TM MP1529 Fixed Frequency Step-Up Converter LCD Backlight Plus Flash The Future of Analog IC Technology TM DESCRIPTION FEATURES The MP1529 is a step-up converter plus 3 current sources for driving two 6-LED backlight strings to 30mA and a 4-LED flash string to 150mA from a single Lithium-Ion battery. • • • • • • • The step-up converter generates an output voltage as high as 25V from a 2.7V to 5.5V input source. Three current sources drive in three modes. In backlight mode two strings of 6 LEDs are lit with up to 30mA of current. In the backlight plus preview mode the 4 flash LEDs are lit with the preview current. In flash mode the flash LEDs are lit with up to 150mA of current and the two backlight strings are turned off. There are three pins to independently set the backlight, preview and flash current. The MP1529 includes built-in open lamp over voltage protection, cycle-by-cycle current limit, over temperature shutdown, input under voltage control and integrated soft-start. The MP1529 is available in a tiny 16-pin 4mm x 4mm package. • • • • • • 2.7V to 5.5V Input Voltage Range 25V Maximum Step-Up Voltage <1µA Shutdown Mode 1.2MHz Fixed Frequency Operation LCD Backlight to 30mA, Flash to 150mA Cycle-By-Cycle Current Limit Independent Backlight, Preview and Flash Current Adjustment Special PWM Dimming Over Voltage Protection Under Voltage Lockout Integrated Soft-Start Thermal Shutdown Tiny 4mm x 4mm QFN Package APPLICATIONS • • • • PDAs Cellular Phones Digital Still Cameras Digital Video Cameras “MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION VOUT VIN D1 EN1 1 EN2 2 3 C4 10nF 4 9 10 11 6 IN SW OUT (Backlight Mode, 2 Strings of 3 LEDs) 14 82 12 EN1 VIN=4.2V 80 EN2 EFFICIENCY (%) 16 Efficiency vs LED Current COMP MP1529 SS ISET1 LED1 ISET2 LED2 ISET3 LED3 GND PGND 8 7 VIN=3.6V 78 VIN=2.7V 76 74 5 72 13, 15 GND 2 4 6 8 10 12 14 16 18 20 LED CURRENT (mA) MP1529_EC01 MP1529_TAC_S01 MP1529 Rev. 1.0 11/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 1 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH ABSOLUTE MAXIMUM RATINGS (1) PACKAGE REFERENCE IN PGND SW PGND 16 15 14 13 EN1 1 12 OUT EN2 2 11 ISET3 COMP 3 10 ISET2 SS 4 9 ISET1 5 6 LED3 GND 7 MP1529DR * Recommended Operating Conditions Package QFN16 (4mm x 4mm) (2) Supply Voltage VIN .......................... 2.7V to 5.5V LED Current (Backlight)............ 30mA Maximum LED Current (Flash) ............... 150mA Maximum Operating Temperature .............–40°C to +85°C Thermal Resistance 8 (3) θJA θJC QFN16 (4mm x 4mm) ............. 60 ...... 12... °C/W LED2 LED1 EXPOSED PAD ON BACKSIDE CONNECT TO PIN 6 Part Number* VIN ................................................. –0.3V to +6V VSW, VOUT, VLED1, VLED2, VLED3 .......... –1V to +40V All Other Pins................................. –0.3V to +6V Junction Temperature...............................125°C Lead Temperature ....................................260°C Storage Temperature ..............–65°C to +150°C TOP VIEW PIN 1 ID MP1529_PD01-QFN16 Temperature Notes: 1) Exceeding these ratings may damage the device. 2) The device is not guaranteed to function outside of its operating conditions. 3) Measured on approximately 1” square of 1 oz copper. –40°C to +85°C For Tape & Reel, add suffix –Z (eg. MP1529DR–Z) For Lead Free, add suffix –LF (eg. MP1529DR–LF–Z) ELECTRICAL CHARACTERISTICS VIN = 3.6V, TA = +25°C, unless otherwise noted. Parameter Shutdown Supply Current Supply Current Under Voltage Lockout Under Voltage Lockout Hysteresis OUT Over Voltage Threshold OUT Leakage Current ISET1 Backlight Current Gain ISET2 Preview Current Gain ISET3 Flash Current Gain ISET1, ISET2 and ISET3 Voltage LED1 and LED2 Voltage LED3 Voltage SW Switch On Resistance SW Switch Leakage Current Symbol Condition VEN1 = VEN2 = 0V VEN1 = 3V, VEN2 = 0V, BL mode without switching VIN Rising Min Typ 0.5 Max 1 Units µA 1.5 3 mA 2.6 V mV V 1 µA 2.0 210 28 VOUT = 28V, VEN1 = VEN2 = 0V ILED1,2 = 20mA ILED3 = 40mA ILED3 = 100mA IISET1,2,3 = 20µA ILED1,2 = 20mA ILED3 = 100mA 0.95 1.1 1 1.216 440 480 0.25 VEN1 = VEN2 = 0V VSW = 27V SW Switch Current Limit MP1529 Rev. 1.0 11/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. mA/µA mA/µA mA/µA V mV mV Ω 1 1.2 µA A 2 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH ELECTRICAL CHARACTERISTICS (continued) VIN = 3.6V, TA = +25°C, unless otherwise noted. Parameter Current Sense to COMP Transconductance Oscillation Frequency SW Maximum Duty Cycle EN1, EN2 High Voltage EN1, EN2 Low Voltage EN1, EN2 Turn-Off Delay to Shutdown (4) EN1 PWM Frequency (4) Soft-Start Period (4) Thermal Shutdown Symbol Condition Min ∆IC = ±10µA Typ Max 200 1.0 1.2 95 µA/V 1.4 1.4 0.3 CSS = 16nF CSS = 16nF CSS = 16nF 10 1 MHz % V V ms 50 10 160 Units KHz ms °C Note: 4) The soft-start timer and the PWM timer are the same timer with the same timing. PIN FUNCTIONS Pin # Name Description 1 EN1 Enable Input. See Table 1 for PWM serial interface usage. EN1 has an internal pull-down of 1.2MΩ. 2 EN2 Enable Input. See Table 1 for PWM serial interface usage. EN2 has an internal pull-down of 1.2MΩ. Control Loop Compensation Node. COMP is the output of the internal transconductance amplifier. 3 COMP Connect a series resistor-capacitor network between COMP and GND to compensate the control loop. 4 SS Soft-Start Capacitor Pin. Doubles as the PWM timer. Number 3 LED String Current Control Input. Connect the bottom (Cathode) of the Number 3 LED 5 LED3 string to LED3. This string is the flash string. 6 GND Analog Ground. (Connect the Exposed Pad to Pin 6) Number 2 LED String Current Control Input. Connect the bottom (Cathode) of the Number 2 LED 7 LED2 string to LED2. This string is the backlight string. Number 1 LED String Current Control Input. Connect the bottom (Cathode) of the Number 1 LED 8 LED1 string to LED1. This string is the backlight string. Current Control Input. Connect a resistor between ISET1 and GND to set the backlight LED string 9 ISET1 current up to 30mA. Current Control Input. Connect a resistor between ISET2 and GND to set the flash LED string 10 ISET2 preview current up to 150mA. Current Control Input. Connect a resistor between ISET3 and GND to set the flash LED string current 11 ISET3 up to 150mA. Output Voltage Sensing Input. When the OUT pin voltage exceeds the overvoltage threshold, the 12 OUT MP1529 automatically shuts down to prevent internal damage. Connect OUT to the output of the step-up converter. Switch Output. SW is the drain of the internal N-Channel MOSFET switch. Connect the power 14 SW inductor between SW and the input source, and connect the output rectifier between SW and the output to form the step-up converter. 16 IN Input Supply Pin. Must be locally bypassed. 13,15 PGND Power Ground. MP1529 Rev. 1.0 11/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 3 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH TYPICAL PERFORMANCE CHARACTERISTICS Circuit of Figure 2, VIN = 3.6V, 3 LEDs on LED1, 3 LEDs on LED2, 3 LEDs on LED3, ILED_BL = 20mA, ILED_PV = 40mA, ILED_FL = 100mA, unless otherwise noted. 80 VIN=2.7V 75 70 65 VIN=3.6V 0 5 10 15 ILED_BL(mA) 20 85 VIN=3.6V 80 VIN=2.7V 75 0 5 MP1529-TPC01 15 ILED_BL (mA) 20 90 4 LEDs 3.0 120 30 100 4.0 20 15 0 4.5 10 15 ILED_BL (mA) 20 25 Flash Mode 60 40 Preview Mode Backlight Mode 0 0 100 200 300 400 500 600 700 2.5 3.0 MP1529-TPC05 Current Matching LED1 vs. LED2 3.5 VIN (V) 4.0 4.5 MP1529-TPC06 ILED_BL vs. PWM Dimming Duty Cycle 22 25 LED1 18 20 ILED_BL (mA) 20 ILED_BL (mA) 5 20 MP1529-TPC04 LED2 16 14 12 0 80 10 3.5 VIN (V) 70 35 5 75 2.5 VIN=4.2V VIN=2.7V LED Current vs. VIN ILED (mA) ILED_BL (mA) 85 VIN=3.6V 75 MP1529-TPC03 25 3 LEDs 80 65 25 LED Current Setting Backlight Mode 95 EFFICIENCY (%) 10 85 Efficiency vs. LED Current Backlight Mode, 1 String of 6 LEDs MP1529-TPC02 Efficiency vs. VIN Flash Mode 80 VIN=4.2V 70 65 25 Efficiency vs. LED Current Backlight Mode, 1 String of 4 LEDs EFFICIENCY (%) VIN=4.2V EFFICIENCY (%) EFFICIENCY (%) 85 Efficiency vs. LED Current Backlight Mode, 1 String of 3 LEDs 15 10 5 2.5 3.0 3.5 VIN (V) 4.0 4.5 MP1529-TPC07 MP1529 Rev. 1.0 11/23/2005 0 20 40 60 80 DUTY CYCLE (%) 100 MP1529-TPC08 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 4 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH TYPICAL PERFORMANCE CHARACTERISTICS (continued) Circuit of Figure 2, VIN = 3.6V, 3 LEDs on LED1, 3 LEDs on LED2, 3 LEDs on LED3, ILED_BL = 20mA, ILED_PV = 40mA, ILED_FL = 100mA, unless otherwise noted. Steady State Operation Backlight Mode Steady State Operation Backlight plus Preview Mode VSW 5V/div. VSW 5V/div. VSW 10V/div. VOUT AC Coupled 20mV/div. VOUT AC Coupled 20mV/div. IL 0.2A/div. IL 0.2A/div. VOUT AC Coupled 20mV/div. IL 0.5A/div. 400ns/div. Steady State Operation Flash Mode 400ns/div. MP1529-TPC09 400ns/div. MP1529-TPC10 MP1529-TPC11 Start-up into Open LEDs VOUT 10V/div. VSW 10V/div. IL 0.5A/div. 1ms/div. MP1529-TPC12 MP1529 Rev. 1.0 11/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 5 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH BLOCK DIAGRAM OUT SW VIN PWM & OSC COMP LED1 -- LED2 -- LED3 -+ VREF SS EN1 EN2 SOFT-START/ PWM TIMER LOGIC GND ISET1 ISET2 CURRENT PROGRAM ISET3 MP1529_F01_DB01 Figure 1—Functional Block Diagram MP1529 Rev. 1.0 11/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 6 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH OPERATION The MP1529 white LED driver performs both dual string backlight and single string flash functions for portable applications. The features include pulse width modulated (PWM) dimming of the backlight LEDs to 30mA, preview with the same dimming capability on the backlight strings and flash only mode to 150mA. Preview allows the flash LEDs to illuminate the camera scene such that the correct exposure setting can be set. The 4mm x 4mm package fits in most applications. Startup and Shutdown EN1 and EN2 are the enables for the backlight strings and the flash string, respectively. When the inputs are low, the part is either in shutdown mode or on the way to shutdown. We will describe the shutdown behavior later. Upon enabling the MP1529, the SS pin ramps its voltage to provide soft-start protection against supply inrush current. Typically the ramps last 1ms to 10ms depending on capacitor selection. EN1 lights up the LED1 and LED2 strings for the backlight application. The current setting is 950 times the current in ISET1 for each of the strings. EN1 and EN2 together turn on the backlight strings and the preview mode in the flash string. The preview mode current is 1100 times the current in ISET2. The final setting depends on the PWM timer, which is the soft-start timer after the soft-start has completed and has the same timing. PWM Brightness Adjust The PWM timer provides continuous operation of the flash string and other internal functions when the PWM low interval of EN1 is shorter than the PWM timing. Should the EN1 low interval be longer than the timer interval, the EN1 pin will assume a steady state low value. One example: when the PWM is too slow on EN1, it will result in the part turning off or entering flash mode depending on the state of EN2. EN2 uniquely affects this mode by resetting the PWM timer each time EN2 changes state. This allows a user to make a transition from preview to flash faster by MP1529 Rev. 1.0 11/23/2005 passing through the off state. The change in EN2 resets the PWM and causes the flash to react immediately. The slower path is to stop the PWM and make a low transition on EN1 in the preview mode and to wait for the PWM timer to clear for flash mode. The time for this method is that of the PWM timer, which is the same as the SS timer. Other features of the 1529 are constant frequency operation with cycle-by-cycle current limit as well as over voltage and over temperature protection. Open String Protection There is also open string protection through the over voltage protection that prevents the 1529 from trying to start an open string indefinitely. The over voltage signal forces the part to forget about open LED strings and to resume regulation on the remaining strings. Initially, any open string will force the part to pump to its maximum voltage. At this point, the part will mark off strings that it simply cannot light properly. Once the mark-off operation completes, the remaining LED strings force the output voltage back into tight regulation. The string with the highest voltage drop is the ruling string during output regulation. Once a string is marked off, its current regulation cannot force the loop regulation to set the output voltage. Marked-off LED strings will continue to seek current regulation and may come into current regulation if their connections return or improve. However, the ability to light the string properly will vary due to the lack of output voltage control. The part will maintain mark-off information until the part shuts down or another LED string opens to force an over voltage condition. Each time the over voltage condition is triggered, the part marks off strings according to their ability to reach current regulation. The MP1529 will always try to light at least one string and will ignore the case wherein all the strings are marked off. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 7 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH Table 1—Enable Operation Table (5, 6, 7) Mode Off Backlight Backlight plus Preview Flash EN1 L H (PWM) EN2 L L Strings 1 & 2: LCD Backlight LEDs Off On (PWM) String 3: Flash LEDs Off Off H (PWM) H On (PWM) Preview current L H Off Flash current Notes: 5) Backlight and Backlight plus Preview may use PWM for backlight brightness control. Only strings 1 & 2 will respond to high speed PWM. String 3 will remain continuously on or off depending on the mode. 6) Any combination of backlight string may be used. 1 or 2 or 1 & 2 will regulate properly. The part uses over voltage detection to determine which strings are available to light. The remaining strings are then used for regulation. The part will not remain in an open loop mode if there is at least one string of LEDs to light. 7) Changing from backlight plus preview to flash will have a delay equal to the soft-start timer due to the PWM filtering necessary for preview. Switching the part to off mode then to flash will cancel the timer. This will take a few microseconds instead of the 10 milliseconds typically associated with the timer being active. APPLICATION INFORMATION Setting the LED currents Resistors RS1, RS2 and RS3 set the backlight LED string (LED1 and LED2) current, the flash LED string (LED3) preview current, and the flash LED string current, respectively. Determine each current setting resistor in kΩ by the equations: 950 × VSET RS1 = ILED _ BL RS2 = 1100 × VSET ILED _ PV RS3 = 1000 × VSET ILED _ FL Where VSET is the internal reference voltage, typically 1.216V. ILED_BL, ILED_PV and ILED_FL are the backlight LED string current, the flash LED string preview current, and the flash LED string flash current in mA, respectively. Selecting the Input Capacitor An input capacitor is required to supply the AC ripple current to the inductor, while limiting noise at the input source. This capacitor must have low ESR, so ceramic is the best choice. MP1529 Rev. 1.0 11/23/2005 Use an input capacitor value of 4.7µF or greater. This capacitor must be placed physically close to the IN pin. Since it reduces the voltage ripple seen at IN, it also reduces the amount of EMI passed back along that line to the other circuitry. Selecting the Output Capacitor A single 1µF to 4.7µF ceramic capacitor usually provides sufficient output capacitance for most applications. The impedance of the ceramic capacitor at the switching frequency is dominated by the capacitance, and so the output voltage ripple is mostly independent of the ESR. The output voltage ripple VRIPPLE is calculated as: VRIPPLE = ILED (VO UT − VIN ) VO UT × C2 × f SW Where VOUT is the output voltage, VIN is the input voltage, ILED is the total LED current, C2 is the capacitance of the output capacitor, and fSW is the 1.2MHz switching frequency. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 8 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH Selecting the Inductor The inductor is required to force the output voltage higher while being driven by the lower input voltage. Choose an inductor that does not saturate at the SW current limit. A good rule for determining the inductance is to allow the peak-to-peak ripple current to be approximately 30%-50% of the maximum input current. The maximum input current usually occurs in flash mode. Make sure that the peak inductor current is below 75% of the typical current limit to prevent loss of regulation due to the current limit variation. Calculate the required inductance value L using the equations: L= VIN (VOUT - VIN ) VOUT × fSW × ∆I IIN(MAX ) = VOUT × ILED _ FL VIN × η ∆I = (30% − 50%)IIN(MAX ) Where ∆I is the peak-to-peak inductor ripple current and η is the efficiency at flash mode. A 4.7µH or 10µH inductor is recommended for most cell phone applications. Selecting the Compensation Capacitor The compensation capacitor needs to be determined so that the control loop is slow enough to allow for stable and smooth mode transition. A 1µF ceramic capacitor is recommended for most cell phone applications. Selecting the Soft-Start Capacitor The soft-start capacitor sets both the soft-start timer and the PWM timer. A 10nF to 22nF capacitor is recommended for most applications. Layout Considerations High frequency switching regulators require very careful layout for stable operation and low noise. All components must be placed as close to the IC as possible. Keep the path between the SW pin, output diode, output capacitor and GND pin extremely short for minimal noise and ringing. The input capacitor must be placed close to the IN pin for best decoupling. All current setting resistors must be kept close to the corresponding ISET pin to prevent noise injection for accurate LED current setting. The ground return of the input and output capacitors should be tied close to the GND pin. See the MP1529 demo board layout for reference. Selecting the Diode The output rectifier diode supplies current to the inductor when the internal MOSFET is off. To reduce losses due to diode forward voltage and recovery time, use a Schottky diode. Choose a diode whose maximum reverse voltage rating is greater than the maximum output voltage. For output voltage less than 20V, it is recommended to choose the MBR0520 for most applications. MP1529 Rev. 1.0 11/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 9 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH TYPICAL APPLICATION CIRCUITS VIN VOUT D1 16 EN1 1 EN2 2 3 4 9 10 C4 10nF 11 6 IN SW OUT EN1 14 12 EN2 COMP MP1529 SS ISET1 LED1 ISET2 LED2 ISET3 LED3 GND PGND 8 7 5 13, 15 GND MP1529_F02_S01 Figure 2— Driving 1 Backlight String (20mA per WLED) and 1 Flash String (40mA Preview, 100mAFlash) VOUT VIN D1 16 EN1 1 EN2 2 3 4 9 10 C4 10nF 11 6 IN SW OUT EN1 14 12 EN2 COMP SS MP1529 ISET1 LED1 ISET2 LED2 ISET3 LED3 GND PGND 8 (A) 7 (A) 5 (B) 13, 15 GND (A) LCD BACKLIGHT LEDS (B) FLASH LEDS MP1529_F03_S01 Figure 3—Driving 2 x 3 Backlight Strings (20mA per WLED) and 1 Flash String (40mA Preview, 100mA Flash) MP1529 Rev. 1.0 11/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 10 TM MP1529 – FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH TYPICAL APPLICATION CIRCUITS (continued) VIN VOUT D1 16 EN1 1 EN2 2 3 4 9 10 11 C4 10nF 6 IN 14 SW 12 OUT EN1 EN2 COMP SS MP1529 ISET1 LED1 ISET2 LED2 ISET3 LED3 GND PGND 8 7 5 13, 15 GND MP1529_F04_S01 Figure 4—Driving 2 x 6 Backlight Strings (20mA per WLED) and 1 Flash String (40mA Preview, 100mAFlash) PACKAGE INFORMATION QFN16 (4mm x 4mm) Pin 1 Dot By marking 3.950 (0.156) 4.050 (0.159) 0.550 (0.217) 0.650 (0.256) 3.950 (0.156) 4.050 (0.159) QFN 16L (4 X 4mm) Pin 1 Identification 2.35 (0.093) 2.45 (0.097) 16 13 1 0.40 (0.0158) 0.50 (0.0197) 4 0.28 (0.011) 0.38 (0.015) 0.650 BSC R0.030Max. 9 8 5 2.280 (0.898) Ref. Top View Exposed Pad (Analog Ground) Btm View Side View 0.850 ( 0.0335) 0.950 (0.0374) 0.000-0.025 0.178 (0.007) 0.228 (0.009) NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MP1529 Rev. 1.0 11/23/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 11