HM5081 datasheet(6/9 Pages) HMSEMI

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APPLICATION INFORMATION

HM5081

is a wide range VIN(4V-20V), 4.5A 1cell asynchronous boost Li-Ion battery charger integrates

500KHz switching frequency and full protection functions. The charge current can be programmed up

to Max 4.5A by using the external resistor for different portable applications and indicates the charger

current information simultaneous. In constant current mode, the charge current is set by the external

sense resistor RSNS and an internal 50mV reference;

IBAT=VRS/RSNS=50mV/RSNS

When the battery voltage approaches the programmed float voltage, the charge current will start to

decrease. When the current drops to 10% of the full-scale charge current, an internal comparator turns

off charging is terminated

Input Source Qualification

After REGN amplifier powers up, the HM5081 checks the current capability of the input source. The

input source has to meet the VREG>1V to enable the chip

Battery Temperature Detection

The HM5081 continuously monitors temperature by measuring the voltage between the NTC and GND

pins. A negative or a positive temperature coefficient thermistor (NTC, PTC) and an external voltage

divider typically develop this voltage. The HM5081 compares this voltage against its internal VNTC-H

and VNTC-L thresholds to determine if charging is allowed. The temperature sensing circuit is immune

to any fluctuation in LV5, since both the external voltage divider and the internal thresholds (VNTC-H

and VNTC-L) are referenced to LV5.

The resistor values of R1 and R2 are calculated by the following equations:

For NTC Thermistors:

K1 (VNTC-H) =30%,

K2 (VNTC-L) =70%.

Automatic Recharge

Once the charge cycle is terminated, the HM5081 continuously monitors the voltage on the BAT pin

using a comparator with a 1.8ms filter time (tRECHARGE). A charge cycle restarts when the battery

voltage falls below 4.05V (which corresponds to approximately 80% to 90% battery capacity). This

ensures that the battery is kept at or near a fully charged condition and eliminates the need for periodic

charge cycle initiations.

Where RTL is the low temperature resistance and RTH is the high temperature resistance of thermistor,

as specified by the thermistor manufacturer. R1 or R2 can be omitted if only one temperature (low or

high) setting is required. Applying a voltage between the VNTC-H and VNTC-L thresholds to pin NTC

disables the temperature-sensing feature.

4.5A Synchronous Buck Li-ion Charger

HM5081 Datasheet(PDF) 6 Page - Shenzhen Huazhimei Semiconductor Co., Ltd