® RT9531 High Efficiency Switching Mode Battery Charger General Description Features The RT9531 is a PWM switch mode battery charger controller to fast charge single or multiple Li-Ion, NiMH and NiCd batteries, using constant current or constant voltage control. Maximum current can be easily adjusted by external resistor. The constant voltage output can support up to 4 Li-Ion cells with 0.5% accuracy. A third control loop limits the input current drawing from the adapter during charging. This allows simultaneous operation of the equipment and fast battery charging without over loading to the adapter. The RT9531 can charge batteries from 2.5V to 16.8V with dropout voltage as low as 0.4V. A diode is not required in series with the battery because the charger automatically enters a 10μA sleep mode when the adapter is unplugged. A logic output indicates Li-Ion full charge when current drops to 20% of the full-scale adjusted charge current. Fast Charging for Li-Ion, NiMH and NiCd Batteries Preset Battery Voltages : 4.2V, 8.4V, 12.6V and 16.8V High Efficiency : Up to 95% Precision 0.5% Charging Voltage Accuracy 5% Charging Current Accuracy Charging Current Adjusted by Resistor 0.4V Dropout Voltage Input Current Limit Maximizes Charging Rate 475kHz Switching Frequency Flag Indicates Li-Ion Charge Completion Auto Shutdown with Adapter Removal Only 10μ μA Battery Drain When Idle Available in an WQFN-16L 4x4 Package RoHS Compliant and Halogen Free Applications Marking Information 0J= : Product Code Notebook Computers Portable Instruments Chargers for Li-Ion, NiMH, NiCd and Lead Acid Rechargeable Batteries YMDNN : Date Code 0J=YM DNN Simplified Application Circuit M1 VIN CIN RS4 C1 To System Power R2 C2 RT9531 ACN R1 D2 V5V EN ISET R3 (Option) C3 (Option) R4 R5 C4 VC VHH VHH C5 (Option) Copyright © 2015 Richtek Technology Corporation. All rights reserved. June 2015 R6 C8 M2 L1 SW STATUS C9 D1 RS1 RS3 VBATT RS2 CBATT SNSH SNSL C6 GND DS9531-01 R7 BOOT TG VIN To VHH Pin C7 ACP ACDRV D3 BATT is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT9531 Ordering Information Pin Configurations (TOP VIEW) Package Type QW : WQFN-16L 4x4 (W-Type) ACDRV EN VIN V5V RT9531- Lead Plating System G : Green (Halogen Free and Pb Free) 16 15 14 13 ACN 1 12 BOOT 11 TG 10 SW 9 STATUS VC 4 Note : Richtek products are : GND 17 5 6 7 8 SNSL 3 SNSH ISET VHH ACP 2 BATT Preset Battery Voltage A : 1-Cell (4.2V) B : 2-Cell (8.4V) C : 3-Cell (12.6V) D : 4-Cell (16.8V) WQFN-16L 4x4 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Function Pin Description Pin No. Pin Name Pin Function 1 ACN Negative Terminal to Sense Input Current. A 0.1F ceramic capacitor is placed from ACN to ACP to provide differential-mode filtering to the switching noise. 2 ACP Positive Terminal to Sense Input Current. 3 ISET Charge Current Setting and System Loop Compensation Pin. Connect a resistor from this pin to ground to set the charge current. A capacitor of at least 0.1F to GND filters out the current ripple. 4 VC Control Signal of the Inner Loop of the Current Mode PWM. It provides loop compensation and soft-start. 5 VHH To Supply the Current Sense Amplifier CA for Very Low Dropout Condition. It must be connected as shown in the typical application circuit or connected to VIN, if VIN is always larger than BATT by at least 1.8V. 6 BATT Battery Voltage Sense Input. A 10F or larger X5R ceramic capacitor is recommended for filtering charge current ripple and stability purpose. 7 SNSL Negative Terminal for Sensing Charge Current. 8 SNSH Positive Terminal for Sensing Charge Current. 9 STATUS Flag to Indicate Charge Completion. It turns to logic high when the charge current drops blew 20% of the setting charge current. A 0.1F capacitor from STATUS to ground is needed to filter the sampled charge current ripple. 10 SW Switch Node. This pin switches between ground and VIN with high dv/dt rates. Care needs to be taken in the PCB layout to keep this node from coupling to other sensitive nodes. 11 TG Gate Driver Output for the External N-MOSFET. 12 BOOT Bootstrap for High Side Gate Driver. In normal operation, VBOOT VSW + 5V. 13 V5V Output of Internal 5V LDO. Connect a 1F ceramic capacitor from this pin to GND for stability. 14 VIN Input Power Supply. Connect a low ESR capacitor of 10F or higher from this pin to ground for good bypass. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS9531-01 June 2015 RT9531 Pin No. Pin Name Pin Function 15 EN Enable Control Input, Active High. It must be connected to a logic voltage or pulled up to VIN with a 100k resistor. 16 ACDRV Gate Driver Output for Input P-MOSFET GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 17 (Exposed Pad) Function Block Diagram ACDRV VIN ACN EN R1 200k 1.4V 5V 5V C3 + DRIVER 0.5µA VREF 2.5V Reference VIN Shutdown LDO + VIN BATT UVLO + C2 - 0.4V VHH V5V + ICHG - 3.8V SLOPE COMP IVA 4 STATUS Oscillator SNSH + CA - SNSL BATT R2 PWM + C1 - ICHG RFB1 IVA VREF 2.5V RFB2 ICHG VREF 2.5V + VA - EA + BOOT TG SW S R + 100mV + ACP ACN CL + Counter ISET Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9531-01 June 2015 1.3V ICL VC GND is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT9531 Operation The RT9531 is a current-mode PWM step-down switching charger controller. The battery DC charge current is adjusted by a resistor R4 at the ISET pin and the ratio of sense resistor RS2 over RS1 in the typical application circuit. Amplifier CA converts the charge current through RS1 to a much lower sampled current ICHG (ICHG = IBATT x RS1 / RS2) fed into the ISET pin. Amplifier EA compares the output of CA with 2.5V reference voltage and drives the PWM loop to force them to be equal. Note that ICHG has both AC and DC components. High DC accuracy is achieved with averaging capacitor C3 at ISET pin. ICHG is mirrored to go through R2 and generates a ramp signal that is fed to the PWM control comparator C1, forming the current mode inner loop. An internal LDO generates a 5V to power high-side FET gate driver and VHH pin. VHH pin supplies the current amplifier CA with a voltage higher than VIN for low dropout application. For batteries like lithium that require both constant current and constant voltage charging, the 0.5% 2.5V reference and the voltage amplifier VA reduce the charge current when battery voltage reaches the normal charge voltage level. For NiMH and NiCd, VA can be used for over-voltage protection. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 CL Amplifier The amplifier CL monitors and limits the input current, normally from the AC adapter to a preset level (100mV/ RS4). At input current limit, CL will supply the adjusted current at ISET pin, thus reducing battery charging current. Charge STATUS When the charger is in voltage mode and the charge current level is reduced to 20%, the STATUS pin will turn to logic high. This charge completion signal can be used to start a timer for charge termination. A 0.1μF capacitor from STATUS to ground is needed to filter the sampled charging current ripple. ACDRV Driver The ACDRV pin drives an external P-MOSFET to avoid reverse current from battery to input supply. When input supply is removed, the RT9531 goes into a low current, 10μA maximum, sleep mode as VIN drops below the battery voltage. is a registered trademark of Richtek Technology Corporation. DS9531-01 June 2015 RT9531 Absolute Maximum Ratings (Note 1) VIN, EN, ACN, BATT, SW to GND ------------------------------------------------------------------ −0.3V to 36V ACDRV --------------------------------------------------------------------------------------------------- (ACN − 6V) to (ACN + 0.3V) ACP ------------------------------------------------------------------------------------------------------- (ACN − 0.3V) to (ACN + 0.6V) ISET, VC, STATUS, V5V to GND ------------------------------------------------------------------- −0.3V to 6V VHH ------------------------------------------------------------------------------------------------------- (BATT − 0.3V) to 40V SNSL ------------------------------------------------------------------------------------------------------ (BATT − 0.3V) to (BATT+0.3V) SNSH ----------------------------------------------------------------------------------------------------- (SNSL − 0.3V) to (SNSL+0.3V) BOOT ----------------------------------------------------------------------------------------------------- (SW − 0.3V) to (SW + 6V) TG ---------------------------------------------------------------------------------------------------------- (SW − 0.3V) to (BOOT + 0.3V) Power Dissipation, PD @ TA = 25°C WQFN-16L 4x4 ----------------------------------------------------------------------------------------- 3.5W Package Thermal Resistance (Note 2) WQFN-16L 4x4, θJA ------------------------------------------------------------------------------------ 28.5°C/W WQFN-16L 4x4, θJC ----------------------------------------------------------------------------------- 7°C/W Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------ 260°C Junction Temperature ---------------------------------------------------------------------------------- 150°C Storage Temperature Range ------------------------------------------------------------------------- −65°C to 150°C ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------- 2kV Recommended Operating Conditions (Note 4) Supply Voltage, VIN ----------------------------------------------------------------------------------- 4.5V to 28V Junction Temperature Range ------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = max (12V, VCHG + 5V), VBATT is the full charge voltage, pull-up EN to VIN with 100kΩ resistor, TA = 25°C unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit 0.5 1.3 2 mA -- -- 12 A -- -- 10 A 3.6 3.8 4.2 V -- 300 -- mV 4.179 4.2 4.221 8.358 8.4 8.442 12.537 12.6 12.663 16.716 16.8 16.884 Overall Supply Quiescent Current IQ No Charge Current Supply Shutdown Current ISD VEN = 0 Reverse Current from Battery IREV VIN Floating, Sleep Mode VIN Under-Voltage Falling Check ACDRV VUVLO_L Threshold VIN Under-Voltage Hysteresis VUVLO_HYS Charge Voltage 1-Cell Full Charge Voltage 2-Cell 3-Cell VBATT 4-Cell Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9531-01 June 2015 V is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT9531 Parameter Symbol Test Conditions Min Typ Max Unit 95 100 105 mV 0.5 -- -- mA 15 20 25 % 36 12 6 A Charge Current Measure the Voltage Drop Across RS1 Full-Scale Charge Current Sense Voltage VICHG ISET Output Current IISET Termination current Set Factor VITM SNSH Bias Current ISNSH SNSL Bias Current ISNSL No Charge Current 36 12 6 A VHH Minimum Voltage with Respect to BATT VVHH (Note 5) 1.8 2 -- V VHH Input Current IVHH No Charge Current 40 95 150 A -- 0.3 0.4 V 30 15 8 A 25 15 8 A 1/5-Scale Charge Current when STATUS from Low to High Battery Voltage VIN Minimum Voltage with ∆VIN Respect to BATT BATT Bias Current IBATT VC Pin Current IVC VV C = 0V Input Current Limit Sense Voltage VILMT Measure the Voltage Drop Across RS4 90 100 110 mV ACN Input Current IACN VACP VACN = 0.1V 8 16 34 A ACP Input Current IACP VACP VACN = 0.1V 25 50 100 A ACDRV ON Voltage VACON Measure the Voltage (VACN VACDRV ) 4 5.4 6 V ACDRV OFF Voltage VACOFF Measure the Voltage (VACN VACDRV ), VE N = 0V 0 -- 0.1 V ARDRV Pull-Down Current IACPD VACN VACDRV = 3.8V 5 10 30 A ARDRV Pull-Up Current VACN VACDRV = 0.5V, VEN = 0V 10 5 2 A 425 475 525 kHz -- 25 75 ns -- 25 75 ns 95 -- -- % -- 5 -- V Input Current Limit IACPU Switch Characteristics Switching Frequency fOSC TG Rising Time tR TG Falling Time tF VBOOT VSW = 5V, 1nF Load at TG Pin VBOOT VSW = 5V, 1nF Load at TG Pin Maximum Duty DMAX (Note 5) TG ON Voltage VTG VTG VSW Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 (Note 5) is a registered trademark of Richtek Technology Corporation. DS9531-01 June 2015 RT9531 Parameter Symbol Test Conditions Min Typ Max Unit 40mA Load at V5V, VV C = 0V 4 5.2 6 V STATUS Cap = 0.1F -- 5 -- V Regulator and Logic Characteristics LDO Output Voltage VLDO STATUS High Voltage EN Input Voltage Logic High VENH 2.5 -- -- Logic Low VENL -- -- 0.6 -- -- 10 EN Input Current IEN 0V VEN 5V V A Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. Design guarantee. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9531-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT9531 Typical Application Circuit VIN RS4 M1 SI4435 50m CIN 22µF C1 33nF R2 56 R1 100k C2 10µF x 2 To System Power 1 ACN 2 ACP 16 ACDRV 15 14 R3 Option C3 Option R4 10k RT9531 R5 10k C4 0.47µF VHH C5 Option VIN 3 ISET 4 VC 5 VHH C6 0.1µF V5V 13 BOOT EN D2 MMSD4148T1G TG C7 1µF 12 11 10 SW 9 STATUS SNSH 8 R6 10 C9 0.1µF D3 MMSD4148T1G To VHH Pin R7 10 M2 SI4412 C8 0.1µF L1 10µH D1 MBRS240LT3 RS1 50m RS3 399 VBATT RS2 399 CBATT 22µF TVS SNSL 7 BATT 6 GND 17 (Exposed Pad) Note : For application with removable battery, a TVS with appropriate rating is required as shown above. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS9531-01 June 2015 RT9531 Typical Operating Characteristics Efficiency vs. Charge Current Efficiency vs. Supply Voltage 95 95 90 90 Efficiency (%) 100 Efficiency (%) 100 4 Cell : VBATT = 16V 3 Cell : VBATT = 12V 2 Cell : VBATT = 8V 1 Cell : VBATT = 4V 85 80 75 85 4 Cell : VIN = 24V, VBATT = 16V 3 Cell : VIN = 24V VBATT = 12V 2 Cell : VIN = 24V, VBATT = 8V 1 Cell : VIN = 12V, VBATT = 4V 80 75 IBATT = 1A 70 70 0 5 10 15 20 25 30 0 1 2 5 Supply Current vs. Temperature Charge Current vs. Supply Voltage 1.3 1.20 1.16 1.2 Supply Current (mA) 1.12 1.08 1.04 1.00 0.96 1 Cell : VIN = 12V, VBATT = 4V 3 Cell : VIN = 24V VBATT = 12V 2 Cell : VIN = 24V, VBATT = 8V 4 Cell : VIN = 24V, VBATT = 16V 0.92 0.88 1.1 1.0 0.9 0.8 0.7 0.84 0.80 VIN = 12V, No Charge Current 0.6 0 5 10 15 20 25 30 -50 -25 0 Supply Voltage (V) 25 50 75 100 125 Temperature (°C) Shutdown Current vs. Temperature V5V Voltage vs. Temperature 5.20 14 12 5.16 10 V5V Voltage (V) Shutdown Current (μA) 4 Charge Current (A) Supply Voltage (V) Charge Current (A) 3 8 6 4 5.12 5.08 5.04 2 VIN = 12V, No Charge Current 0 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9531-01 June 2015 125 VIN = 12V, IV5V = 40mA 5.00 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT9531 VILIM vs. Temperature 120 4.22 115 4.21 110 4.20 105 VILIM (mV) Full Charge Voltage (V) Full Charge Voltage vs. Temperature 4.23 4.19 4.18 100 95 90 4.17 85 4.16 VIN = 12V VIN = 12V 4.15 -50 -25 0 25 50 75 100 80 -50 125 -25 0 Temperature (°C) VICHG vs. Temperature 75 100 125 ∆VIN vs. Temperature 0.16 108 0.14 106 0.12 104 102 ∆VIN (V) VICHG (mV) 50 Temperature (°C) 110 100 98 96 0.10 0.08 0.06 0.04 94 0.02 92 VBATT = 4V VIN = 12V 90 0.00 -50 -25 0 25 50 75 100 -50 125 -25 0 Temperature (°C) 25 50 75 100 125 Temperature (°C) BATT Bias Current vs. Temperature Switching Frequency vs. Supply Voltage 14 BATT Bias Current (μA) 500 Switching Frequency (kHz) 25 490 480 470 460 12 10 8 6 4 2 VIN = 12V 0 5 10 15 20 25 Supply Voltage (V) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 VIN = 12V 0 450 30 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS9531-01 June 2015 RT9531 Adapter Insert and Remove Charge Enable and Disable EN (5V/Div) VIN (10V/Div) VBATT (5V/Div) TG − SW (5V/Div) VBATT (5V/Div) TG − SW (5V/Div) IBATT (1A/Div) IBATT (1A/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (25ms/Div) Time (25ms/Div) Charge Enable Charge Disable EN (5V/Div) EN (5V/Div) VBATT (5V/Div) TG − SW (5V/Div) VBATT (5V/Div) TG − SW (5V/Div) IBATT (1A/Div) IBATT (1A/Div) VIN = 12V, VBATT = 4V, IBATT = 1A VIN = 12V, VBATT = 4V, IBATT = 1A Time (10ms/Div) Time (10ms/Div) Switching Battery to GND Short Response VBATT (5V/Div) IBATT (1A/Div) TG − SW (5V/Div) VBATT (2V/Div) IL (500mA/Div) TG − SW (5V/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (1μs/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9531-01 VIN = 12V, VBATT = 4V, IBATT = 1A June 2015 IL (1A/Div) I IN (500mA/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT9531 Application Information Input and Output Capacitors In the typical application circuit, the input capacitor (C2) is assumed to absorb all input switching ripple current in the converter, so it must have adequate ripple current rating. Typically, at high charging currents, the converter will operate in continuous conduction mode. In this case, the RMS current IRMSIN of the input capacitor C2 can be estimated by the equation : IRMSIN IBATT D D2 Where IBATT is the battery charge current and D is the duty cycle. In worst case, the RMS ripple current will be equal to one half of output charging current at 50% duty cycle. For example, IBATT = 2A, the maximum RMS current of input capacitor C2 will be 1A. Actual capacitance value is not critical. Solid tantalum capacitors such as the AVX TPS and Sprague 593D series have high ripple current rating in a relatively small surface mount package, but caution must be used when tantalum capacitors are used for input bypass. High input surge currents can be created when the adapter is hot-plugged to the charger and solid tantalum capacitors have a known failure mechanism when subjected to very high turn-on surge currents. Highest possible voltage rating on the capacitor will minimize problems. Consult the manufacturer before use. Alternatives include new high capacity ceramic (at least 20μF) from Tokin or Murata. The output capacitor (CBATT) is also assumed to absorb output switching current ripple. The general formula for capacitor current is : VBATT (1 VBATT ) VVIN IRMSCB 2 3 L1 fOSC For example, VVIN = 19V, VBATT = 8.4V, L1= 10μH, and fOSC = 475kHz, IRMS = 0.15A. EMI considerations usually make it desirable to minimize ripple current in the battery leads. Beads or inductors may be added to increase battery impedance at the 475 kHz switching frequency. Switching ripple current splits between the battery and the output capacitor depending Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 on the ESR of the output capacitor and the battery impedance. If the ESR of COUT is 0.2Ω and the battery impedance is raised to 4Ω with a bead or inductor, only 5% of the ripple current will flow in the battery. Inductor The inductor value will be changed for more or less current ripple. The higher the inductance, the lower the current ripple will be. As the physical size is kept the same, typically, higher inductance will result in higher series resistance and lower saturation current. A good tradeoff is to choose the inductor so that the current ripple is approximately 30% to 50% of the full-scale charge current. The inductor value is calculated as : V (VVIN VBATT ) L1 BATT VVIN fOSC IL Where ΔIL is the inductor current ripple. For example, VVIN = 19V, choose the inductor current ripple to be 40% of the full-scale charge current in the typical application circuit for 2A, 2-cell battery charger, ΔIL = 0.8A, VBATT = 8.4V, calculate L1 to be 12.3μH. So choose L1 to be 10μH which is close to 12.3μH. Soft-Start and Under-Voltage Lockout The soft-start is controlled by the voltage rise time at VC pin. There is external soft-start in the RT9531. With a 0.47μF capacitor, time to reach full charge current is about 25ms and it is assumed that input voltage to the charger will reach full value in less than 25ms. The capacitor can be increased if longer input start-up times are needed. For the RT9531, it provides Under-Voltage Lockout (UVLO) protection. UVLO monitoring LDO output voltage. If LDO output voltage is lower than 3.8V, high side power FET M2 and input power FET M1 will be cut off. This will protect the adapter from entering a quasi “latch” state where the adapter output stays in a current limited state at reduced output voltage. is a registered trademark of Richtek Technology Corporation. DS9531-01 June 2015 RT9531 Adapter Current Limit An important feature of RT9531 is the ability to automatically adjust charge current to a level which avoids overloading the wall adapter. This allows the product to operate, and at the same time batteries are being charged without complex load management algorithms. Additionally, batteries will automatically be charged at the maximum possible rate of which the adapter is capable. This is accomplished by sensing total adapter output current and adjusting charge current downward if a preset adapter current limit is exceeded. True analog control is used, with closed loop feedback ensuring that adapter load current remains within limits. Amplifier CL in typical application circuit senses the voltage across RS4, connected between the ACP and ACN pins. When this voltage exceeds 100mV, the amplifier will override adjusted charge current to limit adapter current to 100mV/RS4. A low pass filter formed by 56Ω and 33nF is required to eliminate switching noise. Full-Scale Charge Current Programming The basic formula for full-scale charge current is (see Block Diagram) : V IBATT = IISET RS2 = REF RS2 , VREF = 2.5V RS1 R4 RS1 Where R4 is the total resistance from ISET pin to ground. For the sense amplifier CA biasing purpose, RS3 should have the same value as RS2. For example, 2A full-scale charging current is needed. For low power dissipation on RS1 and enough signal to drive the amplifier CA, let RS1 = 100mV / 2A = 50mΩ. This limits RS1 power to 0.2W. Let R4 = 10k, then : I R 4 RS1 2A 10k 0.05 RS2 RS3 BATT 400 VREF 2.5V Note that for charge current accuracy and noise immunity, 100mV full scale level across the sense resistor RS1 is required. Consequently, both RS2 and RS3 should be 400Ω. Select 399Ω for real application. It is critical to have a good Kelvin connection on the current sense resistor RS1 to minimize stray resistive and inductive pickup. RS1 should have low parasitic inductance (typical 3nH or less, as exhibited by Dale or IRC sense resistors). The layout path from RS2 and RS3 to RS1 should be kept away from the fast switching SW node. A Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9531-01 June 2015 10pF ceramic capacitor can be used across RS1 to filter out the switching spark noise. Lithium-Ion Charging The 2A Lithium Battery Charger (typical application circuit) charges lithium-ion batteries at a constant 2A until battery voltage reaches the preset value. The charger will then automatically go into a constant voltage mode with current decreasing to near zero over time as the battery reaches full charge. The RT9531 provides four preset full charge battery voltages : 4.2V, 8.4V, 12.6V and 16.8V. See ordering information for more details. Lithium-Ion Charging Completion Some battery manufacturers recommend termination of constant voltage float mode after charge current has dropped below a specified level (typically around 20% of the full-scale charge current) and a further time-out period of 30 minutes to 90 minutes has elapsed. Check with manufacturers for details. The RT9531 provides a signal at the STATUS pin when charging is in voltage mode and charge current is reduced to 20% of full-scale charge current, assuming full-scale charge current is programmed to have 100mV across the current sense resistor (VRS1). The charge current sample ICHG (see block diagram) is compared with the output current IVA of voltage amplifier VA. When the charge current drops to 20% of full-scale charge current, ICHG will be equal to 20% of IVA and the STATUS pin voltage will go logic high and can be used to start an external timer. When this feature is used, a capacitor of at least 0.1μF is required at the STATUS pin to filter out the switching noise. If this feature is not used, the capacitor is not needed. Very Low Dropout Operation The RT9531 can charge the battery even when VIN goes as low as 0.4V above the combined voltages of the battery and the drops on the sense resistor as well as parasitic wiring. This low VIN sometimes forces 100% duty cycle and TG stays on for many switching cycles. While TG stays on, the voltage VBOOT across the capacitor C8 drops down slowly because the current sink at BOOT pin. C8 needs to be recharged before VBOOT drops too low to keep the high-side switch on. A unique design allows the RT9531 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT9531 It is important to use 0.1μF or greater value for C8 to hold VBOOT up for a sufficient amount of time. When minimum operating VIN is less than 1.8V above the battery voltage, D3 and C6 (see typical application circuit) are also needed to bootstrap VHH higher than VIN to bias the current amplifier CA. They are not needed if VIN is always at least 1.8V higher than VBATT, but VHH must be connected to VIN and do not keep VHH pin floating. The P-MOSFET M1 is optional and can be replaced with a diode if VIN is at least 2.5V higher than VBATT. The gate control pin ACDRV turns on M1 when V5V gets up above the under-voltage lockout level and is clamped internally to 5V below VACN. In sleep mode when VIN is removed, ACDRV will clamp M1 VSG to less than 0.1V. Shutdown When adapter power is removed, VIN will drift down. As soon as VIN goes down to 0.1V above VBATT, the RT9531 will go into sleep mode drawing only 10μA from the battery. There are two ways to stop switching: pulling the EN pin low or pulling the VC pin low. Pulling the EN pin low will shut down the whole chip. Pulling the VC pin low will only stop switching and LDO stays work. Make sure there is a pull-up resistor on the EN pin even if the EN pin is not used, otherwise internal pull-down current will keep the EN pin low to shut down mode when power turns on. Charger Crowbar Protection If the VIN connector of typical application circuit can be instantaneously shorted (crowbarred) to ground, the P-MOSFET M1 must be quickly turned off, otherwise, high reverse surge current might damage M1. An internal transient enhancement circuit is designed to quickly charge the ACDRV pin voltage to the ACN pin voltage. Note that the RT9531 will operate even when VBATT is grounded. If VBATT of typical application circuit charger gets shorted to ground very quickly (crowbarred) from a high battery voltage, slow loop response may allow charge current to build up and damage the high-side N-MOSFET Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 M2. A small diode from the EN pin to VBATT will shut down switching and protect the charger. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN-16L 4x4 package, the thermal resistance, θJA, is 28.5°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (28.5°C/W) = 3.5W for WQFN-16L 4x4 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 5 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 4.0 Maximum Power Dissipation (W) to operate under these conditions. If the SW pin voltage keeps larger than 1.3V for 32 oscillation periods, high-side power FET will be turned off and an internal FET will be turned on to pull the SW pin down. This function refreshes VBOOT voltage to a higher value. Four-Layer PCB 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 5. Derating Curve of Maximum Power Dissipation is a registered trademark of Richtek Technology Corporation. DS9531-01 June 2015 RT9531 Layout Considerations Switch rise and fall times are under 20ns for maximum efficiency. To prevent radiation, the power MOSFETs, the SW pin, the rectifier Schottky diode D1 and input bypass capacitor leads should be kept as short as possible. A ground plane should be used under the switching circuitry to prevent inter-plane coupling and to act as a thermal spreading path. Note that the rectifier Schottky diode D1 is probably the most heat dissipating device in the charging system. The voltage drop on a 2A Schottky diode can be 0.5V. With 50% duty cycle, the power dissipation can go as high as 0.5W. Expanded traces should be used for the diode leads for low thermal resistance. Another large heat dissipating device is probably the inductor. The fast switching high current ground path including the MOSFETs, D1 and input bypass capacitor C2 should be kept very short. Another smaller input bypass (1μF ceramic or larger paralleled with CIN) should be placed to the VIN pin and the GND pin as close as possible. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9531-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT9531 RS4 M1 ACDRV To System Power Input capacitor must be placed as close to the IC as possible. ACN2 ACP VIN GND C7 must be Placed as close to the IC as possible. CIN V5V 14 13 C2 ACN 1 12 ACP 2 11 TG ISET 3 10 SW VC 4 9 STATUS R4 GND 17 VHH 6 7 BATT 5 R5 C4 15 BOOT TG R6 CBATT M2 C8 VBATT L1 RS1 SW 8 RSH C9 SNSH R3 C3 16 SNSL C1 Locate the compensation components to the VC/ISET pin as close as possible Place these power components as close as possible. D2 R1 VIN R2 C7 EN C1 and R2 must Be placed as close to the IC as possible. ACDRV ACP ACN2 VIN RSL VBATTH D1 C5 D3 RSH RSL VBATTH Locate the bootstrap components to VHH pin as close as possible RS3 RS2 C6 VBATT BOOT GND Figure 6. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation. DS9531-01 June 2015 RT9531 Outline Dimension D SEE DETAIL A D2 L 1 E E2 e b 1 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A A1 1 2 A3 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.250 0.380 0.010 0.015 D 3.950 4.050 0.156 0.159 D2 2.000 2.450 0.079 0.096 E 3.950 4.050 0.156 0.159 E2 2.000 2.450 0.079 0.096 e L 0.650 0.500 0.026 0.600 0.020 0.024 W-Type 16L QFN 4x4 Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS9531-01 June 2015 www.richtek.com 17