RT9535B High Efficiency Switching Mode Battery Charger General Description Features The RT9535B is a PWM switch mode battery charger Fast Charging for Li-Ion, NiMH and NiCd Batteries controller to fast charge single or multiple Li-Ion, NiMH Adjustable Battery Voltages from 2.5V to 22V and NiCd batteries, using constant current or constant High Efficiency : Up to 95% voltage control. Maximum current can be easily Charging Current Programmed by Resistor programmed by external resistor. The constant voltage Precision 0.5% Charging Voltage Accuracy output can support up to 22V with 0.5% accuracy. Provide 5% Charging Current Accuracy A third control loop limits the input current drawing from Input Current Limit Maximizes Charging Rate the adapter during charging. This allows simultaneous 500kHz Switching Frequency operation of the equipment and fast battery charging Flag Indicates Li-Ion Charge Completion without over loading to the adapter. Auto Shutdown with Adapter Removal The RT9535B can charge batteries from 2.5V to 22V Only 10A Battery Reverse Current when Idle with dropout voltage as low as 0.4V. A logic output indicates Li-Ion full charge when current drops to 17% Applications Notebook Computers Portable Instruments Chargers for Li-lon, NiMH, NiCd and Lead Acid of the full-scale programmed charge current. The RT9535B is available in the WQFN-24L 4x4 package. Rechargeable Batteries Simplified Application Circuit RS4 M1 To System Power VIN CIN C1 R2 C2 R1 ACN RT9535B ACP ACDRV HSD D2 D3 V5V To VHH Pin R9 NTC RNTC EN C7 R10 VIN BOOT ISET VC R3 R4 C3 SS R5 C5 C4 C8 VFB VFB SGND VHH VHH L1 RS1 VBATT CBATT SW D1 RS3 PGND RS2 RF2 To VFB Pin SNSH RF1 SNSL BATT STATUS GND (Exposed Pad) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 April 2015 C9 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT9535B Ordering Information Marking Information RT9535B Package Type QW : WQFN-24L 4x4 (W-Type) (Exposed Pad-Option 1) 21=YM DNN 21= : Product Code YMDNN : Date Code Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Pin Configurations GND V5V VIN BOOT HSD HSD (TOP VIEW) 24 23 22 21 20 19 ACN ACP ACDRV EN SS ISET 1 18 2 17 3 16 GND 4 15 25 5 6 14 13 8 9 10 11 12 VC STATUS NTC NC VFB VHH 7 SW SW PGND SNSH SNSL BATT WQFN-24L 4x4 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015 RT9535B Functional Pin Description Pin No. Pin Name Pin Function 1 ACN Negative Terminal to Sense Input Current. A filter is needed to filter out the 500kHz switching noise. 2 ACP Positive Terminal to Sense Input Current. 3 ACDRV Drive Signal for the Gate of Input Power PFET. 4 EN Enable Control Input (Active High). It must be connected to a logical voltage or pulled up to VIN with a 100k resistor. 5 SS Soft-Start Control Input. SS controls the soft-start time. Connect a capacitor from SS pin to GND to set the soft-start time. 6 ISET Charge Current Setting and System Loop Compensation Pin. Connect a resistor from this pin to ground to set the charge current. 7 VC Control Signal of the Inner Loop of the Current Mode PWM. A capacitor of at least 0.1F with a serial resistor to GND filters out the current ripple. 8 STATUS Flag to Indicate Charge Completion. It turns to logical high when the charge current drops blew 17% of the setting charge current. A 0.1F capacitor from STATUS to ground is needed to filter the sampled charge current ripple. 9 NTC Input for an external NTC thermistor for battery temperature monitoring. 10 NC No Internal Connection. 11 VFB Battery Voltage Feedback. Using an external resistor divider to set battery full charge voltage. 12 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. 13 BATT Battery Voltage Sensing Input. A 10F or larger X5R ceramic capacitor is recommended for filtering charge current ripple and stability purpose. 14 SNSL Negative Terminal for Sensing Charge Current. 15 SNSH Positive Terminal for Sensing Charge Current. 16 PGND Power Ground. 17, 18 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. 19, 20 HSD Drain of Internal High-Side power N-MOSFET Switch. Connect a low ESR capacitor of 10F or higher from this pin to ground for good bypass. 21 BOOT Bootstrap Supply for the High-Side Power Switch Gate Driver and Control Circuitry. In normal operation, VBOOT ≈ VSW + 5V. 22 VIN Input Power Supply. Connect a low ESR capacitor of 10F or higher from this pin to ground for good bypass. 23 V5V Output of Internal 5V LDO. Connect a 1F ceramic capacitor from this pin to GND for stability. 24 GND Analog Ground. Layout input capacitor and V5V capacitor to this pin as close as possible. 25 (Exposed Pad) GND Exposed Pad. Connect the exposed pad to GND. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT9535B Function Block Diagram VIN ACDRV NTC ACN R1 200k 5V 1.4V C3 EN THERMISTOR DRIVER 0.5A 5V VREF 2.5V REFERENCE SD VIN UVLO V5V LDO + VIN BATT C2 0.4V UVLO GND 3.9V IVA ICHG VHH STATUS SLOP COMP ICHG 5 OSCILLATOR BOOT R2 SNSH CA SNSL ICHG PWM C1 VREF 2.5V IVA VFB VREF 2.5V EA HSD S R SW VA 1.3V 100mV ACN Soft-Start ICL + ACP CL COUNTER ISET Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 SS VC PGND is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015 RT9535B Operation The RT9535B is a current mode PWM step-down CL Amplifier switching charger controller. The battery DC charge The amplifier CL monitors and limits the input current, current is programmed by a resistor R4 at the ISET pin normally from the AC adapter, to a preset level (100mV and the ratio of sense resistor RS2 over RS1 in the / RS4). At input current limit, CL will supply the typical application circuit. Amplifier CA converts the programming current at ISET pin, thus reducing battery charge current through RS1 to a much lower sampled charging current. 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 Charge STATUS When the charger is in voltage mode and the charge current level is reduced to 17%, STATUS pin will turn to logic high. This charge completion signal can be used to start a timer for charge termination. A 0.1F with averaging filter R3 and C3 at ISET pin. ICHG is mirrored to go through R4 and generates a ramp signal that is fed to the PWM control comparator, forming the capacitor from STATUS to ground is needed to filter the sampled charging current ripple. current mode inner loop. An internal LDO generates a ACDRV Driver 5V to power topside FET gate driver. For batteries like The ACDRV pin drives an external P-MOSFET to avoid lithium that require both constant current and constant reverse current from battery to input supply. When voltage charging, the 0.5% 2.5V reference and the input supply is removed, the RT9535B goes into a low voltage amplifier VA reduce the charge current when current, 10A maximum, sleep mode as VIN drops battery voltage reaches the normal charge voltage level. below the battery voltage. For NiMH and NiCd, VA can be used for over voltage protection. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT9535B Absolute Maximum Ratings (Note 1) VHH, EN to GND ------------------------------------------------------------------------------- 0.3V to 36V VIN, SW, HSD, ACN to GND -------------------------------------------------------------- 0.3V to 30V ACDRV ------------------------------------------------------------------------------------------- (ACN 6V) to (ACN 0.3V) ACP ------------------------------------------------------------------------------------------------ (ACN 0.3V) to (ACN 0.6V) BATT to GND------------------------------------------------------------------------------------ 0.3V to 28V ISET, VC, VFB, V5V to GND ---------------------------------------------------------------- 0.3V to 6V SNSL ---------------------------------------------------------------------------------------------- (BATT 0.3V) to (BATT 0.3V) SNSH---------------------------------------------------------------------------------------------- (SNSL 0.3V) to (SNSL 0.3V) BOOT --------------------------------------------------------------------------------------------- (SW 0.3V) to (SW 6V) Power Dissipation, PD @ TA = 25C WQFN-24L 4x4 --------------------------------------------------------------------------------- 3.57W Package Thermal Resistance (Note 2) WQFN-24L 4x4, JA --------------------------------------------------------------------------- 28C/W WQFN-24L 4x4, JC --------------------------------------------------------------------------- 7C/W Lead Temperature (Soldering, 10 sec.) --------------------------------------------------- 260C Junction Temperature ------------------------------------------------------------------------- 150C Storage Temperature Range ---------------------------------------------------------------- 65C to 150C ESD Susceptibility (Note 3) HBM (Human Body Model) ------------------------------------------------------------------ 2kV MM (Machine Model) -------------------------------------------------------------------------- 200V Recommended Operating Conditions (Note 4) Supply Input Voltage -------------------------------------------------------------------------- 4.5V to 28V Battery Voltage, VBAT ------------------------------------------------------------------------ 2.5V to 22V Ambient Temperature Range---------------------------------------------------------------- 40C to 85C Junction Temperature Range --------------------------------------------------------------- 40C to 125C Electrical Characteristics (VIN = VBAT + 3V, VBAT is the full charge voltage, pull-up EN to VIN with 100k resistor, TA = 25C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit 0.5 1.3 2 mA Overall Supply Quiescent Current IQ No Charge Current Supply Shutdown Current ISD VEN = 0 -- -- 12 A Reverse Current from Battery IREV VIN Floating, VEN = 0, VBATT = VSW = VSNSH = VSNSL = 20V -- -- 10 A VIN Under-Voltage Lockout VUVLO 3.6 3.8 4.3 V VIN Under-Voltage Lockout Hysteresis VUVLO_HYS -- 300 -- mV Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015 RT9535B Parameter Symbol Test Conditions Min Typ Max Unit 2.488 2.5 2.512 V Reference Reference Voltage VFB FB Bias current IFB VFB = 2.5V -- -- 0.1 A Full-Scale Charge Current Sense Voltage VICHG R4 = 10k, RS3 = RS2 = 402, Measure the Voltage Drop Across RS1 95 100 105 mV ISET Output Current IISET 1 -- -- mA Termination Current Set Factor VITM 1/5-Scale Charge Current when STATUS from Low to High -- 18 25 % SNSL Bias Current ISNSH No Charge Current 36 12 6 A SNSH Bias Current ISNSH No Charge Current 36 12 6 A -- -- 2 V Charge Current Battery Voltage VHH Minimum Voltage with Respect to BATT VHH VIN Minimum Voltage with Respect to BATT VDROP (Note 5) -- 0.3 0.4 V VHH Input Current IVHH VIN = 28V 40 95 150 A BATT Bias Current IBATT VEN = 0, VBATT = VSW = VSNSH = VSNSL = 20V -- -- 10 A VC Pin Current IVC VVC = 0V 35 15 1 A Input Current Limit Sense Voltage VILMT Measure the Voltage Drop Across RS4 95 100 105 mV ACN Input Current IACN VACP − VACN = 0.1V 8 16 34 A ACP Input Current IACP VACP − VACN = 0.1V 25 50 80 A ACDRV ON Voltage VACON Measure the Voltage (VACN − VACDRV) 4 5.4 6 V ACDRV OFF Voltage VACOFF Measure the Voltage (VACN − VACDRV), VEN = 0V -- -- 0.1 V ARDRV Pull-Down Current IACPD VACN − VACDRV = 3.8V 5 10 30 A ARDRV Pull-Up Current IACPU VACN − VACDRV = 0.5V, VEN = 0V 10 5 2 A Input Current Limit Switch Characteristics Switching Frequency fOSC 430 500 545 kHz High-Side Switch On-Resistance RON -- 150 -- m High-Side Switch leakage Current IHSD VHSD = 30V, VEN = 0V -- -- 10 A BOOT Leakage Current IBOOT VBOOT = 30V, VEN = 0V (Note 5) -- 1 -- A VVC = 0V 95 -- -- % -- -- 10 A Maximum Duty SW Leakage Current ILKGL VSW = 28V, VEN = 0V Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 April 2015 (Note 5) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT9535B Parameter Symbol Test Conditions Min Typ Max Unit 50mA Load at V5V, VVC = 0V 4 5 6 V STATUS Cap = 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 A 1.5 3.3 7 A EN Input Current IEN Soft-Start Sourcing Current ISS 0V ≤ VEN ≤ 5V V Thermal Comparator and Protection NTC Threshold, Cold VCOLD NTC Voltage Rising, 1% Hysteresis 73.5% VV5V 75% VV5V 76.5% VV5V V NTC Threshold, Hot VHOT NTC Voltage Rising, 1% Hysteresis 31% VV5V 32.5% VV5V 34% VV5V V NTC Disable Threshold VDISNTC NTC Voltage Rising, 1% Hysteresis 0.2% VV5V 1.7% 3.2% VV5V VV5V V NTC Bias Current INTC Thermal Shutdown Temperature TSD Thermal Shutdown Hysteresis TSD -- 2 10 A (Note 5) -- 160 -- °C (Note 5) -- 30 -- °C 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. JA is measured at TA = 25C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. JC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. Guaranteed by design, not subjected to production test. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015 RT9535B Typical Application Circuit RS4 50m M1 SI 4435 VIN CIN 10μF C1 33nF R1 100k To System Power C2 10μF x 2 R2 56 1 ACN 2 HSD 19,20 ACDRV D2 23 V5V ACP 3 4 RT9535B To VHH Pin R9 100k NTC 9 R10 100k RNTC EN D3 C7 1μF 22 VIN R3 (Optional) C3 (Optional) R4 10k C10 (Optional) R5 1k C5 VFB 0.01μF C4 3.3nF VHH 21 BOOT 6 ISET 7 VC SW C8 0.1μF 17, 18 5 RS1 0.1 D1 SS 11 VFB PGND 24 SNSH 12 L1 10μH SGND RS3 402 16 RS2 402 To VFB Pin 15 RF1 100k SNSL 14 13 BATT 8 STATUS VHH VBATT CBATT 10μF RF2 390k C9 0.1μF GND (Exposed Pad) 25 Figure 1. System Power from VIN (VIN = 15V to 28V, 3 – cell, Icharge = 1A) D4 PMEG4030 VIN C2 10μF x 2 CIN 10μF R1 1 ACN 100k 2 3 4 RT9535B HSD V5V ACP ACDRV 19,20 D2 23 To VHH Pin R9 100k NTC 9 RNTC EN D3 R10 100k C7 1μF 22 VIN R3 (Optional) C3 (Optional) R4 10k C10 (Optional) R5 1k C4 3.3nF C5 VFB 0.01μF VHH BOOT 6 ISET 7 VC 5 SW 11 VFB PGND 24 SNSH 12 VHH C8 0.1μF 17, 18 L1 10μH RS3 402 16 RS2 402 RF2 390k CBATT 10μF To VFB Pin 15 RF1 100k SNSL 14 13 BATT 8 STATUS GND (Exposed Pad) 25 M1 SI 4435 RS1 0.1 D1 SS SGND 21 RS4 50m C1 33nF VBATT To System Power R2 56 ACN ACP BATT ACDRV C9 0.1μF Figure 2. System Power with VBATT (VIN = 15V to 28V, 3 – cell, if Isystem = 0.5A than IBATT = 0.5A) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT9535B Typical Operating Characteristics Efficiency vs. Charge Current 100 95 95 Efficiency (%) Efficiency (%) Efficiency vs. Supply Voltage 100 90 85 1 Cell : VBATT 2 Cell : VBATT 3 Cell : VBATT 4 Cell : VBATT 5 Cell : VBATT 80 75 = 4V = 8V = 12V = 16V = 20V 90 85 1 Cell : VIN = 12V, VBATT 2 Cell : VIN = 24V, VBATT 3 Cell : VIN = 24V, VBATT 4 Cell : VIN = 24V, VBATT 5 Cell : VIN = 24V, VBATT 80 75 IBATT = 1A 70 70 0 5 10 15 20 25 0.5 30 1 1.5 2 2.5 Charge Current (A) Supply Voltage (V) Charge Current vs. Supply Voltage Supply Current vs. Temperature 1.20 1.2 1.12 1.08 1.04 = 4V = 8V = 12V = 16V = 20V 1.0 Supply Current (mA) 1 Cell : VIN = 12V, VBATT 2 Cell : VIN = 24V, VBATT 3 Cell : VIN = 24V, VBATT 4 Cell : VIN = 24V, VBATT 5 Cell : VIN = 24V, VBATT 1.16 Charge Current (A) = 4V = 8V = 12V = 16V = 20V 1.00 0.96 0.92 0.88 0.8 0.6 0.4 VIN = 28V VIN = 12V 0.2 0.84 0.80 0.0 0 10 20 30 -50 -25 Supply Voltage (V) 0 25 50 75 100 125 Temperature (℃) Shutdown Current vs. Temperature V5V Voltage vs. Temperature 45 5.00 4.95 35 V5V Voltage (V) Shutdown Current (A) 40 30 25 20 VIN = 28V VIN = 12V 15 10 4.90 4.85 4.80 4.75 5 VIN = 12V, IV5V = 40mA 0 4.70 -50 -25 0 25 50 75 100 Temperature (℃) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 125 -50 -25 0 25 50 75 100 125 Temperature (℃) is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015 RT9535B VICHG vs. Temperature VFB Voltage vs. Temperature 110 2.55 108 106 2.53 VFB Voltage (V) VICHG (mV) 104 102 100 98 96 94 92 90 -50 -25 0 25 50 2.51 2.49 VIN = 4.5V VIN = 12V VIN = 28V 2.47 100 2.45 75 125 VIN = 4.5V VIN = 12V VIN = 28V -50 Temperature (°C) 0 25 50 75 100 125 Temperature (°C) BATT Bias Current vs.Temperature Switching Frequency vs. Supply Voltage 14 510 12 505 BATT Bias Current (A) Switching Frequency (kHz) -25 500 495 490 485 10 8 6 4 2 0 480 0 5 10 15 20 25 30 -50 Charge Enable and Disable 0 25 50 75 100 125 Adapter Insert and Remove VBATT (2V/Div) SW-GND (10V/Div) VBATT (2V/Div) SW-GND (10V/Div) EN (2V/Div) VIN (5V/Div) IBATT (500mA/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (25ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 -25 Temperature (℃) Supply Voltage (V) April 2015 IBATT (500mA/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (25ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT9535B Charge Enable Charge Disable VBATT (2V/Div) VBATT (2V/Div) SW-GND (10V/Div) SW-GND (10V/Div) EN (2V/Div) EN (2V/Div) IBATT (500mA/Div) VIN = 12V, VBATT = 4V, IBATT = 1A IBATT (500mA/Div) Time (10ms/Div) Time (10ms/Div) Switching VBATT (5V/Div) VBATT (5V/Div) IL (500mA/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (1s/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 BATT to GND Short Response IIN (1A/Div) IBATT (1A/Div) IL (500mA/Div) SW-GND (10V/Div) VIN = 12V, VBATT = 4V, IBATT = 1A SW-GND (10V/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015 RT9535B Application Information Input and Output Capacitors and the battery impedance is raised to 4 with a bead In the typical application circuit, the input capacitor (C2) or inductor, only 5% of the ripple current will flow in the is assumed to absorb all input switching ripple current battery. 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 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 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 will be 1A. A low-ESR ceramic capacitor such as X7R or X5R is preferred for the input-decoupling capacitor and should be placed to the drain of the high-side MOSFET and source of the low-side MOSFET as close as possible. The voltage rating of the capacitor must be higher than the normal input voltage level. Above 20F capacitance is suggested for ripple is approximately 30% to 50% of the full-scale charge current. The inductor value is calculated as : L1 = VBATT VVIN VBATT VVIN fOSC ΔIL Where IL 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, IL = 0.8A, VBATT = 8.4V, calculate L1 to be 12H. So choose L1 to be 10H which is close to 12H. typical of 2A charging current. Soft-Start and Under-Voltage Lockout The output capacitor (CBATT) is also assumed to The soft-start is controlled by the voltage rise time at absorb output switching current ripple. The general VC pin. There are internal soft-start and external formula for capacitor current is : soft-start in the RT9535B. With a 1F capacitor, time to IRMSCB VBATT VBATT 1 VVIN = 2 3 L1 fosc reach full charge current is about 60ms and it is assumed that input voltage to the charger will reach full value in less than 60ms. The capacitor can be For example, VVIN = 19V, VBATT = 8.4V, L1 = 10H, increased if longer input start-up times are needed. and f OSC = 475kHz, IRMS = 0.15A. For the RT9535B, it provides Under-Voltage Lockout EMI considerations usually make it desirable to (UVLO) protection. If LDO output voltage is lower than minimize ripple current in the battery leads. Beads or 3.9V, the internal top side power FET and input power inductors may be added to increase battery impedance FET M1 will be cut off. This will protect the adapter from at the 475kHz switching frequency. Switching ripple entering a quasi “latch” state where the adapter output current splits between the battery and the output stays in a current limited state at reduced output capacitor depending on the ESR of the output capacitor voltage. and the battery impedance. If the ESR of COUT is 0.2 Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT9535B Adapter Current Limiting For for 40°C to 85°C temperature range, the minimum An important feature of RT9535B is the ability to value for R4 is 6k. automatically adjust charge current to a level which The maximum value of R4 should be lower than 60k. 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 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). The layout path from RS2 and RS3 to RS1 should be kept away from the fast switching SW node. A 1nF ceramic capacitor can be used across SNSH and SNSL and be kept away from the fast switching SW node. exceeded. Amplifier CL in typical application circuit senses the voltage across RS4, connected between Battery Voltage Regulation the ACP and ACN pins. When this voltage exceeds The RT9535B uses high-accuracy voltage bandgap 100mV, the amplifier will override programmed charge and regulator for the high charging-voltage accuracy. current to limit adapter current to 100mV/RS4. A low The charge voltage is programmed via a resistor pass filter formed by 56 and 33nF is required to divider from the battery to ground, with the midpoint eliminate switching noise. tied to the VFB pin. The voltage at the VFB pin is regulated to 2.5V, giving the following equation for the Full-Scale Charge Current Programming The basic formula for full-scale charge current is (see Block Diagram) : regulation voltage : RF2 VBATT = 2.5 1 + RF1 VREF RS2 IBATT = R4 RS1 where RF2 is connected from VFB to the battery and Where R4 is the total resistance from ISET pin to RF1 is connected from VFB to GND. ground. For the sense amplifier CA biasing purpose, RS3 should have the same value as RS2 with 1% accuracy. 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 = 50m. This limits RS1 power to 0.2W. Let R4 = 10k, then : IBATT R4 RS1 2A 10k 0.05 RS2 = RS3 = = = 400Ω VREF 2.5V Charging The 2A Battery Charger (typical application circuit) charges lithium-ion batteries at a constant 2A until battery voltage reaches the setting 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. Charging Completion Note that for charge current accuracy and noise Some battery manufacturers recommend termination of immunity, 100mV full scale level across the sense constant voltage float mode after charge current has resistor RS1 is required. Consequently, both RS2 and dropped below a specified level (typically around 20% RS3 should be 399. For for 0°C to 85°C temperature of the full-scale charge current) and a further time-out range, the minimum value for R4 is 5.5k. period of 30 minutes to 90 minutes has elapsed. Check Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015 RT9535B with manufacturers for details. The RT9535B provides VACN. In sleep mode, when VIN is removed, ACDRV a signal at the STATUS pin when charging is in voltage will clamp M1 VSG to less than 0.1V. mode and charge current is reduced to 17% of full-scale charge current, assuming full-scale charge current is programmed to have 100mV across the current sense resistor (VRS1). Shutdown When adapter power is removed, VIN will drift down. As soon as VIN goes down to 0.1V above VBATT, the RT9535B will go into sleep mode drawing only ~10A The charge current sample ICHG is compared with the output current IVA of voltage amplifier VA. When the charge current drops to 17% 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 0.1F is required at the STATUS pin to filter out the switching noise. If this feature is not used, the capacitor is not needed. Dropout Operation The RT9535B can charge the battery even when VIN goes as low as 2V 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 topside switch on. A unique design allows the RT9535B to operate under these conditions. If SW pin voltage keeps larger than 1.3V for 32 oscillation periods, topside power FET will be turned off and an internal FET will be turned on to 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 Protection If the VIN connector of typical application circuit can be instantaneously shorted 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 ACDRV pin voltage to ACN pin voltage. Note that the RT9535B will operate even when VBATT is grounded. If VBATT of typical application circuit charger gets shorted to ground very quickly from a high battery voltage, slow loop response may allow charge current to build up and damage the topside N-MOSFET M2. A small diode from the EN pin to VBATT will shut down switching and protect the charger. pull SW pin down. This function refreshes VBOOT Temperature Qualification voltage to a higher value. It is important to use 0.1F to The controller RT9535B continuously monitors battery hold VBOOT up for a sufficient amount of time. The temperature by measuring the voltage between the P-MOSFET M1 is optional and can be replaced with a NTC pin and GND. A negative temperature coefficient diode if VIN is at least 2.5V higher than VBATT. The thermistor (NTC) and an external voltage divider gate control pin ACDRV turns on M1 when V5V gets up typically develop this voltage. The controller compares above the under-voltage lockout level and is clamped this voltage against its internal thresholds to determine internally to 5V below VACN. In sleep mode, when VIN if charging is allowed. To initiate a charge cycle, the is removed, ACDRV will clamped internally to 5V below battery temperature must be within the VCOLD. If Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT9535B battery temperature is outside of this range, the Thermal Considerations controller suspends charge and the safety timer and For continuous operation, do not exceed absolute waits until the battery temperature is within the VCOLD maximum junction temperature. The maximum power to VHOT range. During the charge cycle, the battery dissipation depends on the thermal resistance of the IC temperature must be within the VCOLD and VDISNTC package, PCB layout, rate of surrounding airflow, and thresholds. If the battery temperature is outside of this difference between junction and ambient temperature. range, the controller suspends charge and waits until The maximum power dissipation can be calculated by the battery temperature is within the VCOLD to VHOT the following formula : range. The controller suspends charge by turning off PD(MAX) = (TJ(MAX) TA) / JA the PWM charge FETs. where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and JA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125C. The junction to ambient thermal resistance, JA, is layout dependent. For WQFN-24L 4x4 package, the thermal resistance, JA, is 28C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power Assuming a 103AT NTC thermistor on the battery pack as shown in the below, the values of RT1 and RT2 can be determined by using the following equations: dissipation at TA = 25C can be calculated by the following formula : PD(MAX) = (125C 25C) / (28C/W) = 3.57W for WQFN-24L 4x4 package 1 1 VV5V RTHCOLD RTHHOT V V HOT COLD RT2 = VV5V VV5V RTHHOT 1 RTHCOLD 1 V V HOT COLD The maximum power dissipation depends on the operating ambient temperature for fixed TJ(MAX) and thermal resistance, JA. The derating curve in Figure 3 allows the designer to see the effect of rising ambient VV5V 1 VCOLD RT1 = 1 1 RT2 RTHCOLD temperature on the maximum power dissipation. V5V RT9535B RT1 NTC RT2 RTH 103AT TS Resistor Network Where RTHCOLD and RTHHOT which have defined in the spec of the 103AT NTC thermistor. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015 Maximum Power Dissipation (W)1 RT9535B Layout Consideration 5.0 Switch rise and fall times are under 20ns for maximum Four-Layer PCB 4.0 efficiency. To prevent radiation, the SW pin, the rectifier Schottky diode D1 and input bypass capacitor leads 3.0 should be kept as short as possible. A ground plane should be used under the switching circuitry to prevent 2.0 inter-plane coupling and to act as a thermal spreading 1.0 path. Note that the rectifier Schottky diode D1 is probably the most heat dissipating device in the 0.0 0 25 50 75 100 125 charging system. The voltage drop on a 2A Schottky Ambient Temperature (°C) diode can be 0.5V. With 50% duty cycle, the power Figure 3. Derating Curve of Maximum Power dissipation can go as high as 0.5W. Expanded traces Dissipation 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 (1F ceramic or larger paralleled with CIN) should be placed to VIN pin and GND pin as close as possible. SI Input Power, VIN ACP 2 17 SW 5 ISET 6 Locate the Compensation components to the SS/VC/ISET pin as close as possible. C4 R5 C9 GND 17 RSH 15 SNSH RS1 14 SNSL RS3 VBATTH SS 16 PGND RSH RSL 13 BATT 7 8 9 10 11 12 VFB 4 VBATT VHH R1 EN NC 3 NTC ACDRV CBATT RS2 L1 18 RSL VIN HSD D1 24 23 22 21 20 19 ACN 1 VC C3 VIN C5 R3 R4 Place these Power Components as close to the SW pin as possible. C2 BOOT GND D3 VHH C1 CIN STATUS BOOT RS4 ACN C7 C8 D2 V5V SW RB GND ACP ACDRV BATT Input capacitor and C7 must be placed as close to the IC as possible. C6 R6 NTC VBATTH RF2 GND R7 RF1 V5V C6 must be placed as close to the IC as possible. Figure 4. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9535B-02 April 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 17 RT9535B Outline Dimension Symbol D2 E2 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 0.180 0.300 0.007 0.012 D 3.950 4.050 0.156 0.159 Option 1 2.400 2.500 0.094 0.098 Option 2 2.650 2.750 0.104 0.108 E 3.950 4.050 0.156 0.159 Option 1 2.400 2.500 0.094 0.098 Option 2 2.650 2.750 0.104 0.108 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 24L 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 18 is a registered trademark of Richtek Technology Corporation. DS9535B-02 April 2015