Linear Technology LTC4070EDDB Demo Board, Simple Low-Iq Battery Charger/Protector with NTC Thermistor Input DC1584A DC1584A 데이터 시트

제품 코드

DC1584A

LTC4070

4070fc

Typical applicaTions

The LTC4070 can be used to charge a battery to a 4.2V

float voltage from an AC line with a bridge rectifier as

shown in the simple schematic in Figure 5. In this example,

the four input 249k resistors are sized for acceptable UL

leakage in the event that one of the resistors short. Here,

the LTC4070 will fully charge the battery from the AC line

while meeting the UL specification with only 104µA of

available charge current.
A photovoltaic (PV) application for the LTC4070 is illus-

trated in Figure 6. In this application, transistor Q1 has

been added to further reduce the already low quiescent

current of the LTC4070 to achieve extremely low battery

discharge when the PV cells are not charging the battery.

In long battery life applications, Q1 isolates the battery

from the LTC4070 when Q1’s base voltage falls. Under

normal operation, the PV cells provide current through the

and V

diodes of Q1. While the battery is charging,

the majority of PV current flows to the battery. When V

reaches the programmed float voltage, in this case 4.1V

with ADJ floating, then the LTC4070 shunts base-collector

junction current from Q1, effectively reducing the battery

charging current to zero and saturating Q1. In the event

that the thermistor temperature rises and the float voltage

drops, the LTC4070 shunts more current, and Q1 is forced

to operate in reverse active mode until the battery voltage

falls. Once equilibrium is achieved, the difference between

BAT

and V

should be less than a few mV, depending on

the magnitude of the shunt current.
Add a series input resistor, R

, to limit the current from

high current solar cells. Solar cells are limited in current

normally, so for small cells no resistor is needed. With

high current PV cells, select R

taking into account the

PV cell’s open-circuit voltage and short-circuit current,

the temperature coefficient of the V

and V

diodes and

the maximum collector current and operating junction

temperature of Q1. Using an isolating transistor reduces

discharge current to a few nanoamps, and may be extended

to other applications as well.
The PV application schematic in Figure 6 also illustrates

using the LTC4070 with a 10k, 5% curve 2 type NTC

thermistor, NTHS0402N02N1002F. Here R

NOM

is 10k,

and the rising temperature trip points are 40°C, 50°C,

60°C and 70°C.

Figure 6. Photovoltaic Charger with Extremely

Low Leakage When Not Charging

Figure 5. 4.2V AC Line Charging, UL Leakage Okay

FLOAT

IF NOT

NEEDED

4070 F05

LTC4070

AC 110

DANGER! HIGH VOLTAGE!

GND

NTCBIAS

MB4S

NTC

Li-Ion

BATTERY

249k

ADJ

249k

–

DANGEROUS AND LETHAL POTENTIALS ARE PRESENT IN AC

LINE-CONNECTED CIRCUITS! BEFORE PROCEEDING ANY FURTHER,

THE READER IS WARNED THAT CAUTION MUST BE USED IN THE

CONSTRUCTION, TESTING AND USE OF AC LINE-CONNECTED

CIRCUITS. EXTREME CAUTION MUST BE USED IN WORKING WITH

AND MAKING CONNECTIONS TO THESE CIRCUITS. ALL TESTING

PERFORMED ON AN AC LINE-CONNECTED CIRCUIT MUST BE DONE

WITH AN ISOLATION TRANSFORMER CONNECTED BETWEEN THE

AC LINE AND THE CIRCUIT. USERS AND CONSTRUCTORS OF AC

LINE-CONNECTED CIRCUITS MUST OBSERVE THIS PRECAUTION

WHEN CONNECTING TEST EQUIPMENT TO THE CIRCUIT TO AVOID

ELECTRIC SHOCK.

4070 F06

LTC4070

ADJ

NTC

: NTHS0402N02N1002F 10k

GND

FLOAT

MP5650

NOM

10k

Li-Ion

NTCBIAS

NTC

BAT

OR 2N3904

0.1µF

+
–