Specifications

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Rev. 1.0 January 2012

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AOZ1978

Dual Channel High Voltage

LED Driver I

General Description

The AOZ1978 is a dual-channel high-efficiency LED

driver controller for high voltage LED backlighting

applications. It is designed to independently drive

two high-brightness LED light bars in LED TV

applications. The AOZ1978 can support a wide

range of input and output voltages. The input bias

voltage range of AOZ1978 is from 8V to 18V.

The AOZ1978 has multiple features to protect the

regulator under fault conditions. A control pin can

disable an external switch to disconnect the LEDs

current path from the output in PWM dimming or

under catastrophic failure conditions. Cycle-by-cycle

current protection limits the peak inductor current.

Thermal shutdown provides another level of

protection. An output flag to indicate the fault

condition if output of any channel is shorted to

ground.

Low feedback voltage (500mV) helps to reduce

power loss.

The AOZ1978 is available in a standard SO-20

package and operates over the temperature range of

-40C to +85C.

Features

 8V to 18V input bias voltage

 180⁰ Out of phase channel switching provides

input ripple current cancellation

 18V driving capability at GATE pins

 Disconnect control pin for PWM dimming or fault

conditions

 Flag to indicate output short or fault condition

 500mV feedback regulation

 External reference input and Analog Dimming

capability

 8 bit PWM dimming resolution

 Cycle-by-cycle current limit

 Output over-voltage protection

 LED short and open protection

 Thermal shutdown protection

 SO-20 package

Applications

 LCD TV LED backlight

Typical Application

Summary of content (17 pages)

PAGE 1
AOZ1978 Dual Channel High Voltage LED Driver IC General Description Features The AOZ1978 is a dual-channel high-efficiency LED driver controller for high voltage LED backlighting applications. It is designed to independently drive two high-brightness LED light bars in LED TV applications. The AOZ1978 can support a wide range of input and output voltages. The input bias voltage range of AOZ1978 is from 8V to 18V.   The AOZ1978 has multiple features to protect the regulator under fault conditions.
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AOZ1978 Ordering Information Part Number Temperature Range Package Environmental AOZ1978AI -40°C to +85°C SOIC-20 Green AOS Green Products use reduced levels of Halogens, and are also RoHS compliant. Please visit www.aosmd.com/web/quality/rohs_compliant.jsp for additional information.
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AOZ1978 Pin Description Part Number Pin Name 1 2 VIN DPWM1 3 GATE1 4 5 GND COMP1 6 OVP1 7 DBRT1 8 9 10 CS1 FB1 ISET 11 SCP 12 13 14 FB2 CS2 DBRT2 15 OVP2 16 COMP2 17 18 GND GATE2 19 DPWM2 20 FLAG Rev. 1.0 January 2012 Pin Function Input Supply Pin. Fault and Dimming PWM Control Output for Channel 1. DPWM1 = High for LED connect. DPWM1 = Low for LED disconnect. Connect to the gate of external NMOS switch. External Boost NMOS Gate Controller Pin for Channel 1.
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AOZ1978 Pin Functions Pin1: VIN This is the input supply for the controller IC; it is also the voltage drive for the Gates and DPWM drivers. If the input power of the boost converter is less than 18V, VIN can be connected directly to the boost supply voltage. If the boost supply voltage is higher than 18V, a separate supply rail between 8V and 18V is required for the VIN pin. It is recommended that an RC filter should be added between VIN and Boost supply if they are connected directly.
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AOZ1978 Pin 12: FB2 This is the feedback input for boost controller for CH2. This pin should connect to a resistor that senses the LED current. The FB2 voltage will be regulated to Pin 10 (ISET) voltage. If the voltage at FB2 pin exceeds 1V due to a fault condition CH2 will shut down for 40ms and will try again every 40ms until the fault condition is removed. Note that this is the only fault condition that will not assert a FLAG. Pin 13: CS2 This is the input for peak current sense for CH2.
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AOZ1978 Functional Block Rev. 1.0 January 2012 www.aosmd.
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AOZ1978 Absolute Maximum Ratings Recommended Operating Ratings Exceeding the Absolute Maximum Ratings may damage the device. This device is not guaranteed to operate beyond the Recommended Operating Ratings. Parameter VIN to GND GATE1, DPWM1, GATE2, DPWM2 to GND COMP1, OVP1, DBRT1, CS1, FB1, ISET COMP2, OVP2, DBRT2, CS2, FB2, SCP, FLAG to GND Storage Temperature (TS) ESD Rating(1) Parameter Supply Voltage (VVIN) Ambient Temperature (TA) Package Thermal Resistance SOIC-20 (JA) Rating -0.
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AOZ1978 Electrical Characteristics (continued) Symbol Protection VCS VSCP VSCP_HYS OVP_THRSHLD FLAG_TO TTHERMAL_SD TTHERMAL_HYS Parameter Conditions Min. Typ. Max Units CS Threshold Voltage SCP Threshold Voltage SCP Hysteresis OVP Threshold Voltage FLAG Time OUT Thermal Shutdown Threshold Thermal Shutdown Hysteresis CS1 or CS2 360 0.864 440 1.056 OVP1 or OVP2 0.9 400 0.
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AOZ1978 DBRT1 or Typical Performance Characteristics Switching Waveforms and Input Current: PVIN = 100V, VLED = 200V, ILED = 125mA/CH Rev. 1.0 January 2012 www.aosmd.
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AOZ1978 Typical Performance Characteristics (continued) Rev. 1.0 January 2012 www.aosmd.
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AOZ1978 Detailed Description The AOZ1978 is a dual channel boost DC/DC controller designed to power a series of LEDs by regulating the current into an LED string. The LED current information is provided to the system through the sense resistor RFB at the bottom of each LED string, between FB and GND pins. Protection Features Over-Current Protection at Boost Switch The current limit is a function of RCS resistor value at CS pin and the internal set threshold of 0.4V limit.
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AOZ1978 Application Information Inductor Selection Inductor choice will be affected by many parameters, like duty cycle based on input/output setting, switching frequency, full scale LED current level, and mode of operations. Boost controller can operate under discontinuous mode, continuous mode, or critical conduction mode. For high voltage boost LED driver applications, it is recommended to use critical conduction mode for best stability and good efficiency.
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AOZ1978 For typical application, we recommend to set the voltage at CS to approximately 0.3V when inductor current reaches the peak. To accommodate load, line and inductor tolerances variation, 30% margin is included in the above calculation. RRTN Ground return current sense resistor, this resistor is optional and if desired can be used to add an extra layer of protection against output shorts or any other fault condition that causes excessive return current.
PAGE 14
AOZ1978 PCB Layout Consideration Correct layout practices are essential for a working design that will meet expectations. It is recommended to use two-layer board for the design. However, a single layer board would be sufficient if basic layout rules are followed. In any SMPS layout, external components should be grouped into Power or IC control. From typical application circuit, there are two GND symbols. The striped one is for Power GND and the solid one is for Signal/Control GND.
PAGE 15
AOZ1978 Package Dimensions, SOIC-20L RECOMMENDED LAND PATTERN Symbols Min. Nom. Max. Symbols Min. Nom. Max. A 2.35 2.52 2.65 A 0.093 0.099 0.104 A1 0.10 0.20 0.30 A1 0.004 0.008 0.012 A2 2.05 2.35 2.55 A2 0.081 0.093 0.100 b 0.35 — 0.49 b 0.014 — 0.019 c 0.23 — 0.32 c 0.009 — 0.013 D 12.60 12.70 12.80 D 0.496 0.500 0.504 E 7.40 10.00 7.50 10.20 7.60 10.60 E E1 0.291 0.394 0.295 0.402 0.299 0.417 E1 e 1.27 BSC 0.80 1.27 e L1 1.
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AOZ1978 Plastic Tube and Plug, SOIC-20L Cannot read text ANTISTATIC Test Ht. 2.54 max Printing 7.874 R 0.254 Max (Typ) CNRT CNRT CNRT 2.413–2.718 CNRT 4.699 CNRT CNRT CNRT CNRT CNRT 4.902 CNRT 4.902 3.683 CNRT All Sides 14.732 CNRT Vendor Coder 0701–0005XXX Option Rev. NOTES: 1. All dimensions are in millimeters. 2. Tube material, clear rigid PVC. 3. Print color, white. 4. Character thickness, 0.254 millimeters. 5. “ANTISTATIC” print to be placed at center of tube’s length and width.
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AOZ1978 Part Marking AOZ1978AI (SOIC-20) Z1978AI FX YW LT Part Number Code Assembly Lot Code Fab & Assembly Location Year & Week Code This datasheet contains preliminary data; supplementary data may be published at a later date. Alpha and Omega Semiconductor reserves the right to make changes at any time without notice. LIFE SUPPORT POLICY ALPHA & OMEGA SEMICONDUCTOR PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS. As used herein: 1.