19-6038; Rev 0; 9/11 TION KIT EVALUA BLE IL AVA A Step-Up Converter for Handheld Applications The MAX8969 is a simple 1A step-up converter in a small package that can be used in any single-cell Li-ion application. This IC provides protection features such as input undervoltage lockout, short circuit, and overtemperature shutdown. The IC transitions to skip mode seamlessly under lightload conditions to improve efficiency. Under these conditions, switching occurs only as needed, reducing switching frequency and supply current to maintain high efficiency. When the input voltage is sufficient to drive the load, the IC can be operated in track mode or automatic track mode (ATM). In track mode, the p-channel MOSFET acts as a current-limited load switch and quiescent current is as low as 30µA under a no-load condition. In ATM mode, the p-channel MOSFET acts as a current-limited load switch and quiescent current is as low as 60µA under a no-load condition. In ATM mode, the internal boost circuitry is enabled, allowing for fast transitions into boost mode. The IC is available in a small, 1.25mm x 1.25mm, 9-bump WLP (0.4mm pitch) package. Applications Cell Phones Features S Compact Layout Small, 1.25mm x 1.25mm WLP Package 3MHz PWM Switching Frequency Small External Components S Safe and Efficient Step-Up Mode Up to 1A Output Current 2.5V to 5.5V Input Voltage Range 3.3V to 5V Ouput Voltage Range Over 90% Efficiency with Internal Synchronous_ Rectifier Low 45µA No-Load Quiescent Current Soft-Start Controls Inrush Current True Shutdown™ Low 1µA Shutdown Current S Track Mode 1A Current Limited 130mI On-Resistance Low 30µA No Load Quiescent Current S Automatic Track Mode 130mI On-Resistance Low 60µA No-Load Quiescent Current Boost Circuitry Enabled for Fast Transition into_ Boost Smartphones Mobile Internet Devices GPS, PND eBooks Typical Operating Circuit L1 1µH INPUT 2.5V TO 5.5V CIN 4.7µF IN LX_ OUT_ OUTPUT 3.7V, 1A COUT 22µF MAX8969 Ordering Information PART VOUT (V) TEMP RANGE PINPACKAGE MAX8969EWL33+ 3.3 -40NC to +85NC 9 WLP MAX8969EWL35+ 3.5 -40NC to +85NC 9 WLP MAX8969EWL37+ 3.7 -40NC to +85NC 9 WLP MAX8969EWL42+ 4.25 -40NC to +85NC 9 WLP MAX8969EWL50+ 5.0 -40NC to +85NC 9 WLP Note: The output voltage range is from 3.3V to 5V. Contact the factory for output options and availability. +Denotes a lead(Pb)-free/RoHS-compliant package. EN TREN GND_ True Shutdown is a trademark of Maxim Integrated Products, Inc. ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX8969 General Description MAX8969 Step-Up Converter for Handheld Applications ABSOLUTE MAXIMUM RATINGS IN, OUT_ to GND_.................................................-0.3V to +6.0V EN, TREN to GND_............. -0.3V to lower of (VIN + 0.3V) or 6V Total LX_ Current............................................................ 3.2ARMS OUT_ Short Circuit to GND_......................................Continuous Continuous Power Dissipation (TA = +70NC) WLP (derate 12mW/NC above +70NC).........................960mW Operating Temperature Range........................... -40NC to +85NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -65NC to +150NC Soldering Temperature (reflow) (Note 1).........................+260NC Note 1: This device is constructed using a unique set of packaging techniques that impose a limit on the thermal profile that the device can be exposed to during board level solder attach and rework. This limit permits only the use of the solder profiles recommended in the industry-standard specification JEDEC 020A, paragraph 7.6, Table 3 for IR/VPR and Convection reflow. Preheating is required. Hand or wave soldering is not allowed. Stresses beyond those listed under “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 for extended periods may affect device reliability. PACKAGE THERMAL CHARACTERISTICS (Note 2) WLP Junction-to-Ambient Thermal Resistance (BJA)...........83NC/W Junction-to-Case Thermal Resistance (BJC)................50NC/W Note 2: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. ELECTRICAL CHARACTERISTICS (VIN = 2.6V, TA = -40NC to +85NC, unless otherwise noted. Typical values are TA = +25NC.) (Note 3) PARAMETER CONDITIONS MIN Operating Input Voltage Range TYP 2.5 Minimum Startup Voltage MAX UNITS 5.5 V 2.3 Undervoltage Lockout Threshold (UVLO) VIN falling, 75mV hysteresis Shutdown Supply Current VEN = VTREN = VOUT = 0V, VIN = 4.8V Thermal Shutdown TA rising, 20NC hysteresis 2.1 V 2.2 2.3 TA = +25NC 0.8 5 TA = +85NC 1 +165 V FA NC BOOST MODE Continuous Output Current Peak Output Current Switching Frequency Output Voltage Accuracy VIN > 2.5V (Note 4) VIN > 2.5V, pulse load 1 VOUT = 3.3V 0.9 VOUT = 3.5V 0.8 VOUT = 3.7V 0.7 VOUT = 4.25V 0.7 VOUT = 4.7V 0.7 VOUT = 5.0V 0.7 (Note 4) A A 3 MHz No load, VOUT_TARGET = 3.3V 3.175 3.30 3.40 No load, VOUT_TARGET = 3.5V 3.40 3.50 3.60 No load, VOUT_TARGET = 3.7V 3.64 3.75 3.85 No load, VOUT_TARGET = 4.25V 4.10 4.25 4.35 No load, VOUT_TARGET = 5V 4.85 5.00 5.10 2 _______________________________________________________________________________________ V Step-Up Converter for Handheld Applications (VIN = 2.6V, TA = -40NC to +85NC, unless otherwise noted. Typical values are TA = +25NC.) (Note 3) PARAMETER Steady-State Output Voltage (Notes 5, 6) CONDITIONS MIN TYP 2.5V < VIN < VATMRT, conditions emulating 0 < IOUT < 1A, COUT = 22FF, L = 1FH, VOUT_TARGET = 3.3V 3.00 3.45 2.5V < VIN < VATMRT, conditions emulating 0 < IOUT < 1A, COUT = 22FF, L = 1FH, VOUT_TARGET = 3.5V 3.15 3.65 2.5V < VIN < VATMRT, conditions emulating 0 < IOUT < 1A, COUT = 22FF, L = 1FH, VOUT_TARGET = 3.7V 3.35 3.85 2.5V < VIN < VATMRT, conditions emulating 0 < IOUT < 600mA, COUT = 22FF, L = 1FH, VOUT_TARGET = 4.25V 3.95 4.35 2.5V < VIN < VATMRT, conditions emulating 0 < IOUT < 500mA, COUT = 22FF, L = 1FH, VOUT_TARGET = 5V 4.50 5.10 TA = +25NC 0.1 TA = +85NC 0.2 LX_ Leakage Current VLX = 0V, 4.8V Skip-Mode Supply Current EN = high, IOUT = 0A, 1FH inductor (TREN is low, not switching) 10 LX_ nMOS Current Limit 2.6 Maximum Duty Cycle pMOS On-Resistance nMOS On-Resistance 83 0 120 VOUT = 3.5V 115 VOUT = 3.7V 110 VOUT = 4.25V 100 VOUT = 5V 91 VOUT = 3.3V 65 VOUT = 3.5V 63 VOUT = 3.7V 60 VOUT = 4.25V 55 VOUT = 5V 51 Maximum Output Capacitance (Actual) 8 0 < IOUT < 0.3A during startup UNITS V FA FA mA 3.2 A % % VOUT = 3.3V Minimum Output Capacitance for Stable Operation (Actual) 5 45 pMOS Turn-Off Current (Zero-Cross Current) Minimum Duty Cycle MAX VOUT = 3.3V 70 VOUT = 3.5V 55 VOUT = 3.7V 45 VOUT = 4.25V 30 VOUT = 5V 20 mI mI FF FF _______________________________________________________________________________________ 3 MAX8969 ELECTRICAL CHARACTERISTICS (continued) MAX8969 Step-Up Converter for Handheld Applications ELECTRICAL CHARACTERISTICS (continued) (VIN = 2.6V, TA = -40NC to +85NC, unless otherwise noted. Typical values are TA = +25NC.) (Note 3) PARAMETER CONDITIONS MIN Output Voltage Ripple IOUT = 150mA, circuit of Figure 1 Soft-Start Interval IOUT = 10mA, see the Output Capacitor Selection section TYP MAX 20 UNITS mVP-P Fs TRACK MODE pMOSFET On-Resistance IOUT = 500mA, VIN = 2.7V 130 IOUT = 500mA, VIN = 3.2V 110 Track Current Limit VOUT = 3.6V Track Mode Quiescent Current EN = low, TREN = high 1 mI 2 A 30 FA 65 FA AUTOMATIC TRACK MODE (ATM) ATM Supply Current ATM VIN Rising Threshold (VATMRT) ATM VIN Falling Threshold (VATMFT) Boost to ATM Transition Time VIN = 5.4V VOUT_TARGET = 3.3V 3.15 VOUT_TARGET = 3.5V 3.35 VOUT_TARGET = 3.7V 3.55 VOUT_TARGET = 4.25V 4.04 VOUT_TARGET = 5V 4.74 VOUT_TARGET = 3.3V 3.10 VOUT_TARGET = 3.5V 3.29 VOUT_TARGET = 3.7V 3.5 VOUT_TARGET = 4.25V 3.99 VOUT_TARGET = 5V 4.69 (Note 7) ATM to Boost Transition Time V V 1 Fs 1 Fs LOGIC CONTROL EN, TREN Logic Input High Voltage 2.3V < VIN < 5.5V EN, TREN Logic Input Low Voltage 2.3V < VIN < 5.5V EN, TREN Leakage Current VEN = VTREN = 0V 1.05 V 0.4 TA = +25NC TA = +85NC -1 0.01 0.1 +1 V FA Note 3: Specifications are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design and characterization. Note 4: Continuous operation with 1A at elevated ambient temperature and low voltage is not guaranteed. Under worst-case conditions, die thermal protection cannot be activated after 100ms of 1A load application. See the continuous output current parameter for a conservative estimate of current that can be maintained at TA = +85°C. Note 5: Switching frequency decreases if input voltage is > 83% of the output voltage selected. This allows duty factor to drop to values necessary to boost output voltage less than 25% without the use of pulse widths less than 60ns. Note 6: Contact factory for other options. Note 7: The output voltage regulation is a direct function of the peak current in the nMOS power switch. The inductor current (ILX) described in the conditions of the steady-state output voltage specification corresponds to the peak inductor current. Note 8: Once ATM threshold is reached boost switching stops in 1µs (typ), but the transition to ATM does not occur until VOUT has fallen equal to VIN. 4 _______________________________________________________________________________________ Step-Up Converter for Handheld Applications EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.7V) 95 96 EFFICIENCY (%) VIN = 3.1V VIN = 2.5V VIN = 3.6V 75 90 VIN = 2.5V 88 86 70 84 65 82 L = TOKO DFE252012 1µH 60 1 10 100 80 1 10 50 40 VOUT = 3.7V 30 20 0 2.5 1000 100 VOUT = 5V 60 10 L = TOKO DFE252012 1µH 1000 3.0 3.5 4.0 4.5 5.0 LOAD CURRENT (mA) LOAD CURRENT (mA) INPUT VOLTAGE (V) MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE OUTPUT VOLTAGE (VOUT = 5V) vs. OUTPUT CURRENT OUTPUT VOLTAGE (VOUT = 3.7V) vs. OUTPUT CURRENT 2000 1500 1000 500 3.5 4.0 4.85 4.80 VIN = 3.2V 4.75 4.70 4.5 5.0 4.55 5.5 0 200 400 600 800 OUTPUT VOLTAGE (V) 5.0 4.0 VIN = 3.2V 3.8 3.6 VIN = 3.6V 3.2 1000 0 200 400 600 800 1000 OUTPUT CURRENT (mA) OUTPUT VOLTAGE (VOUT = 3.7V) vs. INPUT VOLTAGE 5.0 AUTOMATIC IOUT = 1000mA FREQUENCY AUTOMATIC ADJUSTMENT TRACK MODE TRANSITION AUTOMATIC TRACK MODE TRANSITION IOUT = 100mA 4.5 OUTPUT VOLTAGE (V) IOUT = 10mA I OUT = 100mA IOUT = 600mA VIN = 4.3V VIN = 2.5V OUTPUT CURRENT (mA) OUTPUT VOLTAGE (VOUT = 5V) vs. INPUT VOLTAGE 4.5 4.0 3.4 VIN = 2.5V INPUT VOLTAGE (V) 5.5 4.2 4.90 4.60 3.0 VIN = 4.3V 4.65 VOUT, 3.7V ≥ 3.35V 2.5 4.4 5.5 MAX8969 toc06 VIN = 3.6V 4.95 OUTPUT VOLTAGE (V) 2500 5.00 OUTPUT VOLTAGE (V) VOUT, 5V ≥ 4.5V MAX8969 toc05 5.05 MAX8969 toc04 3000 MAXIMUM OUTPUT CURRENT (mA) 92 70 IOUT = 10mA 4.0 IOUT = 1000mA 3.5 IOUT = 600mA 3.0 3.5 MAX8969 toc08 80 80 94 MAX8969 toc07 EFFICIENCY (%) 90 85 VIN = 3.1V 98 MAX8969 toc03 VIN = 4.3V MAX8969 toc02 100 MAX8969 toc01 100 NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE NO-LOAD SUPPLY CURRENT (uA) EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5V) AUTOMATIC FREQUENCY ADJUSTMENT 2.5 3.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) 5.0 5.5 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5 MAX8969 Typical Operating Characteristics (VIN = 3.6V, COUT = 22µF, X5R, 6.3V local and 10µF, X5R, 6.3V, 1µH inductor, circuit of Figure 1, TA = +25NC, unless otherwise noted.) MAX8969 Step-Up Converter for Handheld Applications Typical Operating Characteristics (continued) (VIN = 3.6V, COUT = 22µF, X5R, 6.3V local and 10µF, X5R, 6.3V, 1µH inductor, circuit of Figure 1, TA = +25NC, unless otherwise noted.) 3.7V LINE TRANSIENT 5V LINE TRANSIENT MAX8969 toc10 MAX8969 toc09 3V VIN 3.7V 2.6V VIN AC-COUPLED 100mV/div VOUT 3.3V AC-COUPLED 100mV/div VOUT TREN = VIN, IOUT = 200mA TREN = VIN, IOUT = 200mA 100µs/div 100µs/div 3.7V LOAD TRANSIENT (0mA-50mA-0mA) 5V LOAD TRANSIENT (0mA-50mA-0mA) MAX8969 toc11 MAX8969 toc12 AC-COUPLED 50mV/div VOUT VLX 5V/div 0 AC-COUPLED 50mV/div VOUT VLX 5V/div 0 50mA IOUT 0 50mA 0 IOUT VIN = 2.6V VIN = 3.8V 200µs/div 200µs/div 3.7V LOAD TRANSIENT (50mA-500mA-50mA) 5V LOAD TRANSIENT (50mA-500mA-50mA) MAX8969 toc13 MAX8969 toc14 AC-COUPLED 200mV/div VOUT 5V/div 0 VLX AC-COUPLED 100mV/div VOUT 5V/div 0 VLX 500mA 500mA IOUT 50mA VIN = 2.8V 50mA IOUT VIN = 3.8V 20µs/div 20µs/div 6 _______________________________________________________________________________________ Step-Up Converter for Handheld Applications STARTUP (VOUT = 3.7V) LIGHT-LOAD RIPPLE MAX8969 toc16 MAX8969 toc15 2V/div AC-COUPLED 20mV/div VOUT 2V/div VLX VEN COUT, TYP = 32µF, TREN = GND, IOUT = 10mA, VIN = 2.6V 0 2V/div 0 VOUT 2V/div 0 IOUT = 1mA, VIN = 3.6V VLX 0 200µs/div 40µs/div STARTUP (VOUT = 5V) HARD-SHORT (VOUT = 3.7V) MAX8969 toc18 MAX8969 toc17 VOUT 2V/div 2V/div VEN COUT, TYP = 32µF, TREN = GND, IOUT = 10mA, VIN = 3.2V 0 0 2A/div 2V/div 0 VOUT IOUT VLX 2V/div VLX 0 0 2V/div VIN = 3.2V, 0.1I LOAD ILX HARD-SHORT (VOUT = 5V) 0 SHUTDOWN MAX8969 toc19 MAX8969 toc20 VOUT 2V/div IOUT 0 2A/div 0 VEN 2V/div 0 VOUT 2V/div VLX 0 2V/div 2V/div VLX 0 20µs/div 0 2A/div 0 ILX 2A/div 40µs/div 200µs/div VIN = 3.2V, 0.1I LOAD 0 10I LOAD, TREN = GND 2µs/div _______________________________________________________________________________________ 7 MAX8969 Typical Operating Characteristics (VIN = 3.6V, COUT = 22µF, X5R, 6.3V local and 10µF, X5R, 6.3V, 1µH inductor, circuit of Figure 1, TA = +25NC, unless otherwise noted.) Step-Up Converter for Handheld Applications MAX8969 Pin Configuration TOP VIEW (BUMP SIDE DOWN) MAX8969 1 2 3 A OUT1 OUT2 IN B LX1 LX2 EN C GND1 GND2 TREN + WLP (1.25mm × 1.25mm) Pin Description PIN NAME FUNCTION A1 OUT1 A2 OUT2 Power Output. Bypass OUT_ to ground with a 22FF rated ceramic capacitor. For optimal performance place the ceramic capacitor as close as possible to OUT_. OUT1 and OUT2 should be shorted together directly under the IC. In True Shutdown, the output voltage can fall to 0V, but OUT_ has a diode with its cathode connected to IN. See Figure 3. A3 IN B1 LX1 B2 LX2 B3 EN C1 GND1 C2 GND2 C3 TREN Input Supply Voltage. Bypass IN to GND_ with a 4.7FF ceramic capacitor. A larger capacitance may be required to reduce noise. Converter Switching Node. Connect a 1FH inductor from LX_ to IN. LX_ is high impedance in shutdown. LX1 and LX2 should be shorted together directly under the IC. Enable Input. Drive EN logic-high to enable boost mode, regardless of the logic level of TREN. Connect EN to ground or drive logic-low to allow TREN to select either True Shutdown or track mode. See Table 1. Ground. Connect GND_ to a large ground plane. GND1 and GND2 should be shorted together directly under the IC. Track Enable Input. Drive TREN logic-high to enable track mode. Connect TREN to ground or drive logic-low to place the IC in True Shutdown. See Table 1. 8 _______________________________________________________________________________________ Step-Up Converter for Handheld Applications COUT 22µF MAX8969 IN REFERENCE CIN 4.7µF RAMP GENERATOR ATM COMPARATOR IN IN P1 ATM 0.95 x VOUT_TARGET TRACK CONTROL LOGIC PWM LOGIC TRUE SHUTDOWN N1 ENABLE TREN CURRENT LIMIT EN L1 1µH GND_ LX_ Figure 1. Functional Diagram Detailed Description The MAX8969 is a step-up DC-DC switching converter that utilizes a fixed-frequency PWM architecture with True Shutdown. With an advanced voltage-positioning control scheme and high 3MHz switching frequency, the IC is inexpensive to implement and compact, using only a few small easily obtained external components. Under light-load conditions, the IC switches only when needed, consuming only 45FA (typ) of quiescent current. The IC is highly efficient with an internal switch and synchronous rectifier. Shutdown typically reduces the quiescent current to 1FA (typ). Low quiescent current and high efficiency make this device ideal for powering portable equipment. Internal soft-start limits inrush current to less than 720mA (typ), while output voltage is less than input voltage. Once output voltage approaches input voltage approaches input voltage after a brief delay, output voltage is boosted to its final value at a rate of approximately 25mV/µs. During this period, as well as being limited by the voltage, ramp rate current is limited by the normal 2.6A boost mode current limit. In boost mode, the step-up converter boosts to VOUT_TARGET from battery input voltages ranging from 2.5V to VOUT_TARGET. When the input voltage ranges from 0.95 x VOUT_TARGET to 5.5V, the IC enters ATM and the output voltage approximately follows the input voltage. During boost mode, the input current limit is set to 2.6A to guarantee delivery of the rated out current (e.g., 1A output current when boosting from a 2.5V input supply to a 3.7V output). Control Scheme The step-up converter uses a load/line control scheme. The load/line control scheme allows the output voltage to sag under load, but prevents overshoot when the load is suddenly removed. The load/line control scheme reduces the total range of voltages reached during transients at the expense of DC output impedance. _______________________________________________________________________________________ 9 MAX8969 OUT_ MAX8969 Step-Up Converter for Handheld Applications UVLO, EXCESSIVE TEMPERATURE, OR SHORT CIRCUIT FROM ANY STATE TRUE SHUTDOWN N1 = OFF P1 = OFF IQ = 1µA (typ) EN = 1, OR TREN = 1 0 VIN COMPARATOR 1 EN = 0, TREN = 0 EN = 0, TREN = 0 AUTOMATIC TRACK MODE (ATM)* TRACK MODE* VOUT < VIN, TREN = 0 N1 = OFF P1 = CURRENTLIMITED SWITCH IQ = 30µA (typ) VOUT < VIN, TREN = 1 EN = 1, VOUT > (VIN - 300mV) BOOST EXIT MODE N1 = OFF P1 = OFF IC WAITS UNTIL VOUT = VIN N1 = OFF P1 = CURRENTLIMITED SWITCH IQ = 65µA (typ) BOOST CIRCUITRY ENABLED EN = 0 BOOST SOFT-START VIN COMPARATOR = 0 OUTPUT BELOW TARGET [VOUT < (0.72 x VOUT_TARGET)] VIN COMPARATOR = 1 N1 = SWITCHING P1 = OFF EN = 0 SOFT-START VOLTAGE RAMP COMPLETE BOOST MODE N1 = SWITCHING P1 = SWITCHING VOUT = VOUT_TARGET IQ = 45µA (SKIP MODE) *EN TAKES PRIORITY OVER TREN. SEE TABLE 1. Figure 2. State Diagram 10 ������������������������������������������������������������������������������������� Step-Up Converter for Handheld Applications P1 BODY DIODE LX_ OUT_ IN N1 = OFF P1 = OFF TRACK/ATM MODE: P1 BODY DIODE LX_ OUT_ IN N1 = OFF P1 = CURRENTLIMITED SWITCH BOOST SOFT-START: P1 BODY DIODE LX_ OUT_ IN N1 = SWITCHING P1 = OFF BOOST MODE: P1 BODY DIODE LX_ OUT_ IN N1 = SWITCHING P1 = SWITCHING BOOST EXIT MODE: P1 BODY DIODE LX_ OUT_ IN N1 = OFF P1 = OFF Figure 3. Modes of Operation ______________________________________________________________________________________ 11 MAX8969 TRUE SHUTDOWN: MAX8969 Step-Up Converter for Handheld Applications The IC is designed to operate with the input voltage range straddling its output voltage set point. Two techniques are used to accomplish this. The first technique is to activate ATM if the input voltage exceeds 95% of the output set point; see the Automatic Track Mode (ATM) section. The second technique is automatic frequency adjustment. Automatic Track Mode (ATM) ATM is entered when an internal comparator signals that the input voltage has exceeded the ATM threshold. The ATM threshold is 95% of the output voltage target. At this point, the IC enters ATM, with the pMOS switch turned on, regardless of the status of TREN. Note that EN must be high to enable ATM mode. This behavior is summarized in Table 1. Automatic Frequency Adjustment Automatic frequency adjustment is used to maintain stability if the input voltage is above 80% and below 95% of the output set point. Frequency adjustment is required because the n-channel has a minimum on-time of approximately 60ns. At 3MHz, this would lead to the p-channel having a maximum duty factor of 82%. With an input voltage more than 82% of the output set point, the p-channel’s duty factor must be increased by reducing operating frequency either through cycle skipping or adjusting the clock’s frequency. The IC adjusts its clock frequency rather than simply skipping cycles. This adjustment is done in two steps. The first step occurs if the input voltage exceeds approximately 83% of the output voltage and reduces clock speed to approximately 1.6MHz. The second step occurs if the input voltage is greater than output voltage less 460mV. If this condition is met, clock frequency is reduced to approximately 1MHz. Frequency adjustment allows the converter to operate at a known frequency under all conditions. Fault Protection In track, ATM, and boost modes, the IC has protection against overload and overheating. • In track and ATM, current is limited to prevent excessive inrush current during soft-start and to protect against overload conditions. If the die temperature exceeds +165°C in track/ATM, the switch turns off until the die temperature has cooled to +145NC. • In boost mode, during each 3MHz switching cycle, if the inductor current exceeds 2.6A, the n-channel MOSFET is shut off and the p-channel MOSFET is switched on. The end result is that LX_ current is regulated to 2.6A or less. A 2.6A inductor current is a large enough current to guarantee a 1A output load current under all intended operating conditions. The IC can operate indefinitely while regulating the inductor current to 2.6A or less. However, if a short circuit or extremely heavy load is applied to the output, the output voltage decreases since the inductor current is limited to 2.6A. If the output voltage decreases to less than 72% of the regulation voltage target (i.e., 2.8V with VOUT_TARGET of 3.7V), a short circuit is assumed, and the IC returns to the shutdown state. The IC then attempts to start up if the output short is removed. Even if the output short persists indefinitely, the IC thermal protection ensures that the die is not damaged. True Shutdown During operation in boost mode, the p-channel MOSFET prevents current from flowing from OUT_ to LX_. In all other modes of operation, it is desirable to block current flowing from LX_ to OUT_. True Shutdown prevents current from flowing from LX_ to OUT_ while the IC is shut down by reversing the internal body diode of the p-channel MOSFET. This feature is also active during track/ATM to allow current limit to function as anticipated. Upon leaving boost mode, the p-channel MOSFET continues to prevent current from flowing from OUT_ to LX_ until OUT_ and IN are approximately the same voltage. After this condition has been met, track/ATM and shutdown operate normally. Table 1. Modes of Operation VIN COMPARATOR EN TREN MODE OF OPERATION X 0 0 True Shutdown X 0 1 Track 0 1 X Boost 1 1 X ATM X = Don't care. 12 ������������������������������������������������������������������������������������� Step-Up Converter for Handheld Applications The maximum power dissipation depends on the thermal resistance of the IC package and circuit board. The power dissipated (PD) in the device is: PD = POUT x (1/E - 1) where E is the efficiency of the converter and POUT is the output power of the step-up converter. The maximum allowed power dissipation is: Input Capacitor Selection The input capacitor (CIN) reduces the current peaks drawn from the battery or input power source. The impedance of CIN at the switching frequency should be kept very low. Ceramic capacitors with X5R or X7R temperature characteristics are highly recommended due to their small size, low ESR, and small temperature coefficients. Note that some ceramic dielectrics exhibit large capacitance and ESR variation with temperature and DC bias. Ceramic capacitors with Z5U or Y5V temperature characteristics should be avoided. A 4.7FF input capacitor is recommended for most applications. This assumes that the input power source has at least 22FF of additional capacitance near the IC. For optimum noise immunity and low input-voltage ripple, the input capacitor value can be increased. PMAX = (TJMAX - TA)/BJA where (TJMAX - TA) is the temperature difference between the IC’s maximum rated junction temperature and the surrounding air, and BJA is the thermal resistance of the junction through the PCB, copper traces, and other materials to the surrounding air. Applications Information Step-Up Inductor Selection Recommended PCB Layout and Routing Poor layout can affect the IC performance, causing electromagnetic interference (EMI) and electromagnetic compatibility (EMC) performance, ground bounce, and voltage losses. Poor layout can also affect regulation and stability. A good layout is implemented using the following rules: • Place the inductor, input capacitor, and output capacitor close to the IC using short traces. These components carry high switching frequencies and large traces act like antennas. The output capacitor placement is the most important in the PCB layout and should be placed directly next to the IC. The inductor and input capacitor placement are secondary to the output capacitor’s placement but should remain close to the IC. • Route the output voltage path away from the inductor and LX_ switching node to minimize noise and magnetic interference. • Maximize the size of the ground metal on the component side to help with thermal dissipation. Use a ground plane with several vias connecting to the component-side ground to further reduce noise interference on sensitive circuit nodes. Due to the small size of the recommended capacitor, the inductor’s value is limited to approximately 1FH. Inductors of approximately 1FH guarantee stable operation of the converter with capacitance as small as 8FF (actual) present on the converter’s output. If the inductor’s value is reduced significantly below 1FH, ripple can become excessive. Output Capacitor Selection An output capacitor (COUT) is required to keep the output-voltage ripple small and to ensure regulation loop stability. The output capacitor must have low impedance at the switching frequency. Ceramic capacitors are highly recommended due to their small size and low ESR. Ceramic capacitors with X5R or X7R temperature characteristics generally perform well. One 22FF (with a minimum actual capacitance of 6FF under operating conditions) is recommended. This capacitor along with an additional 10FF of bypass capacitance, associated with the load, guarantee proper performance of the IC. The minimum combined capacitance is required to be 8FF or larger. These capacitors can be found with case size 0603 or larger. Refer to the MAX8969 Evaluation Kit for more details. Chip Information PROCESS: BiCMOS ______________________________________________________________________________________ 13 MAX8969 Thermal Considerations In most applications, the IC does not dissipate much heat due to its high efficiency. But in applications where the IC runs at high ambient temperature with heavy loads, the heat dissipated may cause the temperature to exceed the maximum junction temperature of the part. If the junction temperature reaches approximately +165NC, the thermal overload protection is activated. MAX8969 Step-Up Converter for Handheld Applications Package Information For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 9 WLP W91B1+7 21-0459 Refer to Application Note 1891 14 ������������������������������������������������������������������������������������� Step-Up Converter for Handheld Applications REVISION NUMBER REVISION DATE 0 9/11 DESCRIPTION Initial release PAGES CHANGED — Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2011 Maxim Integrated Products 15 Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX8969 Revision History