SC813ULTRT Datasheet SC813ULTRT, SC811ULTRT | P16-P18

SC811 / SC813

Applications Information (continued)

which is the safest default mode with the lowest fast-

charge current.

Enable Input

The ENB pin is a tri-level logical input that allows selection

of the following behaviors:

charging enabled with  oat-charging after ter-

mination (ENB = low range)

charging enabled with  oat-charging disabled

and battery monitoring at termination (ENB =

mid range)

charging disabled (ENB = high range).

If the ENB input voltage is permitted to  oat to mid-range,

the charger is enabled but it will turn o its output follow-

ing charge termination and will enter the monitor state.

This state is explained in the next section. Mid-range can

be selected either by floating the input (sourcing or

sinking less than 5A) or by being externally forced such

that V

ENB

falls within the midrange limits speci ed in the

Electrical Characteristics table.

When driven low (V

ENB

< Max V

), the charger is enabled

and will continue to float-charge the battery following

termination. If the charger is already in monitor state fol-

lowing a previous termination, it will exit the monitor state

and begin  oat-charging.

When ENB is driven high (V

ENB

> Min V

), the charger is

disabled and the ENB input pin enters a high impedance

state, suspending tri-level functionality. The specified

high level input current I

is required only until a high

level is recognized by the SC811/3 internal logic. The tri-

level float circuitry is then disabled and the ENB input

becomes high impedance. Once forced high, the ENB pin

will not  oat to mid range. To restore tri-level operation,

the ENB pin must  rst be pulled down to mid or low range

(at least to V

ENB

< Max V

), then, if desired, released (by

recon guring the GPIO as an input) to select mid-range. If

the ENB GPIO has a weak pull-down when con gured as

an input, then it is unnecessary to drive ENB low to restore

tri-level operation; simply con gure the GPIO as an input.

When the ENB selection changes from high-range to mid-

or low-range, a new charge cycle begins and STATB goes

low.

•

Note that if a GPIO with a weak pull-up input con gura-

tion is used, its pull-up current will  ow from the GPIO into

the ENB pin while it is  oating to mid-range. Since the

GPIO is driving a 1V equivalent voltage source through a

resistance (looking into ENB), this current is small — pos-

sibly less than 1μA. Nevertheless, this current is drawn

from the GPIO peripheral power supply and, therefore,

from the battery after termination. (See the next section,

Monitor State.) For this reason, it is preferable that the

GPIO chosen to operate the ENB pin should provide a true

high impedance (CMOS) configuration or a weak pull-

down when con gured as an input. When pulled below

the  oat voltage, the ENB pin output current is sourced

from VIN, not from the battery.

Monitor State

If the ENB pin is  oating, the charger output and STATB pin

will turn o and the device will enter the monitor state

when a charge cycle is complete. If the battery voltage

falls below the re-charge threshold (V

- V

ReQ

) while in the

monitor state, the charger will automatically initiate a re-

charge cycle. The battery leakage current during monitor

state is no more than 1μA over temperature and typically

less than 0.1μA at room temperature.

While in the monitor state, the ENB tri-level input pin

remains fully active, and although in midrange, is sensitive

to both high and low levels. The SC811/3 can be forced

from the monitor state (no  oat-charging) directly to  oat-

charging operation by driving ENB low. This operation will

turn on the charger output, but will not assert the STATB

output. If the ENB pin is again allowed to float to mid-

range, the charger will remain on only until the output

current becomes less than the termination current, and

charging terminates. The SC811/3 turns o its charging

output and returns to the monitor state within a millisec-

ond. This forced re-charge behavior is useful for

periodically testing the battery state-of-charge and

topping-off the battery, without float-charging and

without requiring the battery to discharge to the auto-

matic re-charge voltage. ENB should be held low for at

least 1ms to ensure a successful forced re-charge.

Forced re-charge can be requested at any time during the

charge cycle, or even with no charging source present,

with no detrimental effect on charger operation. This

allows the host processor to schedule a forced re-charge

SC811 / SC813

Applications Information (continued)

at any desired interval, without regard to whether a charge

cycle is already in progress, or even whether a charging

source is present. Forced re-charge will neither assert nor

release the STATB output.

Status Output

The STATB pin is an open-drain output. It is asserted

(driven low) as charging begins after a valid charging

input is applied and the VIN voltage is greater than the

UVLO level and less than the OVP level of the selected

mode. STATB is also asserted as charging begins after the

ENB input returns to either of the enable voltage ranges

(mid or low voltage) from the disable (high voltage) range.

STATB is subsequently released when the termination

current is reached to indicate end-of-charge, when the

ENB input is driven high to disable charging, or when the

input voltage is removed. If the battery is already fully

charged when a charge cycle is initiated, STATB is asserted,

and will remain asserted for approximately 750µs before

being released. The STATB pin is not asserted for auto-

matic re-charge cycles.

The STATB pin may be connected to an interrupt input to

notify a host controller of the charging status or it can be

used as an LED driver.

Logical CC-to-CV Transition

The SC811/3 di ers from monolithic linear single cell Li-

ion chargers that implement a linear transition from CC to

CV regulation. The linear transition method uses two

simultaneous feedback signals — output voltage and

output current — to the closed-loop controller. When the

output voltage is sufficiently below the CV regulation

voltage, the in uence of the voltage feedback is negligible

and the output current is regulated to the desired current.

As the battery voltage approaches the CV regulation

voltage (4.2V), the voltage feedback signal begins to in u-

ence the control loop, which causes the output current to

decrease although the output voltage has not reached

4.2V. The output voltage limit dominates the controller

when the battery reaches 4.2V and eventually the control-

ler is entirely in CV regulation. The soft transition

e ectively reduces the charge current below that which is

permitted for a portion of the charge cycle, which increases

charge time.

In the SC811/3, a logical transition is implemented from

CC to CV to recover the charge current lost due to the soft

transition. The controller regulates only current until the

output voltage exceeds the transition threshold voltage.

It then switches to CV regulation. The transition voltage

from CC to CV regulation is typically 5mV higher than the

CV regulation voltage, which provides a sharp and clean

transition free of chatter between regulation modes. The

di erence between the transition voltage and the regula-

tion voltage is termed the CC/CV overshoot. While in CV

regulation, the output current sense remains active. If the

output current exceeds by 5% the mode-dependent pro-

grammed fast-charge current, the controller reverts to

current regulation.

The logical transition from CC to CV results in the fastest

possible charging cycle that is compliant with the speci-

 ed current and voltage limits of the Li-ion cell. The output

current is constant at the CC limit, then decreases abruptly

when the output voltage steps from the overshoot voltage

to the regulation voltage at the transition to CV control.

Thermal Limiting

Device thermal limiting is the third output constraint of

the Constant Current, Constant Voltage, “Constant”

Temperature (CC/CV/CT) control. This feature permits a

higher input OVP threshold, and thus the use of higher

voltage or poorly regulated adapters. If high input voltage

results in excessive power dissipation, the output current

is reduced to prevent overheating of the SC811/3. The

thermal limiting controller reduces the output current by

≈ 50mA/ºC for any junction temperature T

> T

When thermal limiting is inactive,

= T

+ V



where V



is the voltage difference between the VIN pin

and the BAT pin. However, if T

computed this way exceeds

, then thermal limiting will become active and the

thermal limiting regulation junction temperature will be

JTL

= T

+ V



I(T

JTL

) θ

where

I(T

JTL

) = I

− i

JTL

− T

SC811 / SC813

Applications Information (continued)

Combining these two equations and solving for T

JTL

, the

steady state junction temperature during active thermal

limiting is





JAT

JATLTx_FQA

JTL

iV1

TiIVT









Although the thermal limiting controller is able to reduce

output current to zero, this does not happen in practice.

Output current is reduced to I(T

JTL

), reducing power dissi-

pation such that die temperature equilibrium T

JTL

reached.

While thermal limiting is active, all charger functions

remain active and the charger logical state is preserved.

Operating a Charging Adapter in Current Limit

In high charging current applications, charger power dis-

sipation can be greatly reduced by operating the charging

adapter in current limit. The SC811/3 adapter mode sup-

ports adapter-current-limited charging with a low UVLO

falling threshold and with internal circuitry designed for

low input voltage operation. To operate an adapter in

current limit, R

IPRGM

is chosen such that the adapter input

programmed fast-charge current I

FQ_AD

exceeds the current

limit of the charging adapter I

AD-LIM

Note that if I

AD-LIM

is less than 20% of I

FQ_AD

, then the adapter

voltage can be pulled down to the battery voltage while

the battery voltage is below the pre-charge threshold. In

this case, care must be taken to ensure that the adapter

will maintain its current limit below 20% of I

FQ_AD

at least

until the battery voltage exceeds the pre-charge thresh-

old. Failure to do so could permit charge current to exceed

the pre-charge current while the battery voltage is below

the pre-charge threshold. This is because the low input

voltage will also compress the pre-charge threshold inter-

nal reference voltage to below the battery voltage. This

will prematurely advance the charger logic from pre-

charge current regulation to fast-charge regulation, and

the charge current will exceed the safe level recom-

mended for pre-charge conditioning.

The low UVLO falling threshold (

ADUVLO-F

) permits the

adapter voltage to be pulled down to just above the

battery voltage by the charging load whenever the

adapter current limit is less than the programmed fast-

charge current. The SC811/3 should be operated with

adapter voltage below the rising selection threshold

(VT

ADUVLO-R

) only if the low input voltage is the result of

adapter current limiting. This implies that the VIN voltage

first exceeds

ADUVLO-R

to begin charging and is subse-

quently pulled down to just above the battery voltage by

the charging load.

Interaction of Thermal Limiting and Current Limited

Adapter Charging

To permit the charge current to be limited by the adapter,

it is necessary that the adapter mode fast-charge current

be programmed greater than the maximum adapter

current, (I

AD-LIM

). In this con guration, the CC regulator will

operate with its pass device fully on (in saturation, also

called “dropout”). The voltage drop from VIN to BAT is

determined by the product of the minimum R

DS-ON

of the

pass device multiplied by the adapter supply current.

In dropout, the power dissipation in the SC811/3 is

ILIM

= (minimum R

DS-ON

) x (I

AD-LIM

)

. Since minimum R

DS-ON

does not vary with battery voltage, dropout power dissi-

pation is constant throughout the CC portion of the

charge cycle while the adapter remains in current limit.

The SC811/3 junction temperature will rise above ambient

by P

ILIM

x θ

. If the device temperature rises to the tem-

perature at which the thermal limiting control loop limits

charging current (rather than the current being limited by

the adapter), the input voltage will rise to the adapter

regulation voltage. The power dissipation will increase so

that the thermal limit regulation will further limit charge

current. This will keep the adapter in voltage regulation

for the remainder of the charge cycle.

To ensure that the adapter remains in current limit, the

internal device temperature must never rise to T

. This

implies that θ

must be kept small enough to ensure that

= T

+ (P

ILIM

× θ

) < T

Under-Voltage Load Regulation in USB Modes

VIN pin UVLR in either USB mode prevents the battery

charging current from overloading the USB Vbus network,

regardless of the programmed fast-charge value. When

USB High Power or USB Low Power mode is selected, the

SC811/3 monitors the input voltage (V

VIN

) and reduces the

charge current as necessary to keep V

VIN

at or above the

UVLR limit (V

UVLR

). UVLR operates like a fourth output con-

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P23

SC813ULTRT

Mfr. #:

Buy SC813ULTRT

Manufacturer:

Semtech

Description:

Battery Management DUAL INPUT LITH ION BAT CHRG

Lifecycle:

New from this manufacturer.

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SC813ULTRT

SC813ULTRT

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