LTC4070

13

4070f

4070 F07

LTC4070

ADJ

HBO

LBO

D1

LTST

C190CKT

OPTIONAL

D3

BAS416

D2

LTST

C190GKT

GND

FLOAT

T

10k

Li-Ion

NTCBIAS

NTC

1k

1k

205Ω

1W

+

TYPICAL APPLICATIONS

The LTC4070 status pins have sufficient drive strength to

use with an LED, for a visual indication of charging status.

Consider the application in Figure 7, where red LED D1 is

connected to the LBO pin and turns off when the battery

nected to the HBO pin turns on while the battery is charging.

to indicate that the battery is no longer charging. Optionally,

a low leakage diode D3 is placed between the cathode of

D2 and the battery. This diode stops D2 from discharging

the battery when the input supply is not present.

shunt current of 50mA that occurs at the maximum input

voltage of 15V and the minimum NTC qualified float voltage

Figure 7. Single Cell Charger with LED Status and

NTC Qualified Float Voltage

of 3.8V, assuming the voltage drop on diode D3 is 1.1V.

Figure 8 illustrates an application to replace three NiMH cells

with a single Li-Ion cell. This simple application replaces

the NiMH charging solution without the need for a charge

termination or cell balancing scheme. NiMH charging can

be done without termination, but that algorithm limits the

charge rate to C/10. The LTC4070 application allows the

Li-Ion battery to be charged faster without concern of

over-charging.

Figure 9, 12V Wall Adapter Charging with 205mA, il-

lustrates the use of an external PFET transistor to boost

the maximum shunt current. If the battery voltage is

3.6V the battery receives the full charge current of

about 205mA. If the battery temperature is below 40°C,

the float voltage rises to 4.1V (ADJ = floating) then Q1

and the LTC4070 shunts 192mA away from the battery.

If the battery temperature rises, the shunt current increases

to regulate the float voltage 75mV lower per 10°C rise in

battery temperature, as described in Table 1. At a maximum

shunt current of 200mA the minimum float voltage is held

at 3.8V when the battery temperature is above 70°C.

This example illustrates an alternative use of a LED, D1, to

observe the HBO status pin. This LED turns on to provide

a visual indication that the battery is fully charged, and

shunts about 1.5mA when the battery rises to within 40mV

of the desired float voltage. LED D1 discharges the battery,

LED with the HBO pin in this configuration, it is important

be selected to meet the following relation:

(

margin of 50mV is subtracted from the HBO hysteresis.

to the LED data sheet for the forward voltage drop at the

applied current level.

Figure 8. Replace Three NiMH with Lithium

4070 TA01a

LTC4070

ADJ

FLOAT

LBO

HBO

GND

T

10k

Li-Ion

NTCBIAS

DRV

NTC

+

Q1

DMP3015LSS