SC820

SC820 SEMTECH | Alldatasheet

Document overview

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Technical content

Features

Dual input charger automatically selects adapter input over USB Constant voltage — 4.2V, 1% regulation Fast-charge current regulation — 15% at 70mA, 9% at 700mA Three mode charging (current regulation, voltage regulation, thermal limiting) Input voltage protection — 30V Current-limited adapter charging support — reduces power dissipation in charger USB input limits charge current to prevent Vbus overload Instantaneous CC-to-CV transition for faster charging Programmable battery-dependent currents (adapter- sourced fast-charge & pre-charge, termination) Programmable source-limited currents (USB-sourced fast-charge & pre-charge) Three termination options — fl oat-charge, automatic re-charge, or forced re-charge to keep the battery topped-off after termination without fl oat-charging Soft-start reduces adapter or USB load transients High operating voltage range permits use of unregulated adapters Complies with CCSA YD/T 1591-2006 Space saving 2x2x0.6 (mm) MLPD package WEEE and RoHS compliant

Applications

Description

The SC820 is a dual input (adapter/USB) linear single-cell Li-ion battery charger in an 8 lead 2x2 MLPD ultra-thin package. Both inputs will survive sustained input voltage up to 30V to protect against hot plug overshoot and faulty charging adapters. Charging begins automatically when a valid input source is applied to either input. The adapter input is selected when both input sources are present. Thermal limiting protects the SC820 from excessive power dissipation when charging from either source. The SC820 can be programmed to turn off when charging is complete or to continue operating as an LDO regulator while fl oat- charging the battery. The adapter input charges with an adapter operating in voltage regulation or in current limit to obtain the lowest possible power dissipation by pulling the VAD input voltage down to the battery voltage. The VUSB input automatically limits load current to prevent over-loading the USB Vbus supply. Charge current programming requires two resistors. One determines battery-capacity dependent currents: adapter input fast-charge current, pre-charge current, and charge termination current. The other independently determines input-limited USB charging currents: USB input fast- charge and pre-charge current. Device Load Battery Pack 2.2 μF USB Vbus 2.2 μF VADAPTER 2.2 μF IPUSB IPRGM VUSB SC820 GND STATB ENB BAT VAD Typical Application Circuit February 26, 2008

Ordering Information

SC820ULTRT(1)(2) MLPD-UT-8 2×2 SC820EVB Evaluation Board Notes: (1) Available in tape and reel only. A reel contains 3,000 devices. (2) Lead-free package only. Device is WEEE and RoHS compliant. TOP VIEW T 4 5

8 ENB

MLPD-UT8; 2x2, 8 LEAD θJA = 68°C/W yw = Date Code

Exceeding the above specifi cations may result in permanent damage to the device or device malfunction. Operation outside of the parameters specifi ed in the Electrical Characteristics section is not recommended. NOTES: (1) Tested according to JEDEC standard JESD22-A114-B. (2) Calculated from package in still air, mounted to 3 x 4.5 (in), 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards. Absolute Maximum Ratings BAT +0.3 ESD Protection Level Recommended Operating Conditions Thermal Information Test Conditions: VVAD = VVUSB = 4.75V to 5.25V; VBAT = 3.7V; Typ values at 25°C; Min and Max at -40°C < TA < 85°C, unless specifi ed. Parameter Symbol Conditions Min Typ Max Units VAD Operating Voltage (1) VAD-OP 4.60 5.00 8.20 V VAD Select Rising Threshold VT ADsel-R 4.30 4.45 4.60 V VAD Deselect Falling Threshold (2) VTADsel-F VVAD > VBAT 2.70 2.85 3.00 V USB Input Operating Voltage (1) VUSB-OP 4.35 5.00 8.20 V VUSB Select Rising Threshold VT USBsel-R VVUSB > VBAT 4.20 4.35 V VUSB Deselect Falling Threshold VT USBsel-F VVUSB > VBAT 3.65 4.00 V VUSB Select Hysteresis VT USBsel-H VTUSBsel-R - VTUSBsel-F 100 mV OVP Rising Threshold VT OVP-R VAD or VUSB input 9.6 V OVP Falling Threshold VT OVP-F VAD or VUSB input 8.2 V OVP Hysteresis VT OVP-H (VTOVP-R - VTOVP-F)5 0 m V VAD Charging Disabled Quiescent Current IqVAD_DIS VVUSB = 0V, VENB = VBAT 23 m A VAD Charging Enabled Quiescent Current IqVAD_EN VVUSB = 0V, VENB = 0V, excluding IBAT, IIPRGM, and IIPUSB 23 m A VUSB Charging Disabled Quiescent Current IqVUSB_DIS VVAD = 0V; VENB = VBAT 23 m A VUSB Charging Enabled Quiescent Current IqVUSB_EN VVAD = 0V, VENB = 0V, excluding IBAT, IIPRGM, and IIPUSB 23 m A

Electrical Characteristics

Parameter Symbol Conditions Min Typ Max Units VUSB Deselected Quiescent Current(3) IqVUSB_DES VVAD ≥ VVUSB 25 50 μA CV Regulation Voltage V CV IBAT = 50mA, -40°C ≤ TJ ≤ 125°C 4.16 4.20 4.24 V CV Voltage Load Regulation(4) VCV_LOAD Relative to VCV @ 50mA, VVAD = 5V, or VVUSB = 5V and VVAD = 0V, 1mA ≤ IBAT ≤ 700mA, -40°C ≤ TJ ≤ 125°C -20 10 mV Re-charge Threshold VT ReQ VCV — VBAT 60 100 140 mV Pre-charge Threshold (rising) VT PreQ 2.85 2.90 2.95 V Battery Leakage Current lBAT_V0 VBAT = VCV, VVAD = VVUSB = 0V 0.1 1 μA lBAT_DIS VBAT = VCV, VVAD = VVUSB = 5V, VENB = 2V 0.1 1 μA lBAT_MON VBAT = VCV, VVAD = VVUSB = 5V, ENB not connected 0.1 1 μA IPRGM Programming Resistor R IPRGM 2.05 29.4 kΩ Fast-Charge Current, VAD input I FQ_AD RIPRGM = 2.94kΩ, VTPreQ < VBAT < VCV 643 694 745 mA Pre-Charge Current, VAD input I PreQ_AD RIPRGM = 2.94kΩ, 1.8V < VBAT < VTPreQ 105 139 173 mA Termination Current, either input I TERM RIPRGM = 2.94kΩ, VBAT = VCV 59 69 80 mA VAD to BAT Dropout Voltage V DO_AD IBAT = 700mA, 0°C ≤ TJ ≤ 125°C 0.75 1.0 V IPUSB Programming Resistor R IPUSB 2.05 29.4 kΩ Fast-Charge Current, VUSB input I FQ_USB RIPUSB = 4.42kΩ, VTPreQ < VBAT < VCV 427 462 497 mA Pre-Charge Current, VUSB input I PreQ_USB RIPUSB = 4.42kΩ, 1.8V < VBAT < VTPreQ 69 92 116 mA VUSB to BAT Dropout Voltage V DO_USB IBAT = 500mA, 0°C ≤ TJ ≤ 125°C 0.55 1 V IPRGM Fast-charge Regulated Voltage V IPRGM_FQ VVAD = 5.0V, VVUSB = 0V, VTPreQ < VBAT < VCV 2.04 V IPRGM Pre-charge Regulated Voltage V IPRGM_PQ VBAT < VTPreQ 0.408 V IPRGM Termination Threshold Voltage VT IPRGM_TERM VBAT = VCV (either input selected) 0.204 V IPUSB Fast-charge Regulated Voltage V IPUSB_FQ VVAD = 0V, VTPreQ < VBAT < VCV 2.04 V IPUSB Pre-charge Regulated Voltage V IPUSB_PQ VVAD = 0V, VBAT < VTPreQ 0.408 V VUSB Under-Voltage Load Regulation Limiting Voltage VVUSB_UV_LIM 5mA ≤ VUSB supply current limit ≤ 500mA, VVAD = 0V, RIPUSB = 3.65kΩ (559mA) 4.45 4.58 4.70 V Electrical Characteristics (continued)

Electrical Characteristics (continued) Parameter Symbol Conditions Min Typ Max Units Thermal Limiting Threshold Temperature TTL 130 °C Thermal Limiting Rate i T 50 mA/ °C ENB Input High Voltage V IH 1.6 V ENB Input Mid Voltage V IM 0.7 1.3 V ENB Input Low Voltage V IL 0.3 V ENB Input High-range Threshold Input Current IIH_TH ENB current required to pull ENB from floating midrange into high range 23 50 μA ENB Input High-range Sustain Input Current IIH_SUS Current required to hold ENB in high range, Min VIH ≤ VENB ≤ VBAT, Min VIH ≤ VBAT ≤ 4.2V 0.3 1 μA ENB Input Mid-range Load Limit I IM Input will float to mid range when this load limit is observed. -5 5 μA ENB Input Low-range Input Current I IL 0V ≤ VENB ≤ Max VIL -25 -12 μA ENB Input Leakage I ILEAK VVIN = 0V, VENB = VBAT = 4.2V 1 μA STATB Output Low Voltage V STAT_LO ISTAT_SINK = 2mA 0.5 V STATB Output High Current I STAT_HI VSTAT = 5V 1 μA Notes: (1) Maximum operating voltage is the maximum Vsupply as defined in EIA/JEDEC Standard No. 78, paragraph 2.11. This is the inpu t voltage at which the charger is guaranteed to begin operation. (2) Sustained operation to VT ADsel-F ≤ VVAD is guaranteed only if a current limited charging source applied to VAD is pulled below VT ADsel-R by the charging load; forced VAD voltage below VTADsel-R may in some cases result in regulation errors or other unexpected behavior. (3) If VAD is the selected input but V VAD < VVUSB, such as when VAD is operating with an adapter in current limit while a VUSB charging source is applied, IqVUSB_DES will increase to approximately IqVUSB_EN. (4) At load currents exceeding 700mA, or at 700mA while at elevated ambient temperature, the charger may enter dropout with a 5V input before the battery voltage has risen to VCV. See the specifi cation of VDO_AD. Although this is a safe and acceptable mode of operation, specifi cation of VCV when in dropout is not applicable; higher input voltage will restore the charger to CV regulation in these cases. Note that VBAT is always less than VCV while in dropout. As the battery state-of-charge increases, the charging current will decrease allowing the battery voltage to rise to VCV, and CV regulation will begin. This appears as a softening or rounding of the CC-to-CV regulation mode transition, similar to that seen in chargers with a linear CC-to-CV regulation crossover.

CV Line Regulation CV Load Regulation CV Temperature Regulation CC FQ Line Regulation (AD or USB) CC FQ VBAT Regulation (AD or USB) CC FQ Temperature Regulation (AD or USB) 55 . 566 . 577 . 584.18 4.184 4.188 4.192 4.196 4.2 4.204 VVAD (V) VBAT (V) TA = 25οC, IBAT = 50mA 0 100 200 300 400 500 600 700 8004.18 4.184 4.188 4.192 4.196 4.2 4.204 IBAT (mA) VBAT (V) TA = 25οC, VVAD = 5V -40 -20 0 20 40 60 80 100 1204.18 4.184 4.188 4.192 4.196 4.2 4.204 Ambient Temperature ( o VBAT (V) VVAD = 5V, IBAT = 50mA 4.5 5 5.5 6 6.5 7 7.5 8440 480 520 560 600 640 680 720 RIPRGM or RIPUSB = 2.94kΩ RIPRGM or RIPUSB = 4.42kΩ VVAD (V) IBAT (mA) TA = 25οC, VBAT = 3.7V 440 480 520 560 600 640 680 720 VBAT (V) IBAT (mA) TA = 25οC, VVAD = 5V RIPRGM or RIPUSB = 2.94kΩ RIPRGM or RIPUSB = 4.42kΩ -40 -20 0 20 40 60 80 100 120440 480 520 560 600 640 680 720 Ambient Temperature ( o IBAT (mA) VVAD = 5V, VBAT = 3.7V

Typical Characteristics (continued) CC PQ Line Regulation (AD or USB) CC PQ Temperature Regulation (AD or USB) IFQ_AD vs. RIPRGM , or IFQ_USB vs. RIPUSB IPQ_AD vs. RIPRGM , or IPQ_USB vs. RIPUSB CC — Input Reselection, AD to USB CC — Input Reselection, USB to AD 55 . 566 . 577 . 5890 100 110 120 130 140 150 160 VVAD (V) IBAT (mA) TA = 25οC, VBAT = 2.6V RIPRGM or RIPUSB = 2.94kΩ RIPRGM or RIPUSB = 4.42kΩ -40 -20 0 20 40 60 80 100 12090 100 110 120 130 140 150 160 Ambient Temperature ( o IBAT (mA) VVAD = 5V, VBAT = 2.6V RIPRGM or RIPUSB = 2.94kΩ RIPRGM or RIPUSB = 4.42kΩ 2 6 10 14 18 22 26 300 200 400 600 800 1000 RIPRGM or RIPUSB (kΩ) IBAT (mA) VVAD = 5V, VBAT = 3.7V, TA = 25οC 2 6 10 14 18 22 26 300 120 160 200 RIPRGM or RIPUSB (kΩ) IBAT (mA) VVAD = 5V, VBAT = 2.6V, TA = 25οC 400μs/div VVAD (1.0V/div) VVAD=0V— IBAT (200mA/div) IBAT=0mA— VBAT=3.7V, VVUSB=5.0V 400μs/div VVAD (1.0V/div) VVAD=0V— IBAT (200mA/div) IBAT=0mA— VBAT=3.7V, VVUSB=5.0V

Typical Characteristics (continued) Charging Cycle Battery Voltage and Current Pre-Charging Battery Voltage and Current CC-to-CV Battery Voltage and Current Re-Charge Cycle Battery Voltage and Current 100 200 300 400 500 600 700 IBAT (mA) Time (hrs) VBAT (V), Internal Power Dissipation (W) 850mAhr battery, RIPRGM = 2.94kΩ, VVAD = 5.0V, TA = 25οC VBAT IBAT 100 200 300 400 500 600 700 800 IBAT (mA) 0 2 4 6 8 1 01 21 41 61 82 02 2.25 2.5 2.75 3.25 3.5 3.75 Time (s) VBAT (V) 850mAhr battery, RIPRGM = 2.94kΩ, VVAD = 5.0V, TA = 25οC VBAT IBAT 610 630 650 670 690 710 IBAT (mA) 4.17 4.18 4.19 4.2 4.21 Time (min) VBAT (V) 850mAhr battery, RIPRGM = 2.94kΩ, VVAD = 5.0V, TA = 25οC VBAT IBAT 100 150 200 250 300 350 400 450 IBAT (mA) 0.5 1.5 2.5 3.5 4.5 Time (hrs) VBAT (V), Internal Power Dissipation (W) 850mAhr battery, RIPRGM = 2.94kΩ, VVAD = 5.0V, Load = 10mA VBAT IBAT Discharge hours 2 - 6 omitted.

Pin # Pin Name Pin Function 1V A D Supply pin — connect to charging adapter. This pin is protected against damage due to high voltage up to 30V. 2 VUSB Supply pin — connect to USB Vbus power. Typically 5V, limited load-current input. This pin is protected against damage due to high voltage up to 30V. 3S T A T B Status output pin — This open-drain pin is asserted (pulled low) when a valid charging supply is connected to either VAD or VUSB, and a charging cycle begins. It is released when the termination current is reached, indicating that charging is complete. STATB is not asserted for re-charge cycles.

4 GND Ground

5 IPUSB

Fast-charge and pre-charge current programming pin for the VUSB power source — VUSB fast-charge current is programmed by connecting a resistor from this pin to ground. VUSB pre-charge current is 20% of fast-charge current.

6 IPRGM

Fast-charge and pre-charge current programming pin for the adapter power source — VAD fast-charge current is programmed by connecting a resistor from this pin to ground. VAD pre-charge current is 20% of fast-charge current. The charging termination current threshold (for either VAD or VUSB input selection) is 10% of the IPRGM programmed fast-charge current. 7B A T Charger output — connect to battery positive terminal. Combined device enable/disable — Logic high disables the device. Tie to GND to enable charging with indefi nite fl oat-charging. Float this pin to enable charging without fl oat-charge upon termination. Note that this pin must be grounded if the SC820 is to be operated without a battery connected to BAT. T Thermal Pad Pad is for heatsinking purposes — not connected internally. Connect exposed pad to ground plane using multiple vias.

V_Adapter USB_VBUS 1 2 To System Load Lithium- Ion Single Cell Battery Pack RIPRGMRIPUSB Connect to BAT or to regulated supply VTIPRGM_TERM VCV = 4.2V VIREF VVUSB_UV_LIM = 4.575V Pre-charge, CC/ CV & Termination Controller, Logical State Machine CC Feedback Selection Tri-level Control VTENB_HIGH = ~1.50V VTENB_LOW = ~0.551V Thermal Limiting Die Temperature VT_CT

The SC820 is a dual-input stand-alone Li-ion battery charger. The VAD input pin is optimized for a charging adapter. The VUSB pin is optimized for charging from the USB Vbus supply. The device is independently pro- grammed for battery-capacity-dependent currents (adapter fast-charge current and termination current) using the IPRGM pin. Charging currents from the USB Vbus supply, which has a maximum load specifi cation, are programmed using the IPUSB pin. When an input supply is fi rst detected, a charge cycle is initiated and the STATB open-drain output goes low. If the battery voltage is less than the pre-charge threshold voltage, the pre-charge current is supplied. Pre-charge current is 20% of the programmed fast-charge current for the selected input. When the battery voltage exceeds the pre-charge thresh- old, typically within seconds for a standard battery with a starting cell voltage greater than 2V, the fast-charge Constant Current (CC) mode begins. The charge current soft-starts in three steps (20%, 60%, and 100% of pro- grammed fast-charge current) to reduce adapter load transients. CC current is programmed by the IPRGM resis- tance to ground when the VAD input is selected and by the IPUSB resistance to ground when the VUSB input is selected. The charger begins Constant Voltage (CV) regulation when the battery voltage rises to the fully-charged single- cell Li-ion regulation voltage (V CV), nominally 4.2V. In CV regulation, the output voltage is regulated, and as the battery charges, the charge current gradually decreases. The STATB output goes high when I BAT drops below the termination current threshold, which is 10% of the IPRGM pin programmed fast-charge current regardless of the input selected. This is known as charge termination. Optional Float-charging or Monitoring Depending on the state of the ENB input, upon termina- tion the SC820 either operates indefi nitely as a voltage regulator (fl oat-charging) or it turns off its output. If the output is turned off upon termination, the device enters the monitor state. In this state, the output remains off until the BAT pin voltage decreases by the re-charge threshold (VT ReQ). A re-charge cycle then begins auto- matically and the process repeats. A forced re-charge cycle can also be periodically commanded by the pro- cessor to keep the battery topped-off without fl oat-charging. See the Monitor State section for details. Re-charge cycles are not indicated by the STATB pin. Charging Input Selection The SC820 has two charging supply input pins. VAD is optimized for adapter charging. VUSB is optimized for charging from the USB Vbus power supply. The inputs diff er in selection rising and deselection falling thresh- olds, their behavior when overloading their respective charging sources, and in which current programming pin determines the fast-charge and pre-charge current. Both use the same Over-Voltage Protection (OVP) threshold. Glitch fi ltering is performed on the VAD and VUSB inputs, so an applied input voltage that is ringing across its selec- tion threshold will not be selected until the ringing has ceased. When both inputs exceed their respective UVLO thresholds, VAD is selected even when VAD voltage is applied while already charging from the VUSB input. VAD is also selected in the case that the VAD voltage exceeds its OVP threshold, so that an excessive VAD voltage will disable charging despite the presence of a valid VUSB input voltage. When a valid input (defi ned as greater than its selection threshold and less than the OVP threshold) is first selected, a charge cycle is initiated and the STATB output is asserted. When a new input selection is made (when VAD is applied or removed while VUSB is present), the charge cycle is immediately halted and re-initiated with the newly selected input. There is a momentary (approxi- mately 1ms) interruption in output current and a release and re-assertion of the STATB pin during input reselection. If the VAD input charging current loads the adapter beyond its current limit, the VAD input voltage will be pulled down to just above the battery voltage. The adapter input deselection falling threshold is set close to the battery voltage pre-charge threshold to permit low- dissipation charging from a current limited adapter. The VUSB input provides a higher deselection falling threshold appropriate to the USB specifi cation. The USB Applications Information

Applications Information (continued) level is recognized by the SC820 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 fl oat to mid range. To restore tri-level operation, the ENB pin must fi rst be pulled down to mid or low range (at least to V ENB < Max V IM), then, if desired, released (by reconfi guring the GPIO as an input) to select mid-range. If the ENB GPIO has a weak pull-down when confi gured as an input, then it is unnecessary to drive ENB low to restore tri-level operation; simply confi 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 confi gura- tion is used, its pull-up current will fl ow from the GPIO into the ENB pin while it is fl oating to mid-range. Since the GPIO is driving a 1V equivalent voltage source through a resistance (looking into ENB), this current is small − possi- bly 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 imped- ance (CMOS) configuration or a weak pull-down when configured as an input. When pulled below the float voltage, the ENB pin output current is sourced from VAD or VUSB, not from the battery. Monitor State If the ENB pin is fl oating, the charger output and STATB pin will turn off 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 CV - VReQ) 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 SC820 can be forced from the monitor state (no float-charging) directly to float- 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 SC820 turns off 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 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 source is connected and the voltage on either input is between its selection and OVP limits. 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 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 neither charging input is selected and valid to charge. If the battery is already fully charged when a charge cycle is initiated, STATB is asserted for approximately 750μs before being released. The STATB pin is not asserted for automatic 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 SC820 diff 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 simul- taneous feedback signals — output voltage and output current — to the closed-loop controller. When the output voltage is suffi ciently below the CV regulation voltage, the influence of the voltage feedback is negligible and the

Applications Information (continued) 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 infl uence 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 controller is entirely in CV regulation. The soft transition eff ectively reduces the charge current below that which is permitted for a portion of the charge cycle, which increases charge time. In the SC820, 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 diff 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 programmed 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- fi 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 SC820. The thermal limiting controller reduces the output current by i T ≈ 50mA/ºC for any junction temperature TJ > TTL. When thermal limiting is inactive, TJ = TA + VΔ IFQ θJA, where VΔ is the voltage difference between the VIN pin and the BAT pin. However, if TJ computed this way exceeds TTL, then thermal limiting will become active and the thermal limiting regulation junction temperature will be TJTL = TA + VΔ I(TJTL) θJA, where I(TJTL) = IFQ − iT (TJTL − TTL). Combining these two equations and solving for T JTL, the steady state junction temperature during active thermal limiting is JAT JATLTx_FQA JTL iV1 TiIVTT T T 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 is 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 SC820 VAD input supports adapter-current-limited charging with a low deselection 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 IFQ_AD exceeds the current limit of the charging adapter IAD-LIM. Note that if IAD-LIM is less than 20% of IFQ_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

Applications Information (continued) 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 deselection falling threshold (VT ADsel-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 SC820 should be operated with adapter voltage below the rising selection threshold (VT ADSel-R ) only if the low input voltage is the result of adapter current limiting. This implies that the VAD voltage fi rst exceeds VTADsel-R to begin charging, and is subsequently 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 input fast-charge current be programmed greater than the maximum adapter current, (I AD-LIM). In this confi guration, the CC regulator will operate with its pass device fully on (in saturation, also called “dropout”). The voltage drop from VAD 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 SC820 is PILIM = (minimum R DS-ON) x (I AD-LIM)2. 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 SC820 junction temperature will rise above ambient by P ILIM x θJA. 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 TL. This implies that θJA must be kept small enough to ensure that TJ = TA + (PILIM × θJA) < TTL. VUSB Under-Voltage Load Regulation VUSB pin UVLR prevents the battery charging current from overloading the USB Vbus network, regardless of the pro- grammed fast-charge value. When the VUSB input is selected, the SC820 monitors the input voltage (V VUSB) and reduces the charge current as necessary to keep VVUSB at or above the UVLR limit (V VUSB_UV_LIM ). UVLR operates like a fourth output constraint (along with CC, CV, and CT con- straints), but it is active only when the VUSB input is selected. If the VUSB voltage is externally pulled below V USB_UV_LIM while the VAD input is absent, the UVLR feature will reduce the charging current to zero. This condition will not be interpreted as termination and will not result in an end-of- charge indication. The STATB pin will remain asserted as if charging is continuing. This prevents repetitive indica- tions of end-of-charge alternating with start-of-charge in the case that the external VUSB load is removed or is intermittent. Short Circuit Protection The SC820 can tolerate a BAT pin short circuit to ground indefi nitely. The current into a ground short is approxi- mately 10mA. 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 SC820 into reset, turning off the output. A pin-short on either programming pin will prevent startup regardless of the charging input 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 pre-charge or the fast-charge current (as

ment. In this experiment, the final steady-state BAT current was 462mA at T A = 25C on the SC820 evaluation board. The fast thermal limiting feature ensures compli- ance 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. Operation Without a Battery The SC820 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 2.2μF 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 1μF to 22μF. The VAD pin and VUSB input capacitors are typically between 0.1μF and 2.2μF, 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 — USB Charging The USB specifi cation restricts the load on the USB Vbus power network to 100mA for low power devices and for programmed by IPRGM or IPUSB, determined by input selection), depending on the voltage at the output. Input Over-Voltage Protection The VAD and VUSB input pins are protected from over- voltage to at least 30V above GND. When the voltage of the selected input 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 resumes. Note that the VAD input remains selected even in the case that the VAD voltage exceeds the OVP threshold. An excessive VAD voltage will disable charging despite the presence of a valid VUSB voltage. An OVP fault turns off the STATB output. STATB is turned on again when charging restarts. The OVP threshold 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 SC820. This behavior is illustrated in Figure 4, in which V BAT = 3.0V, IFQ = 700mA, and V VAD is stepped from 0V to 8.1V. Initially, power dissipation in the SC820 is 3.6W. 1s/div VVAD (2V/div) VVAD ,VBAT=0V— IBAT (100mA/div) IBAT=0mA— VVAD=8.1V, VBAT=3.0V IBAT=700mA (Initially), PDISSIPATION=3.6W (Initially) VBAT (2V/div) Figure 4 — 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- Applications Information (continued)

2.00.079 PIN 1 INDICATOR (LASER MARK) SEATING PLANE C BA aaa C N E 2.10 2.10 1.90 1.90 .083 .083 .075 .075 D e/2 e bxN bbb C A B COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS.2. D/2 E/2 E LxN INCHES .020 BSC b .007 bbb aaa N L e D .012 DIM A MIN .000 .020 0.400.30 .004 .003 .014 .079 .016 0.08 0.10 0.35 2.00

0.50 BSC

0.05 0.60 DIMENSIONS MIN 0.00 NOM (.006) MAX .002 .024 NOM 0.50 (0.1524) CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). NOTES: A Outline Drawing — MLPD-UT8 2x2

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Phone: (805) 498-2111 Fax: (805) 498-3804 www.semtech.com Contact Information SC820 Land Pattern — MLPD-UT8 2x2 INCHES DIMENSIONS P Z X Y C G DIM MILLIMETERS FAILURE TO DO SO MAY COMPROMISE THE THERMAL AND/OR FUNCTIONAL PERFORMANCE OF THE DEVICE. SHALL BE CONNECTED TO A SYSTEM GROUND PLANE. THERMAL VIAS IN THE LAND PATTERN OF THE EXPOSED PAD3. H .067 1.70 K .031 0.80 R .006 0.15 Y R G Z P X (C) 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). H K .030 .106 (.077) .047 0.75 2.70 (1.95) 1.20 0.30 0.50.020 .012 THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. NOTES: