-free, Rohs-compliant and Halogen-free Pin Assignment VCCLBO GND CN302 3 4

6 RTH

w w w . c o n s o n a n c e - e l e c . c o m 3 R e v 1 . 0 Pin Description Pin No. Symbol Description 1 FTH Falling Threshold Input. Generally FTH pin should be tied to an external resistor divider to sense the battery voltage.

2 GND Negative Terminal of Power Supply(Ground)

3 LBO

Active-High Low Battery Output. CMOS output. When the voltage at RTH pin rises above the internal reference voltage, LBO becomes low; When the voltage at FTH pin falls below the internal reference voltage, LBO becomes high. 4 VCC Positive Terminal of Power Supply. This pin is the power supply to internal circuit. Active-Low Low Battery Output. CMOS output. When the voltage at RTH pin rises above the internal reference voltage, becomes high; When the voltage at FTH pin falls below the internal reference voltage, becomes low. 6 RTH Rising Threshold Input. Generally RTH pin should be tied to an external resistor divider to sense the battery voltage. ABSOLUTE MAXIMUM RATINGS Terminal Voltage (With respect to GND) Input/Output Current Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

Electrical Characteristics

(VCC=3V , TA= －40℃ to 85 ℃, Typical values are at TA=25℃, unless otherwise noted.) Parameters Symbol Test Conditions M i n T y p M a x U n i t Operating V oltage Range V C C 1 . 9 6 V Operating Current I VCC VCC＝1.8V 4.4 8 . 8 1 4 uA VCC＝3.0V 5 9 . 5 1 4 VCC＝5.0V 5 1 0 1 5 RTH Bias Current I RTH －100 0 100 nA FTH Bias Current I FTH －100 0 100 nA

w w w . c o n s o n a n c e - e l e c . c o m 4 R e v 1 . 0 (Continued from last page) Parameters Symbol Test Conditions M i n T y p M a x U n i t RTH to LBO Delay t PD1 RTH＝1.167V to 1.255V 12 us FTH to LBO Delay t PD2 FTH＝1.255V to 1.167V 13 us LBO or Low V oltage VOL VCC＝2V , ISINK＝1.5mA 0.3 V VCC＝3V , I SINK＝3.2mA 0 . 3 VCC＝5V , I SINK=6mA 0 . 3 LBO or High V oltage VOH VCC＝2V , ISOURCE=1.5mA VCC－0.4 V VCC＝3V , ISOURCE＝3mA VCC－0.4 VCC＝5V , VLBI＝1.5V ISOURCE＝5mA VCC－0.4 Detailed Description CN302 is a low power battery monitor IC with hysteresis control, the device consists of comparator, bandgap reference and hysteresis control circuit etc. If the voltage at FTH pin falls below the falling threshold VFTH, will become low and LBO will become high after a short delay(13us typical); If the voltage at RTH pin goes higher than the rising threshold VRTH, will become high and LBO will become low after a delay of 12us typical. The difference between rising threshold and falling threshold is also called hysteresis, which can provide noise immunity and remove the possibility of output chatter due to battery terminal voltage recovery after the load removal. The CN302 allows for wide hysteresis by adjusting the rising and falling threshold independently. CN302 is specially designed for monitoring single or multi lithium-ion (Li+) cells, multi-cell alkaline, NiCd, NiMH and multi-cell lead acid batteries. The operation of the device can be best understood by referring to figure 3. FTH VFTH VRTH LBO RTH LBO Figure 3 Timing waveform

w w w . c o n s o n a n c e - e l e c . c o m 5 R e v 1 . 0 Applications Information R1, R2 and R3 Selection As shown in Figure 1 and Figure 2, RTH and FTH pins sense the battery voltage via the resistor divider formed by R1, R2 and R3. Choosing the proper R1, R2 and R3 values is a balance between accuracy and power consumption. The leakage currents into RTH and FTH pins travel through the resistor divider and introduce an error, If extremely high resistor values are used, the leakage current introduces a significant error; While with extremely low resistor values, the error becomes negligible, but the resistor divider draws more power from the battery than necessary and shortens battery life. Generally speaking, it is reasonable to choose the total value of R1, R2 and R3 so that the current they draw is between 5uA to 10uA. The rising threshold is calculated by the following equation: The falling threshold is calculated by the following equation: Where, Vref is the internal reference voltage, the typical value is 1.211V with 2% accuracy. So, the hysteresis is: It is interesting to note that: and Adding External Capacitance to Enhance Noise Immunity If monitoring voltages in a noisy environment, add a bypass capacitor of 0.1μF from battery terminal to GND as close as possible to the device. For systems with large transients, additional capacitance may be required. A small capacitor (<1nF) from RTH and FTH pin to GND may provide additional noise immunity. Negative-Going LBI Transients In addition to issuing a low output at pin and a high output at LBO pin during power-up, power-down, and brownout conditions of the monitored voltage, the CN302 is relatively immune to short-duration negative-going FTH transients (glitches). As the magnitude of the transient increases (goes farther below the falling threshold), the maximum allowable pulse width decreases. Typically, a FTH transient that goes 20mV below the falling threshold and lasts 5µs or less will not cause a low output and a high LBO output. A bypass capacitor from FTH pin to GND provides additional transient immunity. CN302 discontinues the battery discharge CN302 can monitor the battery voltage and discontinue the discharge by cutting off external N channel or P channel MOSFET as shown from Figure 4 to Figure 7.

w w w . c o n s o n a n c e - e l e c . c o m 8 R e v 1 . 0 Figure 9 Power CN302 from a Resistor Divider

w w w . c o n s o n a n c e - e l e c . c o m 9 R e v 1 . 0

Package Information

Consonance does not assume any responsibility for use of any circuitry described. Consonance reserves the right to change the circuitry and specifications without notice at any time.