SC820EVB

SC820 Adapter/USB Dual Input Single-cell Li-ion Charger POWER MANAGEMENT Features Input voltage protection — 30V Adapter input automatically selected over USB Constant voltage — 4.2V, 1% regulation Charging by current and voltage regulation (CC/CV) Thermal limiting of charge current Programmable battery-dependent currents (adaptersourced fast-charge & pre-charge, termination) Programmable source-limited currents (USB-sourced fast-charge & pre-charge) Current-limited adapter support — reduces power dissipation in charger IC USB input limits charge current — prevents Vbus overload Instantaneous CC-to-CV transition for faster charging Three termination options — float-charge, automatic re-charge, or forced re-charge to keep the battery topped-off after termination without float-charging Soft-start — reduces load transients High operating voltage range — permits use of unregulated adapters Complies with CCSA YD/T 1591-2006 Space saving 2×2×0.6 (mm) MLPD package Pb free, Halogen free, and RoHS/WEEE compliant Description The SC820 is a dual input (adapter/USB) linear single-cell Li-ion battery charger in an 8 lead 2×2mm 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 floatcharging 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 dynamically limits load current to automatically 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 fastcharge and pre-charge current. Applications Mobile phones MP3 players GPS handheld receivers Typical Application Circuit SC820 VADAPTER USB Vbus 2.2 μF 2.2 μF VAD VUSB STATB GND ENB BAT IPRGM IPUSB 2.2 μF Battery Pack Device Load September 17, 2009 © 2009 Semtech Corporation 1 SC820 Pin Configuration Ordering Information Device SC820ULTRT(1)(2) SC820EVB VAD 1 TOP VIEW VUSB 2 7 BAT 8 ENB Package MLPD-UT-8 2×2 Evaluation Board Notes: (1) Available in tape and reel only. A reel contains 3,000 devices. (2) Pb free, halogen free, and RoHS/WEEE compliant. STATB 3 T 6 IPRGM GND 4 5 IPUSB MLPD-UT8; 2×2, 8 LEAD θJA = 68°C/W Marking Information 820 yw yw = Date Code 2 SC820 Absolute Maximum Ratings VAD and VUSB (V) . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to +30.0 BAT, IPRGM, IPUSB (V) . . . . . . . . . . . . . . . . . . . . . . -0.3 to +6.5 STATB, ENB (V) . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 to VBAT +0.3 VAD Input Current (A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . 5 VUSB Input Current (A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . 5 BAT, IPRGM, IPUSB Short-to-GND Duration . . . . . Continuous ESD Protection Level(1) (kV) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Recommended Operating Conditions Operating Ambient Temperature (°C) . . . . . . . . . -40 to +85 VAD Operating Voltage(2) ( V) . . . . . . . . . . . . . . . . 4.60 to 8.20 VUSB Operating Voltage(2) ( V). . . . . . . . . . . . . . . 4.70 to 8.20 Thermal Information Thermal Resistance, Junction to Ambient(3) (°C/W) . . . . . 68 Maximum Junction Temperature (°C) . . . . . . . . . . . . . . +150 Storage Temperature Range (°C) . . . . . . . . . . . . -65 to +150 Peak IR Reflow Temperature (10s to 30s) (°C) . . . . . . . +260 Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not recommended. NOTES: (1) Tested according to JEDEC standard JESD22-A114D. (2) Operating Voltage is the input voltage at which the charger is guaranteed to begin operation. These ranges, VTADsel-R Max to VOVP-F Min for the VAD input, VUVLR Max to VOVP-F Min for the VUSB input, apply to charging sources operating in voltage regulation. Charging sources operating in current limit may be pulled below these ranges by the charging load. Maximum operating voltage is the maximum Vsupply as defined in EIA/JEDEC Standard No. 78, paragraph 2.11. (3) 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. Electrical Characteristics Test Conditions: VVAD = VVUSB = 4.75V to 5.25V; CVAD = CVUSB = CBAT = 2.2μF; VBAT = 3.7V; Typ values at 25°C; Min and Max at -40°C < TA < 85°C, unless specified. Parameter VAD Select Rising Threshold VAD Deselect Falling Threshold (1) VUSB Select Rising Threshold VUSB Deselect Falling Threshold VUSB Select Hysteresis OVP Rising Threshold OVP Falling Threshold OVP Hysteresis VAD Charging Disabled Quiescent Current VAD Charging Enabled Quiescent Current VUSB Charging Disabled Quiescent Current Symbol VTADsel-R VTADsel-F VTUSBsel-R VTUSBsel-F VTUSBsel-H VTOVP-R VTOVP-F VTOVP-H IqVAD_DIS IqVAD_EN IqVUSB_DIS Conditions Min 4.30 Typ 4.45 2.85 4.20 Max 4.60 3.00 4.35 Units V V V V mV VVAD > VBAT VVUSB > VBAT VVUSB > VBAT VTUSBsel-R - V TUSBsel-F VAD or VUSB input VAD or VUSB input (VTOVP-R - V TOVP-F) VVUSB = 0V, VENB = VBAT VVUSB = 0V, VENB = 0V, excluding IBAT, IIPRGM, and IIPUSB VVAD = 0V; VENB = VBAT 2.70 3.65 100 4.00 9.6 8.2 50 2 2 2 3 3 3 V V mV mA mA mA 3 SC820 Electrical Characteristics (continued) Parameter VUSB Charging Enabled Quiescent Current VUSB Deselected Quiescent Current(2) CV Regulation Voltage Symbol IqVUSB_EN IqVUSB_DES VCV (3) Conditions VVAD = 0V, VENB = 0V, excluding IBAT, IIPRGM, and IIPUSB VVAD ≥ VVUSB IBAT = 50mA, -40°C ≤ TJ ≤ 125°C Relative to VCV @ 50mA, VVAD = 5V, or VVUSB = 5V and VVAD = 0V, 1mA ≤ IBAT ≤ 700mA, -40°C ≤ TJ ≤ 125°C Min Typ 2 25 Max 3 50 4.24 Units mA μA V 4.16 4.20 CV Voltage Load Regulation VCV_LOAD VTReQ VTPreQ lBAT_V0 -20 10 mV Re-charge Threshold Pre-charge Threshold (rising) VCV — VBAT 60 2.85 100 2.90 0.1 0.1 0.1 140 2.95 1 1 1 29.4 mV V μA μA μA kΩ mA mA mA V kΩ mA mA V V V V V V VBAT = VCV, VVAD = VVUSB = 0V VBAT = VCV, VVAD = VVUSB = 5V, VENB = 2V VBAT = VCV, VVAD = VVUSB = 5V, ENB not connected 2.05 RIPRGM = 2.94kΩ, VTPreQ < VBAT < VCV RIPRGM = 2.94kΩ, 1.8V < VBAT < V TPreQ RIPRGM = 2.94kΩ, VBAT = VCV IBAT = 700mA, 0°C ≤ TJ ≤ 125°C 4.42 RIPUSB = 4.42kΩ, VTPreQ < VBAT < VCV RIPUSB = 4.42kΩ, 1.8V < VBAT < V TPreQ IBAT = 500mA, 0°C ≤ TJ ≤ 125°C VVAD = 5.0V, VVUSB = 0V, VTPreQ < VBAT < VCV VBAT < V TPreQ VBAT = VCV (either input selected) VVAD = 0V, VTPreQ < VBAT < VCV VVAD = 0V, VBAT < V TPreQ 5mA ≤ VUSB supply current limit ≤ 500mA, VVAD = 0V, RIPUSB = 3.65kΩ (559mA) 4.40 427 69 643 105 59 Battery Leakage Current lBAT_DIS lBAT_MON IPRGM Programming Resistor Fast-Charge Current, VAD input Pre-Charge Current, VAD input Termination Current, either input VAD to BAT Dropout Voltage IPUSB Programming Resistor Fast-Charge Current, VUSB input Pre-Charge Current, VUSB input VUSB to BAT Dropout Voltage IPRGM Fast-charge Regulated Voltage IPRGM Pre-charge Regulated Voltage IPRGM Termination Threshold Voltage IPUSB Fast-charge Regulated Voltage IPUSB Pre-charge Regulated Voltage VUSB Under-Voltage Load Regulation Limiting Voltage RIPRGM IFQ_AD IPreQ_AD ITERM VDO_AD RIPUSB IFQ_USB IPreQ_USB VDO_USB VIPRGM_FQ VIPRGM_PQ VTIPRGM_TERM VIPUSB_FQ VIPUSB_PQ VUVLR 694 139 69 0.75 745 173 80 1.0 29.4 462 92 0.55 2.04 0.408 0.204 2.04 0.408 497 116 1 4.57 4.70 V 4 SC820 Electrical Characteristics (continued) Parameter Thermal Limiting Threshold Temperature Thermal Limiting Rate ENB Input High Voltage ENB Input Mid Voltage ENB Input Low Voltage ENB Input High-range Threshold Input Current ENB Input High-range Sustain Input Current ENB Input Mid-range Load Limit ENB Input Low-range Input Current ENB Input Leakage STATB Output Low Voltage STATB Output High Current Symbol T TL iT VIH VIM VIL IIH_TH Conditions Min Typ 130 Max Units °C mA/ °C V TJ > T TL 1.6 0.7 -50 1.3 0.3 V V μA ENB current required to pull ENB from floating midrange into high range Current required to hold ENB in high range, Min VIH ≤ VENB ≤ VBAT, Min VIH ≤ VBAT ≤ 4.2V Input will float to mid range when this load limit is observed. 0V ≤ VENB ≤ Max VIL VVIN = 0V, VENB = VBAT = 4.2V ISTAT_SINK = 2mA VSTAT = 5V -5 -25 23 50 IIH_SUS 0.3 1 μA IIM IIL IILEAK VSTAT_LO ISTAT_HI 5 -12 1 0.5 1 μA μA μA V μA Notes: (1) Sustained operation to VTADsel-F ≤ VVAD is guaranteed only if a current limited charging source applied to VAD is pulled below VTADsel-R by the charging load; forced VAD voltage below VTADsel-R may in some cases result in regulation errors or other unexpected behavior. (2) If VAD is the selected input but VVAD < 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. (3) 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 specification of VDO_AD. Although this is a safe and acceptable mode of operation, specification 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. 5 SC820 Typical Characteristics CV Line Regulation TA = 25 C, IBAT = 50mA 4.204 4.204 ο ο CV Load Regulation TA = 25 C, VVAD = 5V 4.2 4.2 4.196 4.196 VBAT (V) VBAT (V) 4.192 4.192 4.188 4.188 4.184 4.184 4.18 5 5.5 6 6.5 7 7.5 8 4.18 0 100 200 300 400 500 600 700 800 VVAD (V) IBAT (mA) CV Temperature Regulation VVAD = 5V, IBAT = 50mA 4.204 720 680 640 4.196 CC FQ Line Regulation (AD or USB) TA = 25 C, VBAT = 3.7V ο 4.2 RIPRGM or RIPUSB = 2.94kΩ IBAT (mA) VBAT (V) 600 560 520 4.192 4.188 RIPRGM or RIPUSB = 4.42kΩ 4.184 480 440 4.5 4.18 -40 -20 0 20 40 60 o 80 100 120 5 5.5 6 6.5 7 7.5 8 Ambient Temperature ( C) VVAD (V) CC FQ VBAT Regulation (AD or USB) TA = 25 C, VVAD = 5V 720 680 640 720 680 640 ο CC FQ Temperature Regulation (AD or USB) VVAD = 5V, VBAT = 3.7V RIPRGM or RIPUSB = 2.94kΩ IBAT (mA) 600 560 520 480 440 2.9 RIPRGM or RIPUSB = 4.42kΩ IBAT (mA) 3.1 3.3 3.5 3.7 3.9 4.1 600 560 520 480 440 -40 -20 0 20 40 60 o 80 100 120 VBAT (V) Ambient Temperature ( C) 6 SC820 Typical Characteristics (continued) CC PQ Line Regulation (AD or USB) TA = 25 C, VBAT = 2.6V 160 150 140 160 150 140 RIPRGM or RIPUSB = 2.94kΩ ο CC PQ Temperature Regulation (AD or USB) VVAD = 5V, VBAT = 2.6V RIPRGM or RIPUSB = 2.94kΩ IBAT (mA) IBAT (mA) 130 120 110 100 90 130 120 110 100 90 RIPRGM or RIPUSB = 4.42kΩ RIPRGM or RIPUSB = 4.42kΩ 5 5.5 6 6.5 7 7.5 8 -40 -20 0 20 40 60 o 80 100 120 VVAD (V) Ambient Temperature ( C) FQ_AD IPRGM ο VVAD = 5V, VBAT = 3.7V, TA = 25 C 1000 I vs. R , or IFQ_USB vs. RIPUSB 200 PQ_AD IPRGM ο VVAD = 5V, VBAT = 2.6V, TA = 25 C I vs. R , or IPQ_USB vs. RIPUSB 800 160 IBAT (mA) IBAT (mA) 6 10 14 18 22 26 30 600 120 400 80 200 40 0 2 RIPRGM or RIPUSB (kΩ ) 0 2 6 10 RIPRGM or RIPUSB (kΩ ) 14 18 22 26 30 CC — Input Reselection, AD to USB VBAT=3.7V, VVUSB=5.0V CC — Input Reselection, USB to AD VBAT=3.7V, VVUSB=5.0V VVAD (1.0V/div) VVAD (1.0V/div) IBAT (200mA/div) IBAT (200mA/div) VVAD=0V— IBAT=0mA— 400μs/div VVAD=0V— IBAT=0mA— 400μs/div 7 SC820 Typical Characteristics (continued) Charging Cycle Battery Voltage and Current 850mAhr battery, RIPRGM = 2.94kΩ , VVAD = 5.0V, TA = 25 C 4 7 6 5 700 3.75 600 3.5 500 3.25 IBAT 600 500 400 VBAT 2.75 2.5 2.25 2 0 300 200 100 0 20 700 ο Pre-Charging Battery Voltage and Current 850mAhr battery, RIPRGM = 2.94kΩ , VVAD = 5.0V, TA = 25 C 800 ο IBAT (mA) 4 3 2 1 0 0 IBAT 400 300 200 100 0 2.25 3 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2 4 6 8 10 12 14 16 18 Time (hrs) Time (s) CC-to-CV Battery Voltage and Current 850mAhr battery, RIPRGM = 2.94kΩ , VVAD = 5.0V, TA = 25 C 4.21 710 4.5 4 690 3.5 3 ο Re-Charge Cycle Battery Voltage and Current 850mAhr battery, RIPRGM = 2.94kΩ , VVAD = 5.0V, Load = 10mA 450 VBAT 400 350 300 250 200 150 IBAT 100 50 Discharge hours 2 - 6 omitted. 0 7.5 4.2 IBAT IBAT (mA) 2.5 2 1.5 4.18 VBAT 4.17 650 630 1 0.5 4.16 44 44.5 45 45.5 46 46.5 47 47.5 610 48 0 0.0 0.5 1.0 1.5 2/6 6.5 7.0 Time (min) Time (hrs) 8 IBAT (mA) VBAT (V) VBAT (V) 4.19 670 IBAT (mA) VBAT (V) VBAT (V) VBAT SC820 Pin Descriptions Pin # 1 2 Pin Name VAD VUSB Pin Function Supply pin — connect to charging adapter. This pin is protected against damage due to high voltage up to 30V. 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. 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. Ground 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. 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 threshold current (for either VAD or VUSB input selection) is 10% of the IPRGM programmed fast-charge current. Charger output 3 STATB 4 GND 5 IPUSB 6 IPRGM 7 BAT — connect to battery positive terminal. 8 ENB Combined device enable/disable — Logic high disables the device. Tie to GND to enable charging with indefinite float-charging. Float this pin to enable charging without float-charge upon termination. Note that this pin must be grounded if the SC820 is to be operated without a battery connected to BAT. Pad is for heatsinking purposes — not connected internally. Connect exposed pad to ground plane using multiple vias. T Thermal Pad 9 SC820 Block Diagram V_Adapter USB_VBUS 1 VAD 2 VUSB Input Selection Logic Ad/USB select Regulated System Supply VVUSB_UV_LIM = 4.57V Connect to BAT or to regulated supply VCV = 4.2V CV BAT To System Load 7 VIREF CC LithiumIon Single Cell Battery Pack Die Temperature VT_CT Thermal Limiting CC Feedback Selection 3 STATB Pre-charge, CC/ CV & Termination Controller, Logical State Machine Termination VTIPRGM_TERM VTENB_HIGH = ~1.50V 1V Tri-level Control VTENB_LOW = ~0.55 ENB IPUSB IPRGM GND 8 RIPUSB 5 RIPRGM 6 4 10 SC820 Applications Information Charger Operation 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 programmed 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 specification, are programmed using the IPUSB pin. When a valid input supply is first 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 threshold, 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 programmed fast-charge current) to reduce adapter load transients. CC current is programmed by the IPRGM resistance 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 singlecell Li-ion regulation voltage (VCV ), 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 IBAT drops below the termination threshold current, which is 10% of the IPRGM pin programmed fast-charge current regardless of the input selected. This is known as charge termination. (VTReQ = 100mV typically). A re-charge cycle then begins automatically and the process repeats. A forced re-charge cycle can also be periodically commanded by the processor to keep the battery topped-off without float-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 differ in selection rising and de-selection falling thresholds, 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 filtering is performed on the VAD and VUSB inputs, so an applied input voltage that is ringing across its selection 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 (defined 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 (approximately 1ms) interruption in output current and a release and re-assertion of the STATB pin during input res-election. 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. This is referred to as Current-Limited-Adapter (CLA) operation. The adapter input de-selection falling threshold is set close to the battery voltage pre-charge threshold to permit low-dissipation charging from a current limited adapter. 11 Optional Float-charging or Monitoring Depending on the state of the ENB input, upon termination the SC820 either operates indefinitely as a voltage regulator (float-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 SC820 Applications Information (continued) The VUSB input provides a higher de-selection falling threshold appropriate to the USB specification. The USB input also provides Under-Voltage Load Regulation (UVLR), in which the charging current is reduced if needed to prevent overloading of the USB Vbus supply. UVLR can serve as a low-cost alternative to directly programming the USB low power charge current (by switching the IPUSB resistor), or where there is no signal available to indicate whether USB low or high power mode should be selected. Constant Current Mode Fast-charge Current Programming The Constant Current (CC) mode is active when the battery voltage is above the pre-charge threshold voltage (VTPreQ) and less than VCV. When VAD is the selected input, the programmed CC regulation fast-charge (FQ) current is inversely proportional to the IPRGM pin resistance to GND according to the equation The nominal fast-charge current for either input can be programmed to the minimum of 70mA (RIPxxx = 29.4kΩ). The maximum fast-charge current for the VAD input is 995mA nominally (RIPRGM = 2.05kΩ), and for the VUSB input, the programmed fast-charge current should not exceed 450mA (RIPUSB = 4.42kΩ) nominally. (If a greater USB input fast-charge current is desired, please contact your Semtech Field Applications Engineer for assistance.) The VAD input is designed for lower dropout voltage at high current, which ensures charging without thermal limiting with a charging adapter operating in current limit of at least 700mA. Current regulation accuracy is dominated by gain error at high current settings and offset error at low current settings. The range of expected fast-charge output current versus programming resistance RIPRGM or RIPUSB (for VAD or VUSB input selected, respectively) is shown in Figures 1a and 1b. The figures show the nominal current versus nominal RIPRGM or RIPUSB resistance as the center plot and two theoretical limit plots indicating maximum and minimum current versus nominal programming resistance. These plots are derived from models of the expected worst-case contribution of error sources depending on programmed current. The current range 325 300 275 250 When VUSB is the selected input, the programmed CC mode fast-charge current is inversely proportional to the IPUSB pin resistance to GND according to the equation 1100 1050 1000 950 900 Fast-charge Current (mA) 800 750 700 650 600 550 500 450 400 350 Fast-charge Current (mA) 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 850 225 200 175 150 125 100 75 300 250 2 50 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 RIPRGM or RIPUSB (kΩ ), R-tol = 1% RIPRGM or RIPUSB (kΩ ), R-tol = 1% Figure 1a — Fast-charge Current Tolerance versus Programming Resistance, Low Resistance Range Figure 1b — Fast-charge Current Tolerance versus Programming Resistance, High Resistance Range 12 SC820 Applications Information (continued) includes the uncertainty due to 1% tolerance resistors. The dots on each plot indicate the currents obtained with the Electronic Industries Association (EIA) E96 standard value 1% tolerance resistors. Figures 1a and 1b show low and high resistance ranges, respectively. value 1% tolerance resistors. Figures 2a and 2b show low and high resistance ranges, respectively. Termination When the battery voltage reaches VCV, the SC820 transitions from constant current regulation to constant voltage regulation. While VBAT is regulated to VCV, the current into the battery decreases as the battery becomes fully charged. When the output current drops below the termination threshold current, charging terminates. Upon termination, the STATB pin open drain output turns off and the charger either enters monitor state or floatcharges the battery, depending on the logical state of the ENB input pin. The termination threshold current is fixed at 10% of the VAD input fast-charge current, as programmed by the resistance between IPRGM and GND. The IPRGM pin resistance determines the termination threshold current regardless of whether the selected charging input is VAD or VUSB. Charger output current is the sum of the battery charge current and the system load current. Battery charge current changes gradually, and establishes a slowly diminishing lower bound on the output current while charging in CV mode. The load current into a typical digital system is highly transient in nature. Charge cycle termination is detected when the sum of the battery charging current and the greatest load current occurring 80 75 70 65 60 Pre-charge Mode This mode is automatically enabled when the battery voltage is below the pre-charge threshold voltage (VTPreQ), typically 2.9V. Pre-charge current conditions the battery for fast charging. The pre-charge current value is fixed at 20% nominally of the fast-charge current for the selected input. The fast-charge current is programmed by the resistance between IPRGM and GND for the VAD input, and by the resistance between IPUSB and GND for the VUSB input. Pre-charge current regulation accuracy is dominated by offset error. The range of expected pre-charge output current versus programming resistance is shown in Figures 2a and 2b. The figures show the nominal pre-charge current versus nominal resistance as the center plot and two theoretical limit plots indicating maximum and minimum current versus nominal programming resistance. These plots are derived from models of the expected worst-case contribution of error sources depending on programmed current. The current range includes the uncertainty due to 1% tolerance resistors. The dots on each plot indicate the currents obtained with the Electronic Industries Association (EIA) E96 standard 270 260 250 240 230 220 210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 Pre-charge Current (mA) Pre-charge Current (mA) 55 50 45 40 35 30 25 20 15 10 5 0 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 RIPRGM or RIPUSB (kΩ ), R-tol = 1% RIPRGM or RIPUSB (kΩ ), R-tol = 1% Figure 2a — Pre-charge Current Tolerance versus Programming Resistance, Low Resistance Range Figure 2b — Pre-charge Current Tolerance versus Programming Resistance, High Resistance Range 13 SC820 Applications Information (continued) 115 110 105 100 30 35 Termination Current Threshold (mA) 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 2 Termination Current Threshold (mA) 95 25 20 15 10 5 0 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 RIPRGM (kΩ ), R-tol = 1% RIPRGM (kΩ ), R-tol = 1% Figure 3a — Termination Current Tolerance versus Programming Resistance, Low Resistance Range within the immediate 300μs to 550μs past interval is less than the programmed termination current. This timing behavior permits charge cycle termination to occur during a brief low-load-current interval, and does not require that the longer interval average load current be small. Termination threshold current accuracy is dominated by offset error. The range of expected termination current versus programming resistance RIPRGM (for either VAD or VUSB input selected) is shown in Figures 3a and 3b. The figures show the nominal termination current versus nominal RIPRGM resistance as the center plot and two theoretical limit plots indicating maximum and minimum current versus nominal programming resistance. These plots are derived from models of the expected worst-case contribution of error sources depending on programmed current. The current range includes the uncertainty due to a 1% tolerance resistor. The dots on each plot indicate the currents obtained with the Electronic Industries Association (EIA) E96 standard value 1% tolerance resistors. Figures 3a and 3b show low and high resistance ranges, respectively. Figure 3b — Termination Current Tolerance versus Programming Resistance, High Resistance Range • • Charging enabled with float-charging disabled and battery monitoring at termination (ENB = mid range) Charging disabled (ENB = high range). This input is designed to interface to a processor GPIO port powered from a peripheral supply voltage as low as 1.8V or as high as a fully charged battery. While a connected GPIO port is configured as an output, the processor writes a 0 to select ENB low-range, and 1 to select high-range. The GPIO port is configured as an input to select mid-range. ENB can also be permanently grounded to select lowrange or left unconnected to select mid-range if it will not be necessary to change the level selection. The equivalent circuit looking into the ENB pin is a variable resistance, minimum 15kΩ, to an approximately 1V source. The input will float to mid range whenever the external driver sinks or sources less than 5μA, a common worst-case characteristic of a high impedance or a weak pull-up or pull-down GPIO configured as an input. The driving GPIO must be able to sink at least 25μA or source at least 50μA to ensure a low or high state, respectively. (See the Electrical Characteristics table.) With the ENB input voltage floating to mid-range, the charger is enabled but it will turn off its output following charge termination and will enter the monitor state. This 14 Enable Input The ENB pin is a tri-level logical input that allows selection of the following behaviors: • Charging enabled with float-charging after termination (ENB = low range) SC820 Applications Information (continued) state is explained in the next section. Mid-range can be selected either by floating the input (sourcing or sinking less than 5μA) or by being externally forced such that VENB falls within the midrange limits specified in the Electrical Characteristics table. While driven low (VENB < Max VIL), the charger is enabled and will continue to float-charge the battery following termination. If the charger is already in monitor state following a previous termination, it will exit the monitor state and begin float-charging. While ENB is driven high (VENB > Min VIH), the charger is disabled and the ENB input pin enters a high impedance state, suspending tri-level functionality. The specified high level input current IIH is required only until a high level is recognized by the SC820 internal logic. The trilevel float circuitry is then disabled and the ENB input becomes high impedance. Once forced high, the ENB pin will not float to mid range. To restore tri-level operation, the ENB pin must first be pulled down to mid or low range (at least to VENB < Max VIM), then, if desired, released (by reconfiguring the GPIO as an input) to select mid-range. If the ENB GPIO has a weak pull-down when configured as an input, then it is unnecessary to drive ENB low to restore tri-level operation; simply configure the GPIO as an input. When the ENB selection changes from high-range to midor low-range, a new charge cycle begins and STATB goes low. Note that if a GPIO with a weak pull-up input configuration is used, its pull-up current will flow from the GPIO into the ENB pin while it is floating to mid-range. Since the GPIO is driving a 1V equivalent voltage source through a resistance (looking into ENB), this current is small − possibly 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 configured as an input. When pulled below the float voltage, the ENB pin output current is sourced from VAD or VUSB (the charging source), not from the battery. Monitor State If the ENB pin is floating, 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 (VCV - VReQ) while in the monitor state, the charger will automatically initiate a recharge 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 floatcharging 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 midrange, 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 millisecond. 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 automatic 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 end15 SC820 Applications Information (continued) 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. The logical transition from CC to CV results in the fastest possible charging cycle that is compliant with the specified 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 iT ≈ –50mA/ºC for any junction temperature TJ > T TL. 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 T TL, 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 − T TL). (Note that iT is a negative quantity.) Combining these two equations and solving for TJTL, the steady state junction temperature during active thermal limiting is TJTL TA V IFQ _ x iT TTL 1 V iT JA JA Logical CC-to-CV Transition The SC820 differs 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 influence 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 influence 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 effectively 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 difference between the transition voltage and the regulation 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 fastcharge current, the controller reverts to current regulation. 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(TJTL), reducing power dissipation such that die temperature equilibrium TJTL i s reached. 16 SC820 Applications Information (continued) While thermal limiting is active, all charger functions remain active and the charger logical state is preserved. current, (IAD-LIM). In this configuration, 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 RDS-ON of the pass device multiplied by the adapter supply current. In dropout, the power dissipation in the SC820 is PILIM = (minimum RDS-ON) x (IAD-LIM)2. Since minimum RDS-ON does not vary with battery voltage, dropout power dissipation 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 PILIM x θJA. If the device temperature rises to the temperature at which the TL 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 TL regulation will further limit charge current. This will keep the adapter in voltage regulation for the remainder of the charge cycle. In this case, the SC820 will continue to charge with thermal limiting until charge current decreases while in CV regulation (reducing power dissipation sufficiently), resulting in a slow charge cycle, but with no other negative effect. To ensure that the adapter remains in current limit, the internal device temperature must not rise to T TL. This implies that θJA must be kept small enough, through careful layout, to ensure that TJ = TA + (PILIM × θJA) < T TL. Operating a Charging Adapter in Current Limit In high charging current applications, charger power dissipation can be greatly reduced by operating the charging adapter in current limit. The SC820 VAD input supports adapter-current-limited charging with a low de-selection falling threshold and with internal circuitry designed for low input voltage operation. To operate an adapter in current limit, RIPRGM 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 IFQ_AD at least until the battery voltage exceeds the pre-charge threshold. 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 internal reference voltage to below the battery voltage. This will prematurely advance the charger logic from precharge current regulation to fast-charge regulation, and the charge current will exceed the safe level recommended for pre-charge conditioning. The low de-selection falling threshold (VTADsel-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 fastcharge current. The SC820 should be operated with adapter voltage below the rising selection threshold (VTADSel-R) only if the low input voltage is the result of adapter current limiting. This implies that the VAD voltage first 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 VUSB Under-Voltage Load Regulation VUSB pin UVLR prevents the battery charging current from overloading the USB Vbus network, regardless of the programmed fast-charge value. When the VUSB input is selected, the SC820 monitors the input voltage (VVUSB) and reduces the charge current as necessary to keep VVUSB at or above the UVLR limit of VUVLR = 4.57V typically. UVLR operates like a fourth output constraint (along with CC, CV, and CT constraints), but it is active only when the VUSB input is selected. If the VUSB voltage is externally pulled below VUVLR 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-ofcharge indication. The STATB pin will remain asserted as if charging is continuing. This prevents repetitive indica17 SC820 Applications Information (continued) tions of end-of-charge alternating with start-of-charge in the case that the external VUSB load is removed or is intermittent. conduction of heat from the die to the ambient environment. In this experiment, the final steady-state BAT current was 462mA at TA = 25C on the SC820 evaluation board. 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. Input Over-Voltage Protection The VAD and VUSB input pins are protected from overvoltage to at least 30V above GND. When the voltage of the selected input exceeds the Over-Voltage Protection (OVP) rising threshold (VTOVP-R), charging is halted. When the input voltage falls below the OVP falling threshold (VTOVP-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 VBAT = 3.0V, IFQ = 700mA, and VVAD is stepped from 0V to 8.1V. Initially, power dissipation in the SC820 is 3.6W. VVAD=8.1V, VBAT=3.0V IBAT=700mA (Initially), PDISSIPATION=3.6W (Initially) IBAT (100mA/div) Short Circuit Protection The SC820 can tolerate a BAT pin short circuit to ground indefinitely. The current into a ground short (while VBAT < 1.8V) is approximately 10mA. For VBAT > 1.8V, normal pre-charge current regulation is active. A short circuit or too little programming resistance to ground on the IPRGM pin (