Evaluates: MAX20070/MAX20070B MAX20070 Evaluation Kit General Description Features The MAX20070 evaluation kit (EV kit) demonstrates 2.7V to 5.5V Input Range for TFT Power Section the MAX20070 IC, which is a highly integrated power 4.5V to 16V Input Range for LED Driver Section supply plus LED backlight driver for automotive TFT-LCD 1MHz Boost and Inverted Buck-Boost Switching applications. The EV kit is a fully assembled and tested Frequency on TFT Power Section surface-mount PCB that provides a complete power- TFT Section Output Voltages management solution for small-size automotive displays. The EV kit demonstrates one buck-boost converter, one +6.5V Output at 100mA (Step-Up Switching boost converter, two gate-voltage controllers, and a boost Regulator) converter that powers a dual-string LED driver. -6.5V Output at 100mA (Inverting Buck-Boost Switching Regulator) The DC-DC converter portion of the EV kit operates +16V Output at 3mA (Positive-Charge Pump) from a 2.7V to 5.5V DC supply voltage. The step-up -7V Output at 3mA (Negative-Charge Pump) switching regulator (POS) is configured for a 6.5V or 15V output that provides 100mA. The inverting buck-boost HB LED String Output Currents Configurable for converter (NEG) generates a negative output that tracks 80mA or 160mA the positive output and provides 100mA. The gate-driver Demonstrates Cycle-by-Cycle Current-Limit and power supplies consist of regulated charge pumps that Thermal-Shutdown Features on Boost LED Driver generate +16V (GVDD) and -7V (GVEE) and can deliver Demonstrates Adaptive Voltage Optimization on LED up to 3mA each. It is also possible to completely turn off Driver Section the inverting buck-boost regulator by changing the value of the R15 resistor to 140k. Proven PCB Layout and Thermal Design The LED driver section demonstrates a step-up DC-DC Fully Assembled and Tested preregulator followed by two channels of linear current sinks. The step-up preregulator switches at 1MHz and operates as a current-mode-controlled regulator capable of providing up to 300mA for the linear circuits. Each channel is capable of operating up to 38V and provides up to 160mA. The channels are configurable for 80mA or 160mA HB LED output current. Ordering Information appears at end of data sheet. The LED driver portion of the EV kit operates from a DC supply voltage of 4.5V up to the HB LED string-forward voltage. The EV kit can withstand a 40V load-dump condi- tion. The EV kit also demonstrates the ICs features, such as adaptive voltage optimization, overvoltage protection (OVP), cycle-by-cycle current limit, thermal shutdown, and digital PWM dimming operation using a digital PWM input signal to control the brightness of the HB LEDs. The EV kit is shipped with the MAX20070, but can also be used to evaluate the MAX20070B with IC replacement of U1. 19-7549 Rev 1 9/15Evaluates: MAX20070/MAX20070B MAX20070 Evaluation Kit 15) Measure the HB LED current using the current probe Quick Start and verify all channels. Required Equipment Detailed Description of Hardware MAX20070 EV kit The MAX20070 EV kit LED driver section demon- 2.7V to 5.5V DC supply strates the MAX20070 HB LED driver with an integrated 4V to 18V DC supply step-up DC-DC preregulator followed by two channels of Voltmeter linear current sinks. The preregulator switches at 1MHz and operates as a current-mode-controlled regulator, Two series-connected HB LED strings rated to no providing up to 320mA for the linear circuit while less than 160mA providing OVP. Cycle-by-cycle current limit is set by Current probe to measure the HB LED current resistors R5 and R7, while resistors R2, R4, and R16 set the OVP voltage to 41.6V. The preregulator power section Procedure consists of inductor L2, power-sense resistors R5 and R7, The EV kit is fully assembled and tested. Follow the steps and switching diode D1. below to verify board operation. Caution: Do not turn on The EV kit circuit operates from a DC supply voltage of the power supply until all connections are completed. 4.5V up to the HB LED forward-string voltage. The circuit 1) Verify that a shunt is installed on jumpers JP2, JP3, handles load-dump conditions up to 40V. and JP5. Each of the two linear channels (OUT1 and OUT2) is 2) Verify that jumpers JP1 and JP4 are open. 3) Connect the positive terminal of the (2.7V to 5.5V) capable of operating up to 40V and sinks up to 160mA per channel. Each of the two channels linear current sinks power supply to the TFT POWER INPUT PCB pad. Connect the negative terminal of the same are configurable for 160mA or 80mA, or can be disabled power supply to the PGND PCB pad close to the independently by shorting the respective OUT channel TFT POWER INPUT PCB pad. to ground before power-up with the LED string connected 4) Turn on the power supply. to the corresponding OUT channel removed. Resistors 5) Verify that the step-up switching regulator output R6, R8, and jumper JP1 configure the linear current (V ) to GND is +6.5V. setting for the ICs ISET pin, which sets the HB LED string POS 6) Verify that the step-up switching regulator output current. (V ) to GND is -6.5V. NEG The EV kit features PCB pads to facilitate connecting HB 7) Verify that the positive charge-pump supply (V ) DGVDD LED strings for evaluation. The OUT PCB pads provide is approximately +16V. connections for connecting each HB LED strings anode 8) Verify that the negative charge-pump supply to the DC-DC preregulator output. The OUT1 and OUT2 (V ) is approximately -7V. DGVEE PCB pads provide connections for connecting each HB 9) Connect the positive of the (4.0V to 16V) power LED strings cathode to the respective linear channels supply to the BATTERY INPUT PCB pad and the current sink. Capacitors C16 and C32 are included on the power supplys ground to the LGND PCB pad next design to prevent oscillations and provide stability when to the BATTERY INPUT PCB pad. using long, untwisted HB LED connecting cables during 10) Connect the digital voltmeter across the OUT1 and lab evaluation. These capacitors are not required on a LGND PCB pads. The LGND PCB pad is close to the typical HB LED design. OUT PCB pad. A DIM IN PCB pad is provided for using a digital PWM 11) Connect each HB LED string as follows: signal to control the brightness of the HB LEDs. Channel 1: Connect an HB LED string anode to the OUT PCB pad and the cathode to the OUT1 PCB pad. Enable Input (EN) Channel 2: Connect an HB LED string anode to the The ICs source-driver and gate-driver outputs (V , POS OUT PCB pad and the cathode to the OUT2 PCB pad. V , V , and V ) are controlled by driving NEG DGVDD DGVEE 12) Clip the current probe across the channel 1 HB LED+ the EN pin. The LED driver section is also enabled by wire to measure the HB LED current. the EN input. When EN is left open, all the outputs are 13) Turn on the power supply and set it to 10V. disabled. When EN is connected to a 2.1V logic-high (or 14) Measure the voltage from the OUT1OUT2 PCB greater) level, all the outputs are enabled. pads to GND and verify that the lowest voltage is approximately 0.75V. Maxim Integrated 2 www.maximintegrated.com