LTM8061EV-8.4#PBF Datasheet LTM8061IV-4.2#PBF, LTM8061EV-4.2#PBF, LTM8061EV-8.2#PBF | P13-P15

LTM8061

8061fa

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Figure 4. LTM8061 Input Current vs System

Load Current with 1.5A Input Current Limit

8061 F04

SYSTEM LOAD

CURRENT

LTM8061 INPUT

CURRENT (I

VIN

)

1.5A

1.0A

0.5A

applicaTions inForMaTion

A 1.5A system limit, for example, would use a 33mΩ sense

resistor. Figure 4 gives an example of the system current

for the situation where the input current happens to be

1A, and then gets reduced as the additional system load

increases beyond 0.5A. The LTM8061 integrates the CLP

signal internally, so average current limiting is performed

in most cases without the need for external filter elements.

For example, to reduce the maximum charge current to

50% of the original value, set RNG/SS to 0.5V. The neces

sary resistor value is:

RNG/SS

= 0.5V/50µA = 10kΩ

This feature could be used, for example, to switch in a

reduced charge current level. Applying an active voltage

can also be used to control the maximum charge current

but only if the voltage source can sink current. Figures 5

and 6 give two examples of circuits that control the charg

ing current by sinking current. Active circuits that source

current cannot be used to drive the RNG/SS pin. Care

must be taken not to exceed the 2.5V absolute maximum

voltage on the pin.

RNG/SS

8061 F05

LTM8061

LOGIC HIGH = HALF CURRENT

10k

RNG/SS

8061 F06

LTM8061

SERVO REFERENCE

–

Figure 5. Using the RNG/SS Pin for Digital Control of

Maximum Charge Current

Figure 6. Driving the RNG/SS Pin with a

Current-Sink Active Servo Amplifier

RNG/SS: Dynamic Charge Current Adjust

The LTM8061 gives the user the capability to reduce the

maximum charge current dynamically through the RNG/

SS pin. The maximum charge current of the LTM8061 is

2A and the control voltage range on the RNG/SS pin is

1V, so the maximum charge current can be expressed as:

BAT

= 2A • V

RNG/SS

where I

BAT

is the maximum charge current and V

RNG/SS

between 0V to 1V. Voltages higher than 1V have no effect

on the maximum charge current.

The LTM8061 sources 50µA from the RNG/SS pin, such

that a current control voltage can be set by simply connect

ing an appropriately valued resistor to ground, following

the equation:

RNG/SS

= V

RNG/SS

/50µA

LTM8061

8061fa

For more information www.linear.com/LTM8601

applicaTions inForMaTion

RNG/SS: Soft-Start

Soft-start functionality is also supported by the RNG/SS

pin. 50µA is sourced from the RNG/SS pin, so connect

ing a capacitor from the RNG/SS pin to ground (C

RNG/SS

in Figure 7) creates a linear voltage ramp. The maximum

charge current follows this voltage. Thus, the charge cur

rent increases from zero to the fully programmed value as

the capacitor charges from 0V to 1V. The value of C

RNG/

is calculated based on the desired time to full current

) following the equation:

RNG/SS

= 50µA • t

The RNG/SS pin is pulled to ground internally when charg-

ing terminates so each new charge cycle begins with a

soft-start cycle. RNG/SS is also pulled to ground during

bad-battery and NTC fault conditions, producing a graceful

recovery from a fault.

If the battery is removed from an LTM8061 charger that is

configured for C/10 termination, a low amplitude sawtooth

waveform appears at the charger output, due to cycling

between termination and recharge events. This cycling

results in pulsing at the CHRG output. An LED connected

to this pin will exhibit a blinking pattern, indicating to

the

user that a battery is not present. The frequency of this

blinking pattern is dependent on the output capacitance.

C/10 Termination

The LTM8061 supports a low current based termination

scheme, where a battery charge cycle terminates when

the charge current falls below one-tenth the programmed

charge current, or about 200mA. This termination mode

is engaged by shorting the TMR pin to ground. When

C/10 termination is used, an LTM8061 charger sources

battery charge current as long as the average current level

remains above the C/10 threshold. As the full-charge float

voltage is achieved, the charge current falls until the C/10

threshold is reached, at which time the charger terminates

and the LTM8061 enters standby mode. The CHRG status

is high impedance when the charger is sourcing less than

C/10. There is no provision for bad-battery detection if

C/10 termination is used.

Timer Termination

The LTM8061 supports a timer-based termination scheme,

where a battery charge cycle terminates after a specific

amount of time elapses. Timer termination is enabled

by connecting a capacitor (C

TIMER

) from the TMR pin to

GND. The timer cycle time span (t

EOC

) is determined by

TIMER

in the equation:

TIMER

= t

EOC

• 2.27 • 10

–7

(Hours)

When charging at a 1C rate, t

EOC

is commonly set to three

hours, which requires a 0.68μF capacitor.

The CHRG status pin continues to signal charging, regard

less of which termination scheme is used. When timer

termination is used, the CHRG status pin is pulled low

during a charge cycle until the charge current falls below

the C/10 threshold. The charger continues to top off the

battery until timer EOC, when the LTM8061 terminates

the charge cycle and enters standby mode.

RNG/SS

8061 F07

LTM8061

RNG/SS

Figure 7. Using the RNG/SS Pin for Soft-Start

Status Pins

The LTM8061 reports charger status through two open-

collector outputs, the CHRG and FAULT pins. These pins can

accept voltages as high as V

, and can sink up to 10mA

when enabled. The CHRG pin indicates that the charger is

delivering current at greater than a C/10 rate, or one-tenth

of the programmed charge current. The FAULT pin signals

bad-battery and NTC faults. These pins are binary coded

as shown in Table 2:

Table 2. Status Pin State

CHRG FAULT STATUS

High High Standby, Shutdown Mode, or Charging at

Less than C/10

High Low Bad-Battery Fault (Precondition Timeout/

EOC Failure)

Low High Normal Charging at C/10 or Greater

Low Low NTC Fault (Pause)

LTM8061

8061fa

For more information www.linear.com/LTM8601

applicaTions inForMaTion

Termination at the end of the timer cycle only occurs if the

charge cycle was successful. A successful charge cycle

occurs when the battery is charged to within 2.5% of the

full-charge float voltage. If a charge cycle is not success

ful at EOC, the timer cycle resets and charging continues

for another full timer cycle. When V

BAT

drops 2.5% from

the full-charge float voltage, whether by battery loading

or replacement of the battery, the charger automatically

resets and starts charging.

Preconditioning and Bad-Battery Fault

The LTM8061 has a precondition mode, in which charge

current is limited to 15% of the maximum charge current,

roughly 300mA. Precondition mode is engaged if the volt

age on the BAT pin is below the precondition threshold,

or approximately 70% of the float voltage. Once the BAT

voltage rises above the precondition threshold, normal

full-current charging can commence. The LTM8061

incorporates 90mV hysteresis to avoid spurious mode

transitions.

Bad-battery detection is engaged when using timer termina

tion. This fault detection feature is designed to identify failed

cells. A bad-battery fault is triggered when the voltage on

BAT remains below the precondition threshold for greater

than one-eighth of a

full timer cycle (one-eighth EOC). A

bad-battery fault is also triggered if a normally charging

battery re-enters precondition mode after one-eighth EOC.

When a bad-battery fault is triggered, the charge cycle

is suspended, and the CHRG status pin becomes high

impedance. The FAULT pin is pulled low to signal that a

fault has been detected. The RNG/SS pin is also pulled

low during this fault to accommodate a graceful restart

in the event that a soft-start function is incorporated (see

the RNG/SS: Soft-Start section).

Cycling the charger’s power or shutdown function initiates

a new charge cycle, but the LTM8061 charger does not

require a manual reset. Once a bad-battery fault is detected,

a new timer charge cycle initiates if the BAT pin exceeds

the precondition threshold voltage. During a bad-battery

fault, a small current is sourced from the charger; removing

the failed battery allows the charger output voltage to rise

above the preconditioning threshold voltage and initiate a

charge cycle reset. A new charge cycle is started by con

necting another battery to the charger output.

Battery Temperature Fault: NTC

The LTM8061 can accommodate battery temperature

monitoring

by using an NTC (negative temperature coef-

ficient) thermistor close to the battery pack. The tem-

perature monitoring function is enabled by connecting

a 10kΩ, β = 3380 NTC thermistor from the NTC pin to

ground. If the NTC function is not desired, leave the pin

unconnected. The NTC pin sources 50µA, and monitors

the voltage dropped across the 10kΩ thermistor. When the

voltage on this pin is above 1.36V (0°C) or below 0.29V

(40°C), the battery temperature is out of range, and the

LTM8061 triggers an NTC fault. The NTC fault condition

remains until the voltage on the NTC pin corresponds to

a temperature within the 0°C to 40°C range. Both hot and

cold thresholds incorporate 20% hysteresis, which equates

to about 5°C. If higher operational charging temperatures

are desired, the temperature range can be expanded by

adding series resistance to the 10k NTC resistor. Adding

a 909Ω resistor will increase the effective temperature

threshold to 45°C, for example.

During an NTC fault, charging is halted and both status

pins are pulled low. If timer termination is enabled, the

timer count is suspended and held until the fault condition

is cleared. The RNG/SS pin is also pulled low during this

fault to accommodate a graceful restart in the event that

a soft-start function is being incorporated (see the RNG/

SS: Soft-Start section).

Thermal Foldback

The LTM8061 contains a thermal foldback protection fea

ture that reduces charge current as the internal temperature

approaches 125°C. In most cases, internal temperatures

servo such that any overtemperature conditions are relieved

with only slight reductions in maximum charge current.

In some cases, the thermal foldback protection feature

can reduce charge currents below the C/10 threshold. In

applications that use C/10 termination (TMR = 0V), the

LTM8061 will suspend charging and enter standby mode

until the overtemperature condition is relieved.

PCB Layout

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P22

LTM8061EV-8.4#PBF

Mfr. #:

Buy LTM8061EV-8.4#PBF

Manufacturer:

Analog Devices / Linear Technology

Description:

Battery Management 32V, 2A Module Li-Ion/ Polymer Bat Ch

Lifecycle:

New from this manufacturer.

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LTM8061EV-8.4#PBF

LTM8061EV-8.4#PBF

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