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TM
MP1529
Fixed Frequency Step-Up Converter LCD Backlight Plus Flash
The Future of Analog IC Technology
TM
DESCRIPTION
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.
FEATURES
* * * * * * * * * * * * * * * * * 2.7V to 5.5V Input Voltage Range 25V Maximum Step-Up Voltage <1A 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 PDAs Cellular Phones Digital Still Cameras Digital Video Cameras
APPLICATIONS
"MPS" and "The Future of Analog IC Technology" are Trademarks of Monolithic Power Systems, Inc.
TYPICAL APPLICATION
VIN D1
16 IN EN1 EN2 COMP SW OUT 14 12
VOUT
Efficiency vs LED Current
(Backlight Mode, 2 Strings of 3 LEDs) 82 80
EFFICIENCY (%)
EN1 EN2 C4 10nF
1 2 3 4 9 10 11 6
VIN=4.2V VIN=3.6V VIN=2.7V
78 76 74 72
MP1529
SS ISET1 ISET2 ISET3 GND LED1 LED2 LED3 PGND 8 7 5 13, 15
2
4
GND
MP1529_TAC_S01
6 8 10 12 14 16 18 20 LED CURRENT (mA)
MP1529_EC01
MP1529 Rev. 1.0 11/23/2005
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MP1529 - FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH
PACKAGE REFERENCE
PIN 1 ID IN 16 EN1 EN2 COMP SS 1 2 3 4 5 LED3 6 GND 7 8
ABSOLUTE MAXIMUM RATINGS (1)
VIN ................................................. -0.3V to +6V VSW, VOUT, VLED1, VLED2, VLED3 .......... -1V to +40V All Other Pins................................. -0.3V to +6V Junction Temperature...............................125C Lead Temperature ....................................260C Storage Temperature ..............-65C to +150C
TOP VIEW
PGND 15 SW 14 PGND 13 12 11 10 9 OUT ISET3 ISET2 ISET1
Recommended Operating Conditions
(2)
Supply Voltage VIN .......................... 2.7V to 5.5V LED Current (Backlight)............ 30mA Maximum LED Current (Flash) ............... 150mA Maximum Operating Temperature .............-40C to +85C
Thermal Resistance
MP1529_PD01-QFN16
(3)
LED2 LED1
QFN16 (4mm x 4mm) ............. 60 ...... 12... C/W
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.
JA
JC
EXPOSED PAD ON BACKSIDE CONNECT TO PIN 6
Part Number* MP1529DR *
Package QFN16 (4mm x 4mm)
Temperature -40C to +85C
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 = +25C, 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 SW Switch Current Limit Symbol Condition VEN1 = VEN2 = 0V VEN1 = 3V, VEN2 = 0V, BL mode without switching VIN Rising Min Typ 0.5 1.5 2.0 210 28 VOUT = 28V, VEN1 = VEN2 = 0V ILED1,2 = 20mA ILED3 = 40mA ILED3 = 100mA IISET1,2,3 = 20A ILED1,2 = 20mA ILED3 = 100mA VEN1 = VEN2 = 0V VSW = 27V 1.2 1 0.95 1.1 1 1.216 440 480 0.25 1 Max 1 3 2.6 Units A mA V mV V A mA/A mA/A mA/A V mV mV A A
MP1529 Rev. 1.0 11/23/2005
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MP1529 - FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH
ELECTRICAL CHARACTERISTICS (continued)
VIN = 3.6V, TA = +25C, 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 IC = 10A 1.0 Min Typ 200 1.2 95 1.4 1.4 0.3 CSS = 16nF CSS = 16nF CSS = 16nF 1 10 160 10 50 Max Units A/V MHz % V V ms 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 1.2M. 2 EN2 Enable Input. See Table 1 for PWM serial interface usage. EN2 has an internal pull-down of 1.2M. 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
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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.
Efficiency vs. LED Current Backlight Mode, 1 String of 3 LEDs
VIN=4.2V
EFFICIENCY (%)
85
85
Efficiency vs. LED Current Backlight Mode, 1 String of 4 LEDs
VIN=3.6V
EFFICIENCY (%)
85
Efficiency vs. LED Current Backlight Mode, 1 String of 6 LEDs
EFFICIENCY (%)
80
VIN=2.7V
80 VIN=2.7V 75 VIN=4.2V
80 VIN=3.6V 75 VIN=4.2V
75
VIN=2.7V
70
VIN=3.6V 0 5 15 ILED_BL(mA) 10 20 25
70
70
65
65
0
5
15 ILED_BL (mA)
10
20
25
65
0
5
10 15 ILED_BL (mA)
20
25
MP1529-TPC01
MP1529-TPC02
MP1529-TPC03
Efficiency vs. VIN Flash Mode
95 35 30
EFFICIENCY (%)
LED Current Setting Backlight Mode
LED Current vs. VIN
120 100 80
ILED (mA)
90
ILED_BL (mA)
3 LEDs 85 4 LEDs
25 20 15 10 5
Flash Mode
60 40 20 Backlight Mode 0 Preview Mode
80
75 2.5
3.0
3.5 VIN (V)
4.0
4.5
0
0
100 200 300 400 500 600 700
MP1529-TPC05
2.5
3.0
3.5 VIN (V)
4.0
4.5
MP1529-TPC04
MP1529-TPC06
Current Matching LED1 vs. LED2
22 20
ILED_BL (mA)
ILED_BL vs. PWM Dimming Duty Cycle
25 LED1
ILED_BL (mA)
20 15 10 5 0
18 16 14 12
LED2
2.5
3.0
3.5 VIN (V)
4.0
4.5
20
40 60 80 DUTY CYCLE (%)
100
MP1529-TPC07
MP1529-TPC08
MP1529 Rev. 1.0 11/23/2005
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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 Steady State Operation Flash Mode
VSW 5V/div. VOUT AC Coupled 20mV/div. IL 0.2A/div.
VSW 5V/div. VOUT AC Coupled 20mV/div. IL 0.2A/div.
VSW 10V/div. VOUT AC Coupled 20mV/div. IL 0.5A/div.
400ns/div.
MP1529-TPC09
400ns/div.
MP1529-TPC10
400ns/div.
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
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MP1529 - FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH
BLOCK DIAGRAM
SW VIN PWM & OSC OUT
COMP
---+ VREF SOFT-START/ PWM TIMER
LED1 LED2 LED3
SS
EN1 EN2
LOGIC GND
ISET1 ISET2 ISET3
MP1529_F01_DB01
CURRENT PROGRAM
Figure 1--Functional Block Diagram
MP1529 Rev. 1.0 11/23/2005
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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 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.
MP1529 Rev. 1.0 11/23/2005
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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) H (PWM) L EN2 L L H H Strings 1 & 2: LCD Backlight LEDs Off On (PWM) On (PWM) Off String 3: Flash LEDs Off Off Preview current 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 k by the equations:
950 x VSET RS1 = ILED _ BL
Use an input capacitor value of 4.7F 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 1F to 4.7F 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 x C2 x f SW
RS2 =
RS3 =
1100 x VSET ILED _ PV
1000 x 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.
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.
MP1529 Rev. 1.0 11/23/2005
www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2005 MPS. All Rights Reserved.
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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 x fSW x I VOUT x ILED _ FL VIN x
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 1F 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.
IIN(MAX ) =
I = (30% - 50%)IIN(MAX )
Where I is the peak-to-peak inductor ripple current and is the efficiency at flash mode. A 4.7H or 10H inductor is recommended for most cell phone applications. 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
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MP1529 - FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH
TYPICAL APPLICATION CIRCUITS
VIN D1
16 IN EN1 EN2 COMP SS SW OUT 14 12
VOUT
EN1 EN2
1 2 3 4 9 10
MP1529
LED1 LED2 LED3 PGND 8 7 5 13, 15
ISET1 ISET2 ISET3 GND
C4 10nF GND
11 6
MP1529_F02_S01
Figure 2-- Driving 1 Backlight String (20mA per WLED) and 1 Flash String (40mA Preview, 100mAFlash)
VIN D1
16 IN EN1 EN2 COMP SS SW OUT 14 12
VOUT
EN1 EN2
1 2 3 4 9 10
MP1529
LED1 LED2 LED3 PGND 8 7 5
ISET1 ISET2 ISET3 GND
(A) (A) (B)
C4 10nF GND
11 6
13, 15
(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
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MP1529 - FIXED FREQUENCY STEP-UP CONVERTER LCD BACKLIGHT PLUS FLASH
TYPICAL APPLICATION CIRCUITS (continued)
VIN D1
16 IN EN1 EN2 COMP SS SW OUT 14 12
VOUT
EN1 EN2
1 2 3 4 9 10
MP1529
LED1 LED2 LED3 PGND 8 7 5 13, 15
ISET1 ISET2 ISET3 GND
C4 10nF GND
11 6
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)
13
2.35 (0.093) 2.45 (0.097)
16
Pin 1 Identification
1
3.950 (0.156) 4.050 (0.159)
QFN 16L (4 X 4mm)
0.40 (0.0158) 0.50 (0.0197)
0.650 BSC
R0.030Max.
9 4
0.28 (0.011) 0.38 (0.015)
8
5
Top View
2.280 (0.898) Ref.
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. (c) 2005 MPS. All Rights Reserved.
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