a8504 Allegro MicroSystems, Inc., a8504 Datasheet
a8504
Available stocks
Related parts for a8504
a8504 Summary of contents
Page 1
... LED channel can sink 45 mA, and channels can be paralleled for higher currents. LED current can be controlled with external PWM duty cycle. The A8504 is available pin × QFN/MLP package that is only 0.75 mm nominal in height. Applications include: ▪ Thin notebook displays ▪ ...
Page 2
... A8504 WLED/RGB Backlight Driver for Medium Size LCDs Selection Guide Part Number A8504EECTR × QFN/MLP *Contact Allegro for additional packing options Device package is lead (Pb) free, with 100% matte tin leadframe plating. Absolute Maximum Ratings Characteristic SW and OVP Pins LED1 through LED8 Pins ...
Page 3
... A8504 WLED/RGB Backlight Driver for Medium Size LCDs ±10 VIN COMP C C Reference and Soft Start SKIP FSET 100 kΩ R FSET AGND GND PWM Generator SEL1 SEL2 SEL3 PWM 100 kΩ ISET R ISET Functional Block Diagram V BAT ...
Page 4
... A8504 ELECTRICAL CHARACTERISTICS, valid at T Characteristics Input Voltage Range Undervoltage Lockout Threshold UVLO Hysteresis Window Supply Current Error Amplifier Error Amplifier Open Loop Gain Error Amplifier Unity Gain Bandwidth Error Amplifier Transconductance Error Amplifier Output Sink Current Error Amplifier Output Source Current ...
Page 5
... A8504 WLED/RGB Backlight Driver for Medium Size LCDs ELECTRICAL CHARACTERISTICS (continued), valid at T otherwise noted Characteristics LED Current Sinks LEDx Regulation Voltage Current Gain SET LEDx Voltage on ISET Pin I Allowable Current Range SET LEDx Accuracy LEDx Matching LEDx Switch Leakage Current ...
Page 6
... A8504 WLED/RGB Backlight Driver for Medium Size LCDs V 100 Duty Cycle (%) Duty Cycle (%) Duty Cycle (%) Duty Cycle (%) Performance Characteristics Efficiency with PWM dimming: PLED/PBAT ...
Page 7
... A8504 WLED/RGB Backlight Driver for Medium Size LCDs 50% Duty Cycle PWM OUT OUT t Symbol Parameter Units/Division C1 V PWM OUT C4 I OUT t time Performance Characteristics Turn-On with PWM Signal 100 Hz BAT PWM 8S8P configuration per channel ...
Page 8
... A8504 The A8504 is a multioutput WLED driver for medium display backlighting. The A8504 works with 4.2 to 5.5 V input supply, and it has an integrated boost converter to boost battery voltage per LED string. An inductor can be connected to a separate power supply from with the A8504 BAT IC powered from source ...
Page 9
... PWM signal on the PWM pin On/off Control (PWM) with an External PWM Signal on the When the PWM pin is pulled high, the A8504 turns on PWM Pin. and all enabled LEDx pins sink 100% current. When the PWM pin is pulled low, the IC shuts down with the LEDx pins disabled ...
Page 10
... LEDs. If any enabled LED string opens, voltage on the corre- sponding LEDx pin goes to zero. The boost loop operates in open loop till the OVP level is reached. The A8504 identifies the open LED string when overvoltage on the OVP pin is detected. This string is then removed from the boost controlling loop. The boost ...
Page 11
... A Use a 100 Hz PWM signal on the PWM pin. The Dimming A8504 can work with wide range of PWM frequencies, taking about 6 μs typical (10 μs maximum) to turn on. This delay may have a noticeable effect at high PWM frequencies combined with low duty cycles. For example, at 100 Hz and 10% duty cycle, the PWM on-period is 1 ms. In that period, a delay of 6 μ ...
Page 12
... Select the compensation capacitor CC (connect between the COMP pin and ground. Typically, use a 0.1 to 0.47 μF 1/2 = 0.48 A. capacitor for stability. High Output Current Operation LED strings can be paralleled for higher current. The A8504 × ∆V , (11) can sink through each sink. These outputs can be SW ...
Page 13
... F V BAT ±10 ROVP VIN SW SW OVP PWM GND AGND SKIP PGND A8504 COMP SEL3 FSET SEL2 SEL1 ISET LED2 LED1 LED3 LED5 LED7 LGND LED8 LED6 LED4 ISET RISETP RISET Q1 1.0 10.0 Dimming Level (%) = 100 Hz ...
Page 14
... LED7 LED6 LED5 LGND LED4 LED3 LED2 All ESD capacitors across LED arrays are 0.1 μF 10 μH OUT C COUT BAT ROVP 2.2 μ OVP PGND A8504 V IN SEL3 SEL2 SEL1 LED1 LED4 LED3 LED2 V OUT COUT GND AGND PGND V SEL3 IN SEL2 ...
Page 15
... In the composite view, the red line superimposed represents the current loop during switch on-time (return through the A8504 device and the PCB ground plane). The green line represents the current loop during off-time. Both of these loops should be designed short as practicable. ...
Page 16
... A8504 WLED/RGB Backlight Driver for Medium Size LCDs Figure 15. A8504 typical PCB layout top signal layer (left) and bottom ground plane layer (right) Recommended Components Table (for application shown in figure 1) Component Capacitor Capacitor Capacitor Diode IC Inductor Resistor Resistor Resistor Figure 14. A8504 typical PCB layout silkscreen layer. ...
Page 17
... A8504 WLED/RGB Backlight Driver for Medium Size LCDs Terminal List Table Number Name 1 PGND Power ground pin. Reduces boost switching frequency in case of light load to improve frequency. Normally, this pin should be low; when 2 SKIP high divided COMP Compensation pin; connect external compensation network for boost converter. ...
Page 18
... A8504 WLED/RGB Backlight Driver for Medium Size LCDs Top View D 27X 0.08 C 0.20 0.40 0. Bottom View Copyright ©2007, Allegro MicroSystems, Inc. The products described here are manufactured under one or more U.S. patents or U.S. patents pending. Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec tions as may be required to per- mit improvements in the per for mance, reliability, or manufacturability of its products ...