19-3637; Rev 0; 4/05 ILABLE N KIT AVA EVALUATIO Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones Features The MAX8622 flyback switching regulator quickly and efficiently charges high-voltage photoflash capacitors. It is ideal for use in digital, film, cell-phone, and smartphone cameras that use either 2-cell alkaline/NiMH or single-cell Li+ batteries. An internal, low-on-resistance n-channel MOSFET improves efficiency by lowering switch power loss. Charges Any Size Photoflash Capacitor A current-limited, continuous-mode, transformer-switching scheme quickly charges the output capacitor. The cycle-by-cycle peak current-limit scheme has no inrush current. Current limit is programmable to control the maximum load drawn from the battery. An additional input-voltage monitor loop extends battery life by reducing the charge rate when the battery is nearly discharged. This also permits the current limit to be set for a faster charge rate under typical conditions, rather than a level dictated by the worst-case discharge state of the battery. Extends Battery Life with Input Voltage Monitoring No Inrush Current High Accuracy Not Dependent on Transformer Turns Ratio Programmable Input Current Limit Up to 1.6A Robust Architecture Allows Use of Low-Cost Transformers Automatic Refresh Mode Charge-Done Indicator Small, 3mm x 3mm, 10-Pin TDFN Package The MAX8622 provides high charge accuracy by using an external resistor-divider to monitor the output voltage. Sensing directly at the transformer secondary prevents output-capacitor discharge through feedback resistors while still providing direct output sensing for optimum voltage accuracy that is not transformer turns-ratio dependent. The MAX8622 is offered in a 3mm x 3mm 10-pin TDFN package. EN DONE SEC LX TOP VIEW UVI Pin Configuration 10 9 8 7 6 1 2 3 4 5 FB VCC GND PGND MAX8622 ISET An open-drain DONE output indicates when the photoflash capacitor is completely charged. The MAX8622 automatically refreshes the output every 11s, efficiently maintaining the capacitor charge level with minimum battery drain. 2.8s to Charge 100F to 300V TDFN 3mm x 3mm Applications Digital Cameras Typical Operating Circuit Cell-Phone Cameras Film Cameras VIN 1.5V TO 5.5V Smartphone Cameras OUTPUT 300V Personal Media Players 1:15 VCC 2.5V TO 5.5V Ordering Information PART MAX8622ETB+ TEMP RANGE -40C to +85C PIN-PACKAGE 10 TDFN 3mm x 3mm (T1033-1) UVI VCC LX SEC FB MAX8622 TOP MARK PGND DONE APF ISET GND EN +Indicates lead-free packaging. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX8622 General Description MAX8622 Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones ABSOLUTE MAXIMUM RATINGS LX to PGND ............................................................-0.3V to +33V DONE, VCC, UVI to GND ..........................................-0.3V to +6V FB, EN, ISET to GND ..................................-0.3V to (VCC + 0.3V) PGND to GND ...................................................... -0.3V to +0.3V SEC Current................................................................... 200mA DONE Current...................................................................25mA Continuous Power Dissipation (TA = +70C) TDFN (derate 18.5mW/C above +70C)...................1481mW Operating Temperature Range ...........................-40C to +85C Junction Temperature Range ............................-40C to +125C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C 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. ELECTRICAL CHARACTERISTICS (VCC = VEN = 3.3V, VFB = 0V, RISET = 75k, VUVI = 1.5V, TA = -40C to +85C. Typical values are at TA = +25C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS VCC Voltage Range VCC Undervoltage Threshold VCC Supply Current MIN 2.180 2.300 2.425 2.210 2.325 LX switching at 40kHz 1 LX switching at 300kHz 1.65 LX On-Resistance ILX = 200mA LX Off-Leakage VLX = 5.5V, VEN = 0V 60 100 0.1 1 TA = +85C 0.1 VCC = 3.3V 0.31 0.5 VCC = 2.5V 0.35 0.6 TA = +25C 0.1 1 TA = +85C 0.1 RISET = 200k, TA = 0C to +85C 0.54 0.61 0.72 RISET = 75k, TA = 0C to +85C 1.44 1.60 1.76 ISET = VCC, TA = 0C to +85C 1.44 1.60 1.76 Circuit of Figure 2, output 90% of final value A mA 27 TA = 0C to +85C 1.238 1.250 1.262 TA = -40C to +85C 1.231 1.250 1.269 TA = +25C 0.1 1 TA = +85C 0.1 VFB rising FB Input Current VFB = 1.25V and EN = high, or VEN = VFB = 0V Output Refresh Rate From FB pulsed high to LX switching restarts 2 A 27 Sets peak current limit from 0.6A to 1.6A VEN = 0V 1.7 ISEC falling, RISET = 75k FB Trip Threshold ISET Voltage A kHz 10 VEN = VCC A 300 ISEC falling, RISET = 200k ISEC falling, ISET = VCC V mA TA = +25C SEC Sense Resistance ISET Resistance Range V 2.095 VEN = 0V, VCC = 5.5V SEC Valley Current Threshold UNITS 5.5 VCC falling VCC Shutdown Current Switching Frequency MAX VCC rising LX not switching, VCC = 5.5V LX Peak Current Limit TYP 2.5 11 75 0 _______________________________________________________________________________________ A s 200 1.0 V k V Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones (VCC = VEN = 3.3V, VFB = 0V, RISET = 75k, VUVI = 1.5V, TA = -40C to +85C. Typical values are at TA = +25C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX 1.96 2.00 2.04 UVI Trip Threshold Falling External 25k resistor in series with UVI TA = 0C to +85C TA = -40C to +85C 1.94 2.00 2.06 UVI Trip Threshold Rising External 25k resistor in series with UVI TA = 0C to +85C 2.10 2.14 2.18 TA = -40C to +85C 2.08 2.14 2.20 UVI Pulldown Resistance 25 UVI Input Current VEN = 0V, VUVI = VCC = 5.5V EN Input Voltage When charging starts/stops EN Input Leakage Current VEN = 0 to 5.5V DONE Output-Voltage Low IDONE = 5mA DONE Output-Current High VDONE = 5.5V TA = +25C 0.1 TA = +85C 0.1 VIH VIL 0.4 0.1 TA = +85C 0.1 V V k 1 1.4 TA = +25C UNITS 1 40 150 TA = +25C 0.1 1 TA = +85C 0.1 A V A mV A Note 1: Limits are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed by design and characterization. _______________________________________________________________________________________ 3 MAX8622 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = VIN = VEN = 3.5V, circuit of Figure 2, TA = +25C, unless otherwise noted.) CHARGE TIME (FROM 30V TO 300V) vs. INPUT VOLTAGE (800mA PEAK) RISET = 150k 100F CHARGE TIME (s) 150F 4 3 2 70 150F 10 50F 4.5 2.5 5.5 40 30 COUT = 150F 0 0 3.5 2.5 VIN = 3.5V 50 10 50F 0 60 20 5 1 3.5 4.5 50 0 5.5 100 150 200 250 INPUT VOLTAGE (V) INPUT VOLTAGE (V) OUTPUT VOLTAGE (V) OUTPUT VOLTAGE VS. INPUT VOLTAGE OUTPUT VOLTAGE vs. TEMPERATURE PRIMARY CURRENT LIMIT vs. ISET RESISTOR 320 310 300 310 VIN = 3.5V AND 5V 305 300 290 295 280 290 MAX8622 toc06 315 OUTPUT VOLTAGE (V) 330 300 2.0 1.8 PRIMARY CURRENT LIMIT (A) 320 MAX8622 toc04 340 OUTPUT VOLTAGE (V) 100F 15 MAX8622 toc05 CHARGE TIME (s) 5 VIN = 5V 80 EFFICIENCY (%) 20 6 90 MAX8622 toc02 ISET = VCC 7 EFFICIENCY vs. OUTPUT VOLTAGE 25 MAX8622 toc01 8 MAX8622 toc03 CHARGE TIME (FROM 30V TO 300V) vs. INPUT VOLTAGE (1.6A PEAK) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 3.4 4.1 4.8 -15 10 35 60 75 100 125 150 175 200 TEMPERATURE (C) ISET RESISTOR (k) PRIMARY CURRENT LIMIT vs. TEMPERATURE PEAK PRIMARY CURRENT vs. INPUT VOLTAGE QUIESCENT CURRENT vs. INPUT VOLTAGE AFTER CHARGE COMPLETE 1.60 1.55 1.50 1.45 ISET = VCC 1.6 1.4 1.2 1.0 0.8 0.6 -15 10 35 TEMPERATURE (C) 60 85 180 160 140 120 100 80 60 0.4 40 0.2 20 0.0 1.35 200 QUIESCENT CURRENT (A) PEAK PRIMARY CURRENT (A) 1.65 1.40 1.8 MAX8622 toc09 2.0 MAX8622 toc07 1.70 -40 50 85 INPUT VOLTAGE (V) 1.75 4 0.0 -40 5.5 MAX8622 toc08 2.7 PRIMARY CURRENT LIMIT (A) MAX8622 Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones RISET = 75k 0 2.7 3.4 4.1 INPUT VOLTAGE (V) 4.8 5.5 2.5 3.5 4.5 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5.5 Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones SWITCHING WAVEFORMS LINE STEP THROUGH UVI MAX8622 toc10 CHARGE PROFILE MAX8622 toc11 MAX8622 toc12 10V/div VLX VIN 0 5V/div VEN 500mV/div 5V/div VDONE VLX IPRI 10V/div 0 1A/div 1A/div 0 IPRI 0 100mA/div 0 ISEC 100V/div VOUT C3 = 150F 0 VOUT = 100V 1s/div 20s/div VIN = 2.4V TO 2.0V TO 2.4V, VCC = 3.5V, VOUT = 100V, RUVI = 25k 1s/div Pin Description PIN NAME FUNCTION 1 ISET Current-Limit Set. Connect a resistor from ISET to GND to set the peak current limit through the primary winding (RISET = 1.6A x 75k / IPEAK), or connect ISET directly to VCC for the default current limit of 1.6A. 2 FB Output Feedback. Connect FB to a resistor-divider from the transformer secondary winding to set the output voltage at which charging is complete. 3 VCC Supply Voltage for the IC. Connect a 1F capacitor from VCC to GND. 4 GND Analog Ground. Connect GND to the exposed pad. 5 PGND 6 LX 7 SEC Secondary Current Sensing. Connect SEC to the return of the secondary winding to sense secondary winding current. See Figure 2. 8 DONE Charge-Done Indicator. DONE is an open-drain output that pulls low when EN is high and the circuit has finished charging the output capacitor. 9 EN Enable Input. Drive EN high to turn on the charger, or low to turn it off. 10 UVI Input Undervoltage Detect. Connect a resistor from UVI to the battery to make a resistor-divider with an internal 25k resistor. Input current is reduced when VUVI drops below 1V. Connect UVI to VCC when this feature is not used. -- EP Exposed Pad. Connect the exposed pad to GND and PGND. Power Ground. Connect PGND to the exposed pad. Transformer Primary Connection. Connect LX to the transformer primary as shown in Figure 2. _______________________________________________________________________________________ 5 MAX8622 Typical Operating Characteristics (continued) (VCC = VIN = VEN = 3.5V, circuit of Figure 2, TA = +25C, unless otherwise noted.) MAX8622 Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones Detailed Description The MAX8622 charges photoflash capacitors quickly and efficiently. It employs a transformer flyback DC-DC conversion topology and includes a 0.31 internal power switch. Figure 1 shows the functional diagram. Control Scheme The MAX8622 uses a constant peak and valley current control scheme to precisely control the photoflash capacitor charging current. A resistor at ISET and the transformer turns ratio sets the charge current. Pulling EN high initiates charging. LX turns on and the current in the transformer primary winding rises to a peak current between 0.6A and 1.6A, depending on the ISET resistor (1.6A if ISET is connected to VCC). LX then turns off, and current is delivered to the photoflash capacitor by the transformer secondary and rectifying diode. As secondary current ramps down, it is monitored through the SEC pin. When this current drops to 1.67% (with a 1:15 transformer turns ratio) of the peak current limit, the LX switch turns on and a new charge cycle begins. This cycle repeats itself, adding power to the photoflash capacitor until the target output voltage is reached. Switching frequency is determined by the time required to ramp the primary-side inductance to the LX current limit and the discharge rate of the secondary current. The switching frequency changes as the output capacitor charges to the target output voltage. Once the target output voltage is reached, the MAX8622 automatically refreshes the output every 11s, efficiently maintaining the capacitor charge level with minimum battery drain. The MAX8622 draws only 60A (typ) in automatic refresh mode. Automatic refresh can be overridden by pulling EN low. Secondary Side Sensing Output regulation is accomplished using a resistordivider connected to the anode of the output rectifying diode (see Figure 2). This connection eliminates DC current drain on the output capacitor while still providing direct output sensing for optimum voltage accuracy that is not dependent on transformer turns ratio. The MAX8622 samples FB during the flyback phase (when LX is off). When FB rises above 1.25V, charging stops and DONE pulls low. If EN remains high, autorefresh then occurs every 11s. See the Adjustable Output Voltage section for information on selecting values for the resistor-divider. VIN 1.5V TO 5.5V VCC 2.5V TO 5.5V VCC REF 0.1s T1 LX ISET S QB R Q R6 R5 VCC UVI 20s REF PGND 11s EN SEC R TTL Q S DONE R1 D1 R3 C3 FB R Q S REF GND MAX8622 Figure 1. Functional Diagram 6 _______________________________________________________________________________________ VOUT 300V Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones C2 10F R1 124k T1 1:15 VCC 2.5V TO 5.5V R4 100k ISET UVI C1 1F LX VCC MAX8622 VIN 1.5V TO 5.5V D1 OUTPUT 300V C3 150F R2 124k SEC FB MAX8622 R3 1k DONE PGND EN GND Figure 2. MAX8622 Typical Application Circuit with Default 1.6A Primary Current Limit Table 1. Transformer Design Parameters DC RESISTANCE () TURNS RATIO (SEC/PRI) PRIMARY INDUCTANCE (H) CAPACITANCE (pF) PRI SEC TDK LDT565630T-011 15 6 30 0.11 15 Tokyo Coil TTRN-038S-017-T 15 6.4 11 0.11 24 Tokyo Coil TTRN-SU20S-001-T 15 6.5 4 0.31 44 TRANSFORMER Extending Battery Life with UVI The UVI circuit allows the output to charge as fast as possible without causing the input voltage to drop below the selected voltage level. This allows a camera to be ready to flash in a short time when the battery is fresh, while still charging the photoflash capacitor when the battery is at low capacity by extending charge time and limiting battery drain. The UVI comparator determines if the input source is being pulled low as a result of the input current drawn by photoflash charging or some other process in the camera. When UVI drops below the UVI falling threshold, the LX control latch is reset and the internal MOSFET is immediately turned off. The LX switch remains off until the current in the transformer secondary drops to the valley trip threshold, or for 1s, whichever is longer. The LX switch turns on only if the input is above the UVI rising threshold. This lowers the average charge current. transformer also plays a key role in the noise performance of the circuit. Proper selection, design, and construction of the transformer are crucial to the performance of a photoflash charger. Recommended transformers and their key parameters are listed in Table 1. Transformer Turns Ratio The transformer turns ratio should be high enough so that the transformer's peak primary voltage does not exceed the voltage rating (33V) of the internal MOSFET. The turns ratio is given by: N VOUT(MAX) + VD1 33 - VIN Transformer Design where VD1 is the forward voltage of D1. If the target voltage for the photoflash capacitor is 300V, this implies a turns ratio of greater than 1:10 at a minimum input voltage of 1.8V. A transformer with a turns ratio of 1:15 is typically recommended for applications using the MAX8622. The transformer is a key element in any transformer flyback design. The switching elements in this topology are subject to significantly large voltage and current stresses, depending on the transformer design. The The MAX8622 operates either in discontinuous-conduction mode (DCM) or in continuous-conduction mode (CCM). Generally, CCM operation offers higher efficien- Applications Information Primary Inductance _______________________________________________________________________________________ 7 MAX8622 Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones cy and lower ripple currents for the same output power as compared to DCM operation. The capacitive switching losses in the switch are minimal at the boundary of DCM and CCM operation. The primary inductance for the transformer is therefore estimated based on the assumption that the MAX8622 is operating close to this boundary for highest efficiency and minimum charge time. The MAX8622 has an on-time limit (tON(MAX)) of typically 25s. Assuming the default current limit (ILIMIT) of 1.6A, the maximum value of primary inductance for a 1.8V minimum input and a 1.6A primary current limit is given by: LPRI(MAX) = VIN(MIN) x t ON(MAX) ILIMIT = 1.8 x 25 x 10 -6 = 28H 1.6 The boundary of DCM/CCM operation is determined by monitoring the secondary valley current. The secondary current-sensing circuit in the MAX8622 has a blanking time of about 150ns. This implies a minimum off-time tOFF(MIN) of 250ns for the MAX8622 to have adequate time to sense the secondary valley current. Since the minimum discharge time occurs at the target output voltage V OUT(MAX) , the minimum secondary inductance LSEC(MIN) is given by: L SEC(MIN) = VOUT(MAX) x t OFF(MIN) ILIMIT / N where N is the transformer turns ratio. This in turn implies a minimum primary inductance LPRI(MIN) given by: LPRI(MIN) = VOUT(MAX) x t OFF(MIN) ILIMIT x N = 300 x 250 x 10 -9 47H = N 1.6 x N For a typical turns ratio of 15 (see the Transformer Turns Ratio section), the LPRI(MIN) is calculated to be 3H. Choose a value between L PRI(MIN) and L PRI(MAX) based on other considerations for the leakage inductance and the transformer capacitance. A transformer with a primary inductance of 6H is recommended for most applications. Leakage Inductance A particularly important transformer parameter is leakage inductance. In a practical transformer construction, all windings cannot be equally well-coupled to the core 8 because of physical separation. If the primary inductance is high, the transformer may need multiple windings for the primary. A small amount of energy is stored between the windings and this energy is represented as leakage inductance. If the primary inductance is too small, the primary windings may not cover the width of the core and result in poor coupling to the secondary. This also increases the leakage inductance. Leakage inductance does not participate in the primary to secondary energy transfer. Since the leakage inductance does not find a path for the current built up during the switch on-time, it results in voltage spikes and ringing at the drain of the MAX8622 power switch (LX), when it turns off. The MAX8622 internal switch is designed to be robust to withstand these voltage spikes; however, voltage overshoot should be minimized because it reduces total efficiency. Leakage inductance also delays the transfer of power from input to output causing an increase in charge time. In addition, transformer secondary leakage inductance may couple with the reverse recovery current of the output rectifier diode to cause ringing when the diode turns off. The transformer secondary leakage inductance and the capacitance of the rectifier determine this resonant frequency. There is typically very little loss in the resonant circuit, so this network can generate many cycles of ringing after the spike. The ringing can therefore affect the peak primary current-sense signal used by the MAX8622. The transformer secondary leakage inductance is a function of the primary leakage inductance. Care should be taken during transformer design while using techniques such as sandwiching the secondary between two primary windings to minimize leakage inductance. This can cause high winding-to-winding capacitance, reduce the efficiency of the circuit, and increase the charge time. Transformer Secondary Capacitance The total capacitance of the secondary should be minimized for both efficient and proper operation. Since the secondary of the transformer undergoes large voltage swings, capacitance on the secondary is a significant detriment to efficiency. This capacitance is reflected on the primary as an effective capacitance proportional to the square of the transformer turns ratio. It therefore dominates the resulting capacitance on the primary. _______________________________________________________________________________________ Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones Rectifying Diode The rectifying diode(s) must have sufficient reverse voltage and forward-current ratings. The peak reverse voltage VR(PEAK) seen by the diode(s) is given by: VR(PEAK) = VOUT(MAX) + (N x VIN ) is the same as the secondary peak current ISBC(PEAK). The peak current of the diode ISEC(PEAK) is determined by the peak primary current as: I ISEC(PEAK) = LIMIT N Rectifier capacitance and transformer secondary leakage inductance couple to cause ringing when the diode turns off. The overshoot caused by this ringing may exceed the diode voltage rating and cause damage to the diode. The ringing can also affect the current-sense signal in the MAX8622. The rectifying diode should therefore have very low capacitance; 5pF or less is recommended. The transition from the conduction to the blocking state in the diode takes a finite time, known as the reverse recovery time (t rr ). An ideal diode would have no reverse leakage current at any time. In a real diode, reverse leakage current flows from cathode to anode for a short period of time during reverse recovery to remove the injected carriers before the voltage can be blocked. The reverse recovery time should be as small as possible to reduce losses due to this reverse current. The reverse recovery waveforms also generate noise that may interfere with the current-sense signal. The slope of the waveform for recovery from the peak reverse current to 0A is used to characterize the diode as a soft recovery type if the slope is small, or a hard recovery type if the slope is steep. A soft recovery diode exhibits significantly lower switching noise than a hard recovery type. Snubbers can be used to make the reverse recovery waveform soft, but they also lower efficiency. A diode with a small trr and soft recovery is definitely an advantage. Recommended diodes are listed in Table 2. Table 2. Recommended Diodes PART NUMBER SUPPLIER MAXIMUM REVERSE VOLTAGE (V, EACH) BAV23S (dual) Phillips 250 5 BAW101S (dual) Phillips 300 2 CMPD2004S (dual) Central 240 5 across a wide temperature range. Use of Y5V and Z5U dielectrics is strongly discouraged due to the higher voltage and temperature coefficient of these materials. Adjustable Output Voltage The MAX8622 uses secondary feedback to sense the output voltage (see Figure 2). The output voltage is set by the ratio of a resistor voltage-divider. Choose the lower resistor (R3 in Figure 2), connected from FB to GND, less than 2k. A typical value for R3 is 1k. Larger resistor values combined with parasitic capacitance at FB can slow the rise time of the FB voltage during each cycle. This could prevent the MAX8622 from detecting when the output has reached the desired level. The value for the upper resistor (R1 and R2 in Figure 2) is found from: V RUPPER = R1 + R2 = R 3 OUT - 1 VFB where VFB is 1.25V. Make sure the voltage rating of the resistors is sufficient. It is often necessary to use two resistors in series for the upper resistor to meet the resistor voltage rating. Choosing a Resistor for Lowering Charge Current The peak primary current limit for the MAX8622 is set to the default value of 1.6A by connecting ISET to VCC. This current limit works well for most applications. If a lower current limit is needed, connect a resistor (R6 in Figure 3) from ISET to GND. Select R6 as follows: Capacitor Selection The VCC and VIN decoupling capacitors should be multilayer ceramic type with X5R or X7R dielectric for use CAPACITANCE (pF, EACH) R6 = 1.6A x 75k ILIMIT _______________________________________________________________________________________ 9 MAX8622 Both the leakage inductance and the secondary capacitance of the transformer should be minimized for efficient operation. MAX8622 Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones VIN 1.5V TO 5.5V C2 10F R1 124k T1 R5 25k 1:15 VCC 2.5V TO 5.5V D2 UVI C1 1F R2 124k LX VCC D1 OUTPUT 300V C3 150F SEC FB MAX8622 R4 330k ISET R6 120k DONE EN R3 1k PGND GND Figure 3. MAX8622 Typical Application Circuit with Resistor-Set Primary Current Limit Set by R6 Adjusting Battery Threshold for Lowering Charge Current The UVI circuit allows a camera to be ready to flash in a short time when the battery is fresh, while still allowing flash pictures when the battery is at low capacity by extending the charge time to limit the battery drain. The MAX8622 does this by turning off the internal switch when the battery voltage dips below the set threshold. Set the UVI falling threshold by connecting a resistor (R5 in Figure 3) between UVI and the battery input, which forms a voltage-divider with an internal 25k resistor. Select the UVI resistor value as follows: VIN(MIN) R5 = 25k x - 1 V UVI where VUVI is 1V and VIN(MIN) is the desired minimumoperating battery voltage. When V CC is connected to V IN , the UVI falling threshold must be set to 2.5V or higher. DONE Output DONE is an open-drain output that pulls low when EN is high and the circuit has finished charging the output capacitor. Once the output capacitor is initially charged, DONE remains low until EN or VCC goes low. To use DONE as a logic-level output, connect a pullup resistor (typically 100k) from DONE to the logic sup- 10 ply rail. DONE can also directly drive an LED (connected as shown in Figure 3). When driving an LED, select the series resistor value so the current into DONE is less than 10mA. Note that in the DONE state, the MAX8622 autorefreshes every 11s as long as EN is high. Layout Guidelines The high-voltage operation of this application demands careful attention to board layout. Larger than minimum space between traces in the high-voltage area are recommended. This is essential to meet the breakdown specifications of the board. To minimize the high-frequency noise generated by switching, high dv/dt paths must be made as short as possible. Shortening high dv/dt paths reduces the size of antennas that radiate noise. A high di/dt loop creates noise due to radiated magnetic fields. To reduce high di/dt loop-generated noise, the loop needs to be made as small as possible. Keep the area for the high-voltage end of the secondary as small as possible. Refer to the MAX8622 evaluation kit data sheet for a layout example. Warning: Lethal voltages are present in this circuit. Use caution when working with this circuit. Chip Information TRANSISTOR COUNT: 6062 PROCESS: BiCMOS ______________________________________________________________________________________ Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones 6, 8, &10L, DFN THIN.EPS D2 D A2 PIN 1 ID N 0.35x0.35 b PIN 1 INDEX AREA E [(N/2)-1] x e REF. E2 DETAIL A e k A1 CL CL A L L e e PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm -DRAWING NOT TO SCALE- 21-0137 G 1 2 ______________________________________________________________________________________ 11 MAX8622 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) MAX8622 Fast-Charge-Time Xenon Flash Charger for Digital Still Cameras and Camera Phones Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) COMMON DIMENSIONS MIN. MAX. D 0.70 2.90 0.80 3.10 E A1 2.90 0.00 3.10 0.05 L k 0.20 0.40 0.25 MIN. A2 0.20 REF. SYMBOL A PACKAGE VARIATIONS PKG. CODE N D2 E2 e JEDEC SPEC b [(N/2)-1] x e DOWNBONDS ALLOWED T633-1 6 1.500.10 2.300.10 0.95 BSC MO229 / WEEA 0.400.05 1.90 REF NO T633-2 6 1.500.10 2.300.10 0.95 BSC MO229 / WEEA 0.400.05 1.90 REF NO T833-1 8 1.500.10 2.300.10 0.65 BSC MO229 / WEEC 0.300.05 1.95 REF NO T833-2 8 1.500.10 2.300.10 0.65 BSC MO229 / WEEC 0.300.05 1.95 REF NO T833-3 8 1.500.10 2.300.10 0.65 BSC MO229 / WEEC 0.300.05 1.95 REF YES T1033-1 10 1.500.10 2.300.10 0.50 BSC MO229 / WEED-3 0.250.05 2.00 REF NO T1433-1 14 1.700.10 2.300.10 0.40 BSC ---- 0.200.05 2.40 REF YES T1433-2 14 1.700.10 2.300.10 0.40 BSC ---- 0.200.05 2.40 REF NO PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm -DRAWING NOT TO SCALE- 21-0137 G 2 2 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. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.