RT9535A High Efficiency Switching Mode Battery Charger General Description Features The RT9535A 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 500kHz Switching Frequency the adapter during charging. This allows simultaneous Auto Shutdown with Adapter Removal operation of the equipment and fast battery charging Applications without over loading to the adapter. Notebook Computers Portable Instruments Chargers for Li-lon, NiMH, NiCd and Lead Acid The RT9535A can charge batteries from 2.5V to 22V with dropout voltage as low as 0.4V. The RT9535A is available in the WQFN-16L 4X4 Rechargeable Batteries package. Simplified Application Circuit D4 VIN C1 R1 R2 HSD EN VIN CIN C2 RT9535A D2 D3 To RS3 VHH V5V R7 ISET VC R3 R4 C3 C6 NTC C7 R6 RNTC SS R5 C5 R8 C4 BOOT C8 GND L1 RS1 VBATT SW VFB VFB D1 PGND VHH VHH RF2 SNSH RS3 RS2 CBATT To VFB RF1 SNSL BATT Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 April 2014 is a registered trademark of Richtek Technology Corporation www.richtek.com 1 RT9535A Marking Information Ordering Information RT9535A Package Type QW : WQFN-16L 4x4 (W-Type) 1Y=YM DNN Lead Plating System G : Green (Halogen Free and Pb Free) 1Y= : Product Code Note : YMDNN : Date Code 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 EN 1 SS 2 ISET 3 V5V VIN BOOT HSD (TOP VIEW) 16 15 14 13 12 SW 11 PGND 10 SNSH 9 SNSL GND 17 5 6 7 8 VFB VHH BATT 4 NTC VC WQFN-16L 4x4 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation DS9535A-02 April 2014 RT9535A Functional Pin Description Pin No. Pin Name Pin Function 1 EN Enable Control Input (Active High). It must be connected to a logical voltage or pulled up to VIN with a 100k resistor. 2 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. 3 ISET Charge Current Setting and System Loop Compensation Pin. Connect a resistor from this pin to ground to set the charge current. 4 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. 5 NTC Input for an external NTC thermistor for battery temperature monitoring. 6 VFB Battery Voltage Feedback. Using an external resistor divider to set battery full charge voltage. 7 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. 8 BATT Battery Voltage Sensing Input. A 10F or larger X5R ceramic capacitor is recommended for filtering charge current ripple and stability purpose. 9 SNSL Negative Terminal for Sensing Charge Current. 10 SNSH Positive Terminal for Sensing Charge Current. 11 PGND Power Ground. 12 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. 13 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. 14 BOOT Bootstrap Supply for the High-Side Power Switch Gate Driver and Control Circuitry. In normal operation, VBOOT ≈ VSW + 5V. 15 VIN Input Power Supply. Connect a low ESR capacitor of 10F or higher from this pin to ground for good bypass. 16 V5V Output of Internal 5V LDO. Connect a 1F ceramic capacitor from this pin to GND for stability. 17 (Exposed Pad) GND Exposed Pad. Connect the exposed pad to PGND. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 April 2014 is a registered trademark of Richtek Technology Corporation www.richtek.com 3 RT9535A Function Block Diagram R1 200k NTC VIN THERMISTOR REFERENCE 1.4V C3 EN 0.5uA 5V SD UVLO VIN V5V LDO + VIN VREF 2.5V C2 BATT 0.4V UVLO 3.9V ICHG VHH SLOP COMP OSCILLATOR SNSL BOOT R2 SNSH CA ICHG PWM C1 VREF 2.5V IVA VFB VREF 2.5V EA HSD S R SW VA 1.3V GND Soft-Start COUNTER ISET Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 SS VC PGND is a registered trademark of Richtek Technology Corporation DS9535A-02 April 2014 RT9535A Operation The RT9535A is a current mode PWM step-down switching charger controller. The battery DC charge current is programmed 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 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 current mode inner loop. An internal LDO generates a 5V to power high-side MOSFET gate driver. 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 © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 April 2014 is a registered trademark of Richtek Technology Corporation www.richtek.com 5 RT9535A Absolute Maximum Ratings (Note 1) VHH, BOOT to GND --------------------------------------------------------------------------- 0.3V to 36V VIN, EN, SW, HSD to GND ------------------------------------------------------------------ 0.3V to 30V ISET, VC, VFB, V5V SS, NTC to GND --------------------------------------------------- 0.3V to 6V BATT SNSH, SNSL to GND ----------------------------------------------------------------- 0.3V to 28V Power Dissipation, PD @ TA = 25C WQFN-16L 4x4 --------------------------------------------------------------------------------- 3.5W Package Thermal Resistance (Note 2) WQFN-16L 4x4, JA --------------------------------------------------------------------------- 28.5C/W WQFN-16L 4x4, JC --------------------------------------------------------------------------- 7C/W Lead Temperature (Soldering, 10 sec.) --------------------------------------------------- 260C Junction Temperature ------------------------------------------------------------------------- 150C Storage Temperature Range ---------------------------------------------------------------- 65C to 150C ESD Susceptibility HBM (Human Body Model) ------------------------------------------------------------------ 2kV MM (Machine Model) -------------------------------------------------------------------------- 200V (Note 3) 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 VIN Under-Voltage Lockout Hysteresis Reference VUVLO 3.6 3.8 4.3 V -- 300 -- mV Reference Voltage VFB 2.486 2.5 2.514 V FB Bias current IFB -- -- 0.1 A VUVLO_HYS Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 VFB = 2.5V is a registered trademark of Richtek Technology Corporation DS9535A-02 April 2014 RT9535A Parameter Charge Current Full-Scale Charge Current Sense Voltage Symbol VICHG Test Conditions Min Typ Max Unit Measure the Voltage Drop Across RS1 95 100 105 mV −1 -- -- mA ISET Output Current IISET SNSL Bias Current ISNSL No Charge Current −36 −12 −6 A SNSH Bias Current ISNSH No Charge Current −36 −12 −6 A -- -- 2 V Battery Voltage VHH Minimum Voltage with Respect to BATT VIN Minimum Voltage with Respect to BATT VHH Input Current VHH BATT Bias Current IBATT VC Pin Current IVC VDROP (Note 5) -- 0.3 0.4 V IVHH VHH = 28V VEN = 0, VBATT = VSW = VSNSH = VSNSL = 20V 40 95 150 A -- -- 10 A VVC = 0V −25 −15 −1 A Switch Characteristics Switching Frequency High-Side Switch On-Resistance High-Side Switch leakage Current fOSC 430 500 545 kHz RON -- 150 -- m IHSD VHSD = 28V, VEN = 0V -- -- 10 A BOOT Leakage Current IBOOT VBOOT = 30V, VEN = 0V (Note 5) -- 1 -- A VVC = 0V 95 -- -- % VSW = 28V, VEN = 0V -- -- 10 A 50mA Load at V5V, VVC = 0V 4 5 6 V Maximum Duty SW Leakage Current ILKGL Regulator and Logic Characteristics LDO Output Voltage EN Input Voltage VLDO Logic-High VENH 2.5 -- -- Logic-Low VENL -- -- 0.6 -- -- 10 A 1.5 3.3 6 A 73.5% VV5V 31% VV5V 0.2% Vv5v 75% VV5V 32.5% VV5V 1.7% Vv5v 76.5% VV5V 34% VV5V 3.2% Vv5v -- 2 10 A EN Input Current IEN Soft-Start Sourcing Current ISS 0V ≤ VEN ≤ 5V V Thermal Comparator and Protection NTC Threshold, Cold VCOLD NTC Threshold, Hot VHOT NTC Disable Threshold VDISNTC NTC Bias Current Thermal Shutdown Temperature Thermal Shutdown Hysteresis INTC April 2014 V V V TSD (Note 5) -- 160 -- °C TSD (Note 5) -- 30 -- °C Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 NTC Voltage Rising, 1% Hysteresis NTC Voltage Rising, 1% Hysteresis NTC Voltage Rising, 1% Hysteresis is a registered trademark of Richtek Technology Corporation www.richtek.com 7 RT9535A Note 1. Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to 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 © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation DS9535A-02 April 2014 RT9535A Typical Application Circuit D4 PMEG4020 VIN C1 10μF R2 10 R1 100k 1 15 HSD EN C3 (Optional) R4 10k R5 1k C4 3.3nF VIN V5V BOOT GND SW 6 VFB PGND 7 VHH R7 100k R6 100k C5 0.01μF VHH D2 16 NTC 5 3 ISET 4 VC 2 SS 17 (Exposed Pad) C9 (Optional) VFB C2 10μF x 2 RT9535A CIN 1μF R3 (Optional) 13 SNSH 14 12 11 10 9 SNSL 8 BATT C7 1μF RNTC D3 To RS3 VHH C6 0.1μF R8 10 C8 0.1μF D1 PMEG2030 L1 10μH RS3 402 RS1 0.1 RS2 402 VBATT CBATT 22μF RF2 390k To VFB RF1 100k VIN = 15V to 28V, 3 – cell, ICHARGE = 1A Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 April 2014 is a registered trademark of Richtek Technology Corporation www.richtek.com 9 RT9535A 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 © 2014 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 DS9535A-02 April 2014 RT9535A 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 © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 -25 Temperature (℃) Supply Voltage (V) April 2014 IBATT (500mA/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (25ms/Div) is a registered trademark of Richtek Technology Corporation www.richtek.com 11 RT9535A 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 © 2014 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 DS9535A-02 April 2014 RT9535A Application Information Input and Output Capacitors and the battery impedance. If the ESR of COUT is 0.2 In the typical application circuit, the input capacitor (C2) and the battery impedance is raised to 4 with a bead is assumed to absorb all input switching ripple current or inductor, only 5% of the ripple current will flow in the in the converter, so it must have adequate ripple battery. 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 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 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 : 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 typical of 2A charging current. 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. The output capacitor (CBATT) is also assumed to Soft-Start and Under-Voltage Lockout absorb output switching current ripple. The general The soft-start is controlled by the voltage rise time at formula for capacitor current is : SS pin. There are internal soft-start and external VBATT VBATT 1 VVIN IRMSCB = 2 3 L1 fosc soft-start in the RT9535A. With a 0.01F capacitor, For example, VVIN = 19V, VBATT = 8.4V, L1 = 10H, value in less than 20ms. The capacitor can be and f OSC = 500kHz, IRMS = 0.15A. increased if longer input start-up times are needed. EMI considerations usually make it desirable to For the RT9535A, it provides Under-Voltage Lockout minimize ripple current in the battery leads. Beads or (UVLO) protection. If 5V5LDO output voltage is lower inductors may be added to increase battery impedance than 3.5V, high-side internal power MOSFET. This will at the 500kHz switching frequency. Switching ripple protect the adapter from entering a quasi “latch” state current splits between the battery and the output where the adapter output stays in a current limited state capacitor depending on the ESR of the output capacitor at reduced output voltage. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 April 2014 time to reach full charge current is about 20ms and it is assumed that input voltage to the charger will reach full is a registered trademark of Richtek Technology Corporation www.richtek.com 13 RT9535A The basic formula for full-scale charge current is (see RF2 VBATT = 2.5 1+ RF1 Block Diagram) : where RF2 is connected from VFB to the battery and VREF IBATT = R4 RF1 is connected from VFB to GND. Full-Scale Charge Current Programming RS2 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 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 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. = 50m. This limits RS1 power to 0.2W. Let R4 = 10k, Dropout Operation then : RS2 = RS3 = IBATT R4 RS1 2A 10k 0.05 = = 400Ω VREF 2.5V The RT9535A can charge the battery even when VIN goes as low as 2V above the combined voltages of the Note that for charge current accuracy and noise battery and the drops on the sense resistor as well as immunity, 100mV full scale level across the sense parasitic wiring. This low VIN sometimes forces 100% resistor RS1 is required. Consequently, both RS2 and duty cycle and high-side power switch stays on for RS3 should be 402. The R4 should be set to between many switching cycles. While high-side power switch 5k and 15k for the best operation. stays on, the voltage VBOOT across the capacitor C8 It is critical to have a good Kelvin connection on the drops down slowly because the current sink at BOOT current sense resistor RS1 to minimize stray resistive pin. C8 needs to be recharged before VBOOT drops too and inductive pickup. RS1 should have low parasitic low to keep the topside switch on. inductance (typical 3nH or less). The layout path from A unique design allows the RT9535A to operate under RS2 and RS3 to RS1 should be kept away from the fast these conditions. If SW pin voltage keeps larger than switching SW node. A 1nF ceramic capacitor can be 1.3V for 32 oscillation periods, high-side power used across SNSH and SNSL and be kept away from MOSFET will be turned off and an internal MOSFET the fast switching SW node. will be turned on to pull SW pin down. This function Battery Voltage Regulation The RT9535A uses high-accuracy voltage bandgap refreshes VBOOT voltage to a higher value. It is important to use 0.1F to hold VBOOT up for a sufficient amount of time. and regulator for the high charging-voltage accuracy. The charge voltage is programmed via a resistor Shutdown divider from the battery to ground, with the midpoint When adapter power is removed, VIN will drift down. tied to the VFB pin. The voltage at the VFB pin is As soon as VIN goes down to 0.1V above VBATT, the regulated to 2.5V, giving the following equation for the RT9535A will go into sleep mode drawing only ~10A regulation voltage: from the battery. There are two suggest 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 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation DS9535A-02 April 2014 RT9535A chip. Pulling the VC pin low will only stop switching and 5V5LDO stays active. 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 Note that the RT9535A 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 high-side internal N-MOSFET. A small diode from the EN pin to VBATT will shut down switching and protect the charger. Temperature Qualification The controller RT9535A continuously monitors battery temperature by measuring the voltage between the NTC pin and GND. A negative temperature coefficient 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 : 1 1 VV5V RTHCOLD RTHHOT V V COLD HOT RT2 = VV5V VV5V RTHHOT -1 -RTHHOT -1 V HOT VCOLD VV5V -1 VCOLD RT1 = 1 1 + RT2 RTHCOLD thermistor (NTC) and an external voltage divider typically generate this voltage. The controller compares V5V this voltage against its internal thresholds to determine if charging is allowed. To initiate a charge cycle, the battery temperature must be within the VCOLD. If RT9535A RT1 NTC battery temperature is outside of this range, the RT2 controller suspends charge and the safety timer and RTH 103AT waits until the battery temperature is within the VCOLD TS Resistor Network to VHOT range. During the charge cycle, the battery temperature must be within the VCOLD and VDISNTC thresholds. If the battery temperature is outside of this Where RTHCOLD and RTHHOT which have defined in the spec of the 103AT NTC thermistor. range, the controller suspends charge and waits until Thermal Considerations the battery temperature is within the VCOLD to VHOT For continuous operation, do not exceed absolute range. The controller suspends charge by turning off maximum junction temperature. The maximum power the PWM charge MOSFETs. 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) / JA Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 April 2014 is a registered trademark of Richtek Technology Corporation www.richtek.com 15 RT9535A 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-16L 4x4 package, the thermal resistance, JA, is 28.5C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25C can be calculated by the following formula : PD(MAX) = (125C 25C) / (28.5C/W) = 3.5W for WQFN-16L 4x4 package The maximum power dissipation depends on the operating ambient temperature for fixed TJ(MAX) and thermal resistance, JA. The derating curve in Figure 1 allows the designer to see the effect of rising ambient Maximum Power Dissipation (W)1 temperature on the maximum power dissipation. 5.0 Four-Layer PCB 4.0 3.0 2.0 1.0 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 1. Derating Curve of Maximum Power Dissipation Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 16 is a registered trademark of Richtek Technology Corporation DS9535A-02 April 2014 RT9535A Layout Consideration dissipation can go as high as 0.5W. Expanded traces Switch rise and fall times are under 20ns for maximum should be used for the diode leads for low thermal efficiency. To prevent radiation, the SW pin, the rectifier resistance. Another large heat dissipating device is Schottky diode D1 and input bypass capacitor leads probably the inductor. The fast switching high current should be kept as short as possible. A ground plane ground path including the MOSFETs, D1 and input should be used under the switching circuitry to prevent bypass capacitor C2 should be kept very short. Another inter-plane coupling and to act as a thermal spreading smaller input bypass (1F ceramic or larger paralleled path. Note that the rectifier Schottky diode D1 is with CIN) should be placed to VIN pin and GND pin as probably the most heat dissipating device in the close as possible. charging system. The voltage drop on a 2A Schottky diode can be 0.5V. With 50% duty cycle, the power Input capacitor and C7 must be placed as close to the IC as possible. Place these power components as close to the SW pin as possible. Input Power, VIN D4 GND C7 SW C1 CIN C8 D2 R4 C4 VC R5 D1 BOOT 2 11 3 GND 17 4 5 6 8 L1 PGND 10 SNSH RS3 SNSL RS2 9 7 CBATT VBATT RS1 BATT 12 SW RSL 1 BATT ISET R3 14 13 VHH C3 SS 15 VFB C5 16 NTC VIN EN RSH VHH R1 VIN V5V D3 C2 HSD RB BOOT RSH RSL C6 Locate the compensation components to the SS/VC/ISET pin as close as possible. NTC C9 R6 R7 GND RF2 V5V BATT RF1 C9 must be placed as close to the IC as possible. Locate the compensation components to the NTC/VFB pin as close as possible. Figure 2. PCB Layout Guide Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS9535A-02 April 2014 is a registered trademark of Richtek Technology Corporation www.richtek.com 17 RT9535A Outline Dimension 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. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 18 is a registered trademark of Richtek Technology Corporation DS9535A-02 April 2014