PAM99700AC

PART OBSOLETE - USE AL9910A PAM99700 UNIVERSAL HIGH BRIGHTNESS LED DRIVER Description Pin Assignments OBSOLETE – PART DISCONTINUED The PAM99700 is an open-loop current-mode control LED-driver integrated circuit (IC). The PAM99700 can be programmed to operate in either a constant frequency or constant off-time mode. The device includes a 12V to 500V regulator, which allows the device to work from a wide range of input voltages without the requirement for an external low-voltage supply. The PAM99700 includes a pulse-width modulation (PWM) dimming input that can accept an external control signal with a duty ratio of 0% to 100% and a frequency of up to a few kilohertz. The device also includes a 0mV to 250mV linear dimming input, which can be used for linear dimming of the LED current. The PAM99700 is ideally suited for buck LED drivers. Because the PAM99700 operates in open-loop current-mode control, the controller achieves good output current regulation without the requirement for any loop compensation. PWM dimming response is limited only by the rate of rise and fall of the inductor current, which enables very fast rise and fall times. The PAM99700 requires only three external components (apart from the power stage) to produce a controlled LED current making the device an ideal solution for low-cost LED drivers. Features Applications  Switch-Mode Controller for Single-Switch LED Drivers      Open-Loop Peak-Current Controller Constant Frequency or Constant Off-Time Operation Linear and PWM Dimming Capability Requires Few External Components for Operation Application From a Few mA to More than 1A Output      PAM99700 Document number: DS36455 Rev. 2 - 4 DC/DC or AC/DC LED Driver Applications RGB Backlighting LED Driver Back Lighting of Flat Panel Displays General Purpose Constant Current Source Signage and Decorative LED Lighting 1 of 12 www.diodes.com May 2018 © Diodes Incorporated PAM99700 OBSOLETE – PART DISCONTINUED Typical Applications Circuit Pin Descriptions Pin Name VIN Pin Number SOP-8 SOP-16 1 1 Function This pin is the input of a 12V to 500V regulator. CS 2 4 GND 3 5 This pin is the current-sense pin used to sense the FET current by means of an external sense resistor. When this pin exceeds the lower of either the internal 250mV or the voltage at the LD pin, the gate output goes low. Ground return for all internal circuitry. This pin must be electrically connected to the ground of the power train. GATE 4 8 This pin is the output gate driver for an external N-Channel power MOSFET. PWMD 5 9 VDD 6 12 LD 7 13 RT 8 14 NC — 2, 3, 6, 7, 10, 11, 15, 16 PAM99700 Document number: DS36455 Rev. 2 - 4 This is the PWM dimming input of the IC. When this pin is pulled to GND, the gate driver is turned off. When the pin is pulled high, the gate driver operates normally. This is the power supply pin for all internal circuits. It must be bypassed with a low ESR capacitor to GND (approximately 10μF). This pin is the linear dimming input and sets the current sense threshold as long as the voltage at the pin is less than 250mV (typ). This pin sets the oscillator frequency. When a resistor is connected between RT and GND, the PAM99700 operates in constant frequency mode. When the resistor is connected between RT and GATE, the IC operates in constant off-time mode. Not connected. 2 of 12 www.diodes.com May 2018 © Diodes Incorporated PAM99700 OBSOLETE – PART DISCONTINUED Functional Block Diagram Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.) These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods can affect device reliability. All voltages are with respect to ground. Parameter Maximum Junction Temperature Storage Temperature Soldering Temperature Rating 150 -65 to +150 300, 5sec Unit °C Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.) Parameter Supply Voltage Ambient Temperature Range Junction Temperature Range Rating 12 to 500 -40 to +85 -40 to +125 Unit V °C °C Thermal Information Parameter Thermal Resistance (Junction to Ambient) PAM99700 Document number: DS36455 Rev. 2 - 4 Package SOP-8 SOP-16 Symbol θJA 3 of 12 www.diodes.com Max 115 110 Unit °C/W May 2018 © Diodes Incorporated PAM99700 Electrical Characteristics (@TA = +25°C, unless otherwise specified.) Parameter OBSOLETE – PART DISCONTINUED Input Voltage Range Symbol VINDC Test Conditions DC Input Voltage Shutdown Mode Supply Current IINSD Pin PWMD to GND VDD Min Typ Max 12 — 500 Units V — 0.1 — mA VIN > 20V 6 10 — V VCS,TH — — 250 — mV Current Sense Blanking Interval TBLANK — — 250 — Ns Gate-Sourcing Current ISOURCE VGATE = 0V 0.2 — — A ISINK VGATE = VDD 0.2 — — A Gate-Output Rise Time tRISE CGATE = 1nF — 30 50 ns Gate-Output Fall Time tTALL CGATE = 1nF — 30 50 ns RT = 510kΩ 37 41 49 RT = 226kΩ 74 92 110 — — Internally Regulated Voltage Current Sense Pull-In Threshold Voltage Gate-Sinking Current Oscillator Frequency fOSC EN Threshold High VEH VIN = 12V to 500V 2.4 EN Threshold Low VEL OTP OTH VIN = 12V to 500V — — — — 1.0 V — — 160 50 — — °C °C Overtemperature Protection (OTP) OTP Hysteresis PAM99700 Document number: DS36455 Rev. 2 - 4 4 of 12 www.diodes.com kHz V May 2018 © Diodes Incorporated PAM99700 Typical Performance Characteristics OBSOLETE – PART DISCONTINUED (@TA = +25°C, VIN = 60V, 1WLED, RT = 510KΩ, L = 5.2mH, unless otherwise specified.) PAM99700 Document number: DS36455 Rev. 2 - 4 5 of 12 www.diodes.com May 2018 © Diodes Incorporated PAM99700 Typical Performance Characteristics (continued) OBSOLETE – PART DISCONTINUED (@TA = +25°C, VIN = 110VAC, 1WLED, RT = 510KΩ, L = 5.2mH, RCS = 0.68Ω, unless otherwise specified.) PAM99700 Document number: DS36455 Rev. 2 - 4 6 of 12 www.diodes.com May 2018 © Diodes Incorporated PAM99700 OBSOLETE – PART DISCONTINUED Application Information The PAM99700 is optimized to drive buck LED drivers using open-loop peak current-mode control. This method of control enables fairly accurate LED current control without the requirement for high-side current sensing or the design of any closed-loop controllers. The IC uses very few external components and enables both linear and PWM dimming of the LED current. A resistor connected to the RT pin programs the frequency of operation (or the off time). The oscillator produces pulses at regular intervals. These pulses set the SR flip- flop in the PAM99700, which causes the gate driver to turn on. The same pulses also start the blanking timer, which inhibits the reset input of the SR flip-flop and prevents false turnoffs due to the turn-on spike. When the FET turns on, the current through the inductor starts ramping up. This current flows through the external sense resistor RCS and produces a ramp voltage at the CS pin. The comparators are constantly comparing the CS pin voltage to both the voltage at the LD pin and the internal 250mV. Once the blanking timer is complete, the output of these comparators is allowed to reset the flip-flop. When the output of either one of the two comparators goes high, the flip-flop is reset, and the gate output goes low. The gate goes low until the SR flip-flop is set by the oscillator. Assuming a 30% ripple in the inductor, the current sense resistor RCS can be set using the following equation. Rcs = 0.25V (or VLD)/1.15 * ILED(A) Constant-frequency peak current-mode control has an inherent disadvantage—at duty cycles greater than 0.5, the control scheme goes into subharmonic oscillations. To prevent this, an artificial slope is typically added to the current-sense waveform. This slope compensation scheme affects the accuracy of the LED current in the present form. However, a constant off-time peak-current control scheme does not have this problem and can easily operate at duty cycles greater then 0.5 and also gives inherent input voltage rejection, which makes the LED current almost insensitive to input-voltage variations. However, this control scheme leads to variable frequency operation, and the frequency range depends greatly on the input- and output-voltage variation. PAM99700 makes it easy to switch between the two modes of operation by changing one connection (see oscillator section). Input Voltage Regulator The PAM99700 can be powered directly from its VIN pin and can work from 12V to 500V DC at its VIN pin. When a voltage is applied at the VIN pin, the PAM99700 maintains a constant 12V at the VDD pin. This voltage is used to power the IC and any external resistor dividers required to control the IC. The VDD pin must be bypassed by a low-ESR capacitor to provide a low-impedance path for the high-frequency current of the output-gate driver. The PAM99700 can also operate by supplying a voltage at the VDD pin greater than the internally regulated voltage. This turns off the internal linear regulator of the IC, and the PAM99700 operates directly off the voltage supplied at the VDD pin. Note this external voltage at the VDD pin must not exceed 15V. Although the VIN pin of the PAM99700 is rated up to 500V, the actual maximum voltage that can be applied is limited by the power dissipation in the IC. For example, if an 8-pin (junction -to-ambient thermal resistance RθJ-A = 115°C/W) PAM99700 draws about IIN = 2mA from the VIN pin and has a maximum allowable temperature rise of the junction temperature limited to about ΔT = 100°C, the maximum voltage at the VIN pin would be: VIN(MAX )   T RJ A  1 IIN 100C 1  115C / W 2mA  435V In these cases, to operate the PAM99700 from higher input voltages, a Zener diode can be added in series with the VIN pin to divert some of the power loss from the PAM99700 to the Zener diode. In the above example, using a 100V zener diode allows the circuit to easily work up to 500V. The input current drawn from the VIN pin is a sum of the 1.0mA current drawn by the internal circuit and the current drawn by the gate driver, which depends on the switching frequency and the gate charge of the external FET. IIN  350A  QG * f s In the above equation, fS is the switching frequency, and QG is the gate charge of the external FET, which can be obtained from the datasheet of the FET. PAM99700 Document number: DS36455 Rev. 2 - 4 7 of 12 www.diodes.com May 2018 © Diodes Incorporated PAM99700 Application Information (continued) OBSOLETE – PART DISCONTINUED Current Sense The current-sense input of the PAM99700 goes to the non-inverting inputs of two comparators. The inverting terminal of one comparator is tied to an internal 250mV reference, whereas the inverting terminal of the other comparator is connected to the LD pin. The outputs of both of these comparators are fed into an OR gate, and the output of the OR gate is fed into the reset pin of the flip-flop. Thus, the comparator that has the lowest voltage at the inverting terminal determines when the GATE output is turned off. The outputs of the comparators also include a 150ns to 280ns blanking time that prevents spurious turnoffs of the external FET due to the turnon spike normally present in peak current-mode control. In rare cases, this internal blanking might not be enough to filter out the turn-on spike. In these cases, an external RC filter must be added between the external sense resistor (RCS) and the CS pin. Note the comparators are fast with a typical 80ns response time. Hence these comparators are more susceptible to be triggered by noise than the comparators of the PAM99700. A proper layout minimizing external inductances prevents false triggering of these comparators. Oscillator The oscillator in thePAM99700 is controlled by a single resistor connected at the RT pin. The equation governing the oscillator frequency is as follows. F 21380 (kHz) RT(k)  5.5 If the resistor is connected between RT and GND, PAM99700 operates in a constant-frequency mode. The above equation determines the time period. If the resistor is connected between RT and GATE, the PAM99700 operates in a constant off-time mode. The following equation determines the off time. TOFF  RT(k)  44.1 (µS) 21.1 GATE Output The gate output of the PAM99700 drives the external FET. It is recommended that the gate charge of the external FET be