SC813ULTRT Datasheet SC813ULTRT, SC811ULTRT | P19-P21

SC811 / SC813

Applications Information (continued)

straint (along with CC, CV, and CT constraints), but it is

active only when one of the USB modes is selected.

In either of the USB modes, if the VIN voltage is externally

pulled below V

UVLR

, the UVLR feature will reduce the charg-

ing current to zero. This condition will not be interpreted

as termination and will not result in an end-of-charge indi-

cation. The STATB pin will remain asserted as if charging is

continuing. This behavior prevents repetitive indications

of end-of-charge alternating with start-of-charge in the

case that the external VIN load is removed or is

intermittent.

USB High Power and Low Power Support

The USB speci cation restricts the load on the USB Vbus

power network to 100mA for low power devices and for

high power devices prior to granting permission for high

power operation. The speci cation restricts the Vbus load

to 500mA for high power devices after granting permis-

sion to operate as a high power device. A  xed 1:5 ratio of

low power to high power charging current is desirable for

charging batteries with maximum fast-charge current of

at least 500mA. For this application, the SC811/3 provides

 xed 1:5 current ratio low-to-high power mode support,

via the tri-level MODE input pin.

For batteries with maximum fast-charge current less than

500mA, a  xed 1:5 low/high power charge current ratio

will result in suboptimal charging in USB low power mode.

For example, a 250mAh battery will typically require a

fast-charge current of 250mA or less. A  xed 1:5 ratio for

USB low-to-high power charging current will unnecessar-

ily reduce charging current to 50mA, well below the

100mA permitted. In this case, it may be preferable to

program USB low-power fast-charge current by switching

an external programming resistor. See the section Design

Considerations — Small Battery.

Input Over-Voltage Protection

The VIN pin is protected from over-voltage to at least 30V

above GND. When the input voltage exceeds the Over-

Voltage Protection (OVP) rising threshold (VT

OVP-R

charging is halted. When the input voltage falls below the

OVP falling threshold (VT

OVP-F

), charging restarts. An OVP

fault turns o the STATB output. STATB is turned on again

when charging restarts.

The OVP threshold of the SC811 has been set relatively

high to permit the use of poorly regulated adapters. Such

adapters may output a high voltage until loaded by the

charger. A too-low OVP threshold could prevent the

charger from ever turning on and loading the adapter to

a lower voltage. If the adapter voltage remains high

despite the charging load, the fast thermal limiting feature

will immediately reduce the charging current to prevent

overheating of the SC811. This behavior is illustrated in

Figure 4, in which V

BAT

= 3.0V, I

= 700mA, and V

VIN

stepped from 0V to 8.1V. Initially, power dissipation in the

SC811 is 3.6W.

1s/div

VIN

(2V/div)

VIN

BAT

=0V—

BAT

(100mA/div)

BAT

=0mA—

VIN

=8.1V, V

BAT

=3.0V

BAT

=700mA (Initially), P

DISSIPATION

=3.6W (Initially)

BAT

(2V/div)

Figure 4 — SC811 Thermal Limiting Example

Notice the BAT output current is rapidly reduced to limit

the internal die temperature, then continues to decline as

the circuit board gradually heats up, further reducing the

conduction of heat from the die to the ambient environ-

ment. The fast thermal limiting feature ensures compliance

with CCSA YD/T 1591-2006, Telecommunication Industrial

Standard of the People’s Republic of China — Technical

Requirements and Test Method of Charger and Interface for

Mobile Telecommunication Terminal, Section 4.2.3.1.

Alternatively, the SC813 is o ered for users who want to

limit OVP to a guaranteed maximum of 6V. The SC811 and

SC813 are alike except for OVP threshold.

Short Circuit Protection

The SC811/3 can tolerate a BAT pin short circuit to ground

inde nitely. The current into a ground short is approxi-

mately 10mA.

SC811 / SC813

During charging, a short to ground applied to the active

current programming pin (IPRGM or IPUSB) is detected,

while a short to ground on the inactive programming pin

is ignored. Pin-short detection on an active current pro-

gramming pin forces the SC811/3 into reset, turning o

the output. A pin-short on either programming pin will

prevent startup regardless of the mode selected. When

the IPRGM or IPUSB pin-short condition is removed, the

charger begins normal operation automatically without

input power cycling.

Over-Current Protection

Over-current protection is provided in all modes of opera-

tion, including CV regulation. The output current is limited

to either the programmed pre-charge current limit value

or the fast-charge current limit value, depending on the

voltage at the output.

Operation Without a Battery

The SC811/3 can be operated as a 4.2V LDO regulator

without the battery present, for example, factory testing.

If this use is anticipated, the output capacitance C

BAT

should be at least 2.2F to ensure stability. To operate the

charger without a battery, the ENB pin must be driven low

or grounded.

Capacitor Selection

Low cost, low ESR ceramic capacitors such as the X5R and

X7R dielectric material types are recommended. The BAT

pin capacitor range is 1F to 22F. The VIN pin capacitor

is typically between 0.1F and 2.2F, although larger

values will not degrade performance. Capacitance must

be evaluated at the expected bias voltage, rather than the

zero-volt capacitance rating.

PCB Layout Considerations

Layout for linear devices is not as critical as for a switching

regulator. However, careful attention to detail will ensure

reliable operation.

Place input and output capacitors close to the

device for optimal transient response and device

behavior.

Connect all ground connections directly to the

ground plane. If there is no ground plane,

connect to a common local ground point before

connecting to board ground near the GND pin.

•

Attaching the part to a larger copper footprint

will enable better heat transfer from the device,

especially on PCBs with internal ground and

power planes.

Design Considerations — Large Battery

A battery with a desired fast-charge current exceeding

500mA is most consistent with the USB  xed 1:5 current

ratio low-to-high power model of operation. For example,

consider an 800mAh battery, with maximum fast-charge

current of 800mA. The adapter input fast-charge should

be configured for 800mA max (R

IPRGM

= 2.80k). Select

IPUSB

= 4.53k to set USB high power fast-charge to

450mA, and the USB low power fast-charge set to

450/5 = 90mA. The MODE pin tri-level logical input can be

used to select between USB high power and USB low

power modes whenever a fixed 5:1 current ratio is

desired.

Design Considerations — Small Battery

A battery with a desired fast-charge current less than

500mA will not be charged in minimum charge time when

in USB low power mode of operation with a 1:5 low-to-

high power mode current ratio. A 300mAh battery can be

used as an example with maximum fast-charge current of

300mA. In this example, the adapter input and USB input

high power fast-charge currents should both be set to

300mA. The USB low power fast-charge current of, for

example, 90mA, for a low-to-high power current ratio of

1:3.3, would provide a shorter charge time than the 60mA

obtained with the  xed USB low-to-high power charging

current ratio of 1:5.

An arbitrary ratio of USB low-to-high power charging cur-

rents can be obtained using an external n-channel FET

operated with a processor GPIO signal to engage a second

parallel IPUSB resistor, while selecting high power mode

(MODE pin driven high) for both low or high power charg-

ing. The external circuit is illustrated in Figure 5.

IPUSB

IPUSB_HI

USB Hi/Lo

Power Select

Figure 5. External programming of arbitrary USB high

power and low power charge currents.

•

Applications Information (continued)

SC811 / SC813

For USB low power mode charging, the external transistor

is turned o . The transistor is turned on when high power

mode is desired. The e ect of the switched parallel IPUSB

resistor is to reduce the e ective programming resistance

and thus raise the fast-charge current.

An open-drain GPIO can be used directly to engage the

parallel resistor R

IPUSB_HI

. Care must be taken to ensure that

the R

DS-ON

of the GPIO is considered in the selection of

IPUSB_HI

. Also important is the part-to-part and tempera-

ture variation of the GPIO R

DS-ON

, and their contribution to

the USB High Power charge current tolerance. Note also

that IPUSB will be pulled up brie y to as high as 3V during

startup to check for an IPUSB static pinshort to ground. A

small amount of current could, potentially, flow from

IPUSB into the GPIO ESD structure through R

IPUSB_HI

during

this event. While unlikely to do any harm, this e ect must

also be considered.

The 300mAh battery example can be used to illustrate

how this system works. The adapter mode and USB high

power mode fast-charge currents should both be set to

300mA max. The USB input low power fast-charge current

is 100mA max. Refer to the circuit in Figure 5 and the data

of Figures 1a and 1b. For I

FQ_AD

= 300mA max, use R

IPRGM

7.50k. A  xed IPUSB resistor of R

IPUSB

= 23.2k programs

FQ_USB

= 100mA max for USB low power charging. When a

parallel resistor R

IPUSB_HI

= 11.0k resistor is switched in, the

equivalent IPUSB resistor is 7.50k, for I

FQ_USB

= 300mA

max.

USB Low Power Mode Alternative

Where a USB mode selection signal is not available, or for

a low capacity battery where system cost or board space

make USB low power mode external current program-

ming impractical, USB low power charging can be

supported indirectly. The IPUSB pin

resistance can be

selected to obtain the desired USB high power charge

current. Then, with the MODE pin always con gured for

USB high power mode, the UVLR feature will ensure that

the charging load on the VIN pin will never pull the USB

Vbus supply voltage below V

UVLR

regardless of the host or

hub supply limit. The UVLR limit voltage guarantees that

the voltage of the USB Vbus supply will not be loaded

below the low power voltage speci cation limit, as seen

by any other low power devices connected to the same

USB host or hub.

Independent Programming of Termination

Current

The USB high power mode fast-charge current is limited

to 1000mA, twice the USB high power load limit, and so

this mode may also be used for general purpose adapter

charging. The IPRGM pin resistance to ground determines

the USB high power mode pre-charge current, and the

termination threshold current for all modes. If adapter

mode will not be used in the application, R

IPRGM

can be

selected to program only the termination threshold

current independently of the fast-charge current, which is

programmed with R

IPUSB

Note that USB high power mode invokes Under-Voltage

Load Regulation, so if charging with an adapter in current

limit, the input voltage can be pulled down no lower than

UVLR

USB-only Charging of Very Large Batteries

The SC811/3 can support the charging of very large capac-

ity batteries as high as 2Ah using a USB-only charging

source. The IPRGM resistance lower limit of 2.05k is

intended to limit the fast-charge current while charging in

adapter mode to less than 1A. If only USB charging modes

will be used, then the IPRGM resistor can be chosen as low

as 1k. This extended programming range allows setting

the USB high power mode pre-charge current as high as

400mA (still below the USB speci cation limit), and the

charge termination current as high as 200mA. (Both of

these currents are determined by R

IPRGM

.) Note that with

IPRGM

< 2.05k, adapter mode should not be used, as this

can result in potentially destructive fast-charge current.

The USB high power and USB low power fast-charge cur-

rents and the USB low power pre-charge current are

determined by the resistance between IPUSB and GND to

comply with USB speci ed current limits, and so are unaf-

fected by the IPRGM resistor. Termination detection

requires that the charger be in CV regulation. If the

IPRGM-determined termination threshold current is set

higher than the USB low power mode fast-charge current,

for example, then charge termination will occur the instant

that the battery voltage rises to V

. Thus USB low power

charging will behave as if trickle-charging until fully

charged, a perfectly safe and acceptable, although slow,

charging scenario.

Applications Information (continued)

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

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SC813ULTRT

SC813ULTRT

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