® RT9538 High Efficiency Switching Mode Battery Charger General Description Features The RT9538 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 an external resistor. The constant voltage output can support up to 30V with 0.5% accuracy. Fast Charging for Li-ion, NiMH and NiCd Batteries Adjustable Battery Voltages from 2.5V to 25V High Efficiency : Up to 95% Charging Current Adjusted by Resistor Precision 0.5% Charging Voltage Accuracy Provide 5% Charging Current Accuracy 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 16-Lead WQFN Package RoHS Compliant and Halogen Free 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 RT9538 can charge batteries from 2.5V to 25V with dropout voltage as low as 2V. 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. Applications Marking Information Notebook Computers Portable Instruments Chargers for Li-ion, NiMH, NiCd and Lead Acid Rechargeable Batteries 1C= : Product Code YMDNN : Date Code 1C=YM DNN Simplified Application Circuit M1 VIN RS4 CIN C1 To System Power R2 C2 RT9538 ACN R1 D2 V5V C7 ACP ACDRV BOOT EN TG VIN C3 Option R4 R5 C4 VFB C5 Option VC VFB R6 C8 L1 M2 SW ISET R3 Option R7 STATUS D1 C9 RS1 VBATT CBATT RS3 RS2 RF2 SNSH GND SNSL To VFB RF1 BATT Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9538-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT9538 Ordering Information Pin Configurations V5V 14 13 1 12 BOOT ACP 2 11 TG ISET 3 10 SW VC 4 9 STATUS GND 6 7 8 SNSL SNSH Suitable for use in SnPb or Pb-free soldering processes. 5 VFB 17 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. 15 BATT 16 ACN Note : Richtek products are : VIN Lead Plating System G : Green (Halogen Free and Pb Free) EN Package Type QW : WQFN-16L 4x4 (W-Type) ACDRV (TOP VIEW) RT9538 WQFN-16L 4x4 Functional 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 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 the loop compensation and soft-start. 5 VFB Charge Voltage Analog Feedback Adjustment. Connect a resistor divider from output to VFB to GND to adjust the output voltage. The internal regulation limit is 2.5V. 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. A 0.1F ceramic capacitor is placed from SRN to SRP to provide differential-mode filtering. 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS9538-01 June 2015 RT9538 Pin No. Pin Name Pin Function 14 VIN Input Power Supply. Connect a low ESR capacitor of 10F or higher from this pin to ground for good bypass. 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. 17 GND (Exposed Pad) Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Function Block Diagram ACDRV EN R1 300k C3 + 1.3V 5V VIN 5µA 0.5µA Reference 5V Shutdown UVLO + VIN BATT VREF 2.5V + C2 - VIN 15µA SLOP COMP ICHG 2V LDO V5V + UVLO - VIN 3.8V IVA 4 STATUS R2 SNSH + CA - SNSL ICHG BOOT PWM VREF 2.5V IVA VREF 2.5V + VA - + C1 - EA + S TG R SW + VFB ICHG Oscillator 1.3V - 100mV + ACP + CL - ACN Counter ISET Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9538-01 June 2015 VC GND is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT9538 Operation The RT9538 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 filter R3 and C3 at the 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 FET 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. 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 RT9538 goes into a low current, 10μA maximum, sleep mode as VIN drops below the battery voltage. 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 the ISET pin, thus reducing battery charging current. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS9538-01 June 2015 RT9538 Absolute Maximum Ratings (Note 1) VIN, EN, ACN, BATT, SW to GND -----------------------------------------------------------------ACDRV --------------------------------------------------------------------------------------------------ACP ------------------------------------------------------------------------------------------------------ISET, VC, STATUS, VFB, V5V to GND ----------------------------------------------------------SNSL -----------------------------------------------------------------------------------------------------SNSH ----------------------------------------------------------------------------------------------------BOOT ----------------------------------------------------------------------------------------------------TG ---------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WQFN-16L 4x4 ----------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WQFN-16L 4x4, θJA -----------------------------------------------------------------------------------WQFN-16L 4x4, θJC ----------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------- Recommended Operating Conditions −0.3V to 36V (ACN − 6V) to (ACN + 0.3V) (ACN − 0.3V) to (ACN + 0.6V) −0.3V to 6V (BATT − 0.3V) to (BATT + 0.3V) (SNSL − 0.3V) to (SNSL + 0.3V) (SW − 0.3V) to (SW + 6V) (SW − 0.3V) to (BOOT + 0.3V) 3.5W 28.5°C/W 7°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Input 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 = VBATT + 3V, 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 Overall Supply Quiescent Current IQ No Charge Current Supply Shutdown Current ISD VEN = 0 -- -- 12 A Reverse Current from Battery IREV VIN Floating, Sleep Mode -- -- 10 A VIN Under-Voltage Falling Threshold VUVLO_L Check ACDRV 3.6 3.8 4.2 V VIN Under-Voltage Hysteresis VUVLO_HYS -- 300 -- mV Reference Reference Voltage VFB 2.488 2.5 2.512 V FB Leakage Current IFB -- -- 0.1 A Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9538-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT9538 Parameter Symbol Test Conditions Min Typ Max Unit 95 100 105 mV 0.5 -- -- mA 15 20 25 % 36 12 6 A 36 12 6 A -- 2 -- V 30 15 8 A 25 15 8 A Charge Current Full-Scale Charge Current Sense Voltage VICHG ISET Output Current I ISET Termination Current Set Factor VITM Measure the Voltage Drop Across RS1 1/5-Scale Charge Current when STATUS from Low to High SNSH Bias Current I SNSH SNSL Bias Current I SNSH No Charge Current VIN Minimum Voltage with Respect to BATT VIN (Note 5) BATT Bias Current IBATT VC Pin Current I VC VVC = 0V Input Current Limit Sense Voltage VILMT Measure the Voltage Drop Across RS4 90 100 110 mV ACN Input Current I ACN VACP VACN = 0.1V 8 16 34 A ACP Input Current I ACP 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), VEN = 0V 0 -- 0.1 V ACDRV Pull-Down Current I ACPD VACN VACDRV = 3.8V 5 10 30 A ACDRV Pull-Up Current I ACPU VACN VACDRV = 0.5V, VEN = 0V 10 5 2 A 425 475 525 kHz Battery Voltage Input Current Limit Switch Characteristics Switching Frequency f OSC TG Rising Time TR VBOOT VSW = 5V, 1nF Load at TG Pin -- 25 75 ns TG Falling Time TF VBOOT VSW = 5V, 1nF Load at TG Pin -- 25 75 ns (Note 5) 95 -- -- % -- 5 -- V 40mA Load at V5V, VVC = 0V 4 5.2 6 V STATUS Cap = 0.1F -- 5 -- V Maximum Duty TG ON Voltage VTG VTG VSW (Note 5) Regulator and Logic Characteristics LDO Output Voltage VLDO STATUS High Voltage EN Input Voltage EN Input Current Logic-High VENH 2.5 -- -- Logic-Low VENL -- -- 0.6 -- -- 10 I EN 0V VEN 5V Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 V A is a registered trademark of Richtek Technology Corporation. DS9538-01 June 2015 RT9538 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. DS9538-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT9538 Typical Application Circuit VIN M1 SI4435 CIN 22µF RS4 50m C1 33nF R2 56 C2 10µF x 2 1 R1 100k R3 Option C3 Option To System Power RT9538 ACN V5V 2 ACP 16 ACDRV 15 EN 14 VIN 3 ISET 4 R4 10k R5 10k C4 0.47µF VFB C5 Option VC 5 VFB BOOT TG SW STATUS SNSH SNSL 17 (Exposed Pad) D2 MMSD4148T1G GND BATT 13 C7 1µF R7 10 12 11 R6 10 C8 0.1µF M2 SI4412 10 9 C9 0.1µF L1 15µH D1 MBRS240LT3 RS1 50m RS3 399 VBATT RS2 399 CBATT 22µF RF2 390k 8 TVS To VFB 7 RF1 100k 6 Note : (1). For application with removable battery, a TVS with appropriate rating is required as shown above. (2). VIN = 15V to 30V, 3-cell , ladapter_limit = 2.5A, Icharge = 2A Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS9538-01 June 2015 RT9538 Typical Operating Characteristics Efficiency vs. Supply Voltage Efficiency vs. Charge Current 95 95 Efficiency (%) 100 Efficiency (%) 100 90 85 5 Cell : VBATT = 20V 4 Cell : VBATT = 16V 3 Cell : VBATT = 12V 2 Cell : VBATT = 8V 1 Cell : VBATT = 4V 80 75 90 85 5 4 3 2 1 80 75 Cell Cell Cell Cell Cell : VIN : VIN : VIN : VIN : VIN = 24V, VBATT = 20V = 24V, VBATT = 16V = 24V, VBATT = 12V = 24V, VBATT = 8V = 12V, VBATT = 4V IBATT = 1A 70 70 0 5 10 15 20 25 30 0 1 2 Supply Voltage (V) 4 5 Charge Current (A) Charge Current vs. Supply Voltage Supply Current vs. Temperature 1.3 1.20 1.12 1.08 1.04 Cell Cell Cell Cell Cell : VIN : VIN : VIN : VIN : VIN = 12V, VBATT = 4V = 24V, VBATT = 8V = 24V, VBATT = 12V = 24V, VBATT = 16V = 24V, VBATT = 20V 1.2 Supply Current (mA) 1 2 3 4 5 1.16 Charge Current (A) 3 1.00 0.96 0.92 1.1 1.0 0.9 0.8 0.88 0.7 0.84 0.6 0.80 0 5 10 15 20 25 -50 30 -25 0 Supply Voltage (V) Shutdown Current vs. Temperature 50 75 100 125 150 V5V Voltage vs. Temperature 14 5.20 12 10 V5V Voltage (V) Shutdown Current (µA)1 25 Temperature (°C) 8 6 4 5.15 5.10 5.05 2 5.00 0 -50 -25 0 25 50 75 100 125 Temperature (°C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9538-01 June 2015 150 -50 -25 0 25 50 75 100 125 150 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT9538 VICHG vs. Temperature VILIM vs. Temperature 110 120 108 115 106 VICHG (mV) VILIM (mV) 110 105 100 95 104 102 100 98 96 90 94 85 92 90 80 -50 -25 0 25 50 75 100 125 -50 150 -25 0 50 75 100 125 150 Temperature (°C) Temperature (°C) Switching Frequency vs. Supply Voltage VFB Voltage vs. Temperature 500 Switching Frequency (kHz)1 2.55 2.53 VFB Voltage (V) 25 2.51 2.49 2.47 490 480 470 460 450 2.45 -50 -25 0 25 50 75 100 125 0 150 5 10 15 20 25 Temperature (°C) Supply Voltage (V) BATT Bias Current vs. Temperature Charge Enable and Disable 30 BATT Bias Current (µA) 14 12 Enable (5V/Div) 10 8 VBATT (5V/Div) TG-SW (5V/Div) 6 4 IBATT (1A/Div) 2 VIN = 12V, VBATT = 4V, IBATT = 1A 0 -50 -25 0 25 50 75 100 125 150 Time (25ms/Div) Temperature (°C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS9538-01 June 2015 RT9538 Charge Enable Adapter Insert and Remove Enable (5V/Div) VIN (10V/Div) VBATT (5V/Div) VBATT (5V/Div) TG-SW (5V/Div) TG-SW (5V/Div) IBATT (1A/Div) VIN = 12V, VBATT = 4V, IBATT = 1A IBATT (1A/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (25ms/Div) Time (10ms/Div) Charge Disable Switching Enable (5V/Div) IBATT (1A/Div) VBATT (5V/Div) VBATT (5V/Div) TG-SW (5V/Div) IBATT (1A/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (10ms/Div) IL (500mA/Div) TG-SW (5V/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (1μs/Div) Battery to GND Short Response VBATT (5V/Div) TG-SW (5V/Div) IL (1A/Div) I IN (500mA/Div) VIN = 12V, VBATT = 4V, IBATT = 1A Time (10ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9538-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT9538 Applications Information Input and Output Capacitors Inductor 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 : 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 : IRMSIN = IBATT D D2 Where IBATT is the battery charge current and D is the duty cycle. In worst case, the IRMSIN ripple current will be equal to one half of output charging current at 50% duty cycle. For example, IBATT = 2A, the maximum IRMSIN 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. 22μF capacitance is suggested for typical of 2A charging current. The output capacitor (CBATT) is also assumed to absorb output switching current ripple. The general formula for capacitor current IRMSCB is : IRMSCB V VBATT 1 BATT VVIN = 2 3 L1 fOSC For example, VVIN = 19V, VBATT = 8.4V, L1= 10μH, and fOSC = 475kHz, IRMSCB = 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 475kHz switching frequency. Switching ripple current splits between the battery and the output capacitor depending 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. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 L1 = VBATT VVIN VBATT 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, ΔI L = 0.8A, VBATT = 8.4V, calculate L1 to be 12.3μH. So choose L1 to be 15μH which is close to 12.3μH. Soft-Start and Under-Voltage Lockout The soft-start is controlled by the voltage rising time at VC pin. There is external soft-start in the RT9538. 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 time is needed. For the RT9538, it provides Under-Voltage Lockout (UVLO) protection. If LDO output voltage is lower than 3.8V, highside 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. Adapter Current Limiting An important feature of RT9538 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. is a registered trademark of Richtek Technology Corporation. DS9538-01 June 2015 RT9538 This is accomplished by sensing total adapter output current and adjusting charge current downward if a preset adapter current limit is exceeded. 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 RS2 IBATT = REF ( ); VREF = VFB = 2.5V (typ.) 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 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 = 50mΩ. This limits RS1 power to 0.2W. Let R4 = 10kΩ, then : RS2 = RS3 = IBATT R4 RS1 2A 10k 0.05 = = 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). The layout path from RS2 and RS3 to RS1 should be kept away from the fast switching SW node. A 10pF ceramic capacitor can be used across SNSH and SNSL should be kept away from the fast switching SW node. Battery Voltage Regulation The RT9538 uses a high-accuracy voltage bandgap and regulator for the high charging-voltage accuracy. The charge voltage is programmed via a resistor divider from the battery to ground, with the midpoint tied to the VFB pin. The voltage at the VFB pin is regulated to 2.5V, giving the following equation for the regulation voltage : Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9538-01 June 2015 RF2 VBAT = 2.5 x 1 + RF1 where RF2 is connected from VFB pin to the battery and RF1 is connected from VFB pin to GND. 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 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 RT9538 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 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. Dropout Operation The RT9538 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 high-side switch on. is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT9538 It is important to use 0.1μF to hold VBOOT up for a sufficient amount of time. 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 RT9538 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 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 the ACDRV pin voltage to the ACN pin voltage. Note that the RT9538 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 N-MOSFET M2. A small diode from the EN pin to VBATT will shut down switching and protect the charger. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 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 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Maximum Power Dissipation (W)1 A unique design allows the RT9538 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. 4.0 Four-Layer PCB 3.2 2.4 1.6 0.8 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 1. Derating Curve of Maximum Power Dissipation is a registered trademark of Richtek Technology Corporation. DS9538-01 June 2015 RT9538 Layout Considerations 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 VIN pin and GND pin as close as possible. 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. RS4 M1 To System Power VIN Input capacitor must be placed as close to the IC as possible. ACN2 ACP ACDRV C7 must be placed as close to the IC as possible. GND CIN VIN C1 R3 C3 EN VIN V5V 16 15 14 13 Place these Power Components as close as possible. C2 ACN 1 12 BOOT ACP 2 11 TG ISET 3 10 SW VC 4 9 STATUS GND 7 8 SNSL SNSH C5 6 VFB R5 5 BATT 17 R4 C4 D2 ACDRV R2 Locate the Compensation components to VC/ISET pin as close as possible. C7 R1 ACN2 ACP C1 and R2 must be placed as close to the IC as possible. TG C8 R6 M2 CBATT VBATT L1 RS1 SW RSH C9 RSL VBATTH D1 RF1 RSL VBATTH VBATT Locate the Compensation components to VFB pin as close as possible. RS2 RS3 GND RSH RF2 Figure 2. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS9538-01 June 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT9538 Outline Dimension D SEE DETAIL A D2 L 1 E E2 e b A A1 1 1 2 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A3 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Dimensions In Inches Symbol 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. www.richtek.com 16 DS9538-01 June 2015