LT3741

LT3724 High Voltage, Current Mode Switching Regulator Controller FEATURES n n n n n n n n n n n n n DESCRIPTION The LT®3724 is a DC/DC controller used for medium power, low part count, low cost, high efficiency supplies. It offers a wide 4V-60V input range (7.5V minimum startup voltage) and can implement step-down, step-up, inverting and SEPIC topologies. The LT3724 includes Burst Mode operation, which reduces quiescent current below 100µA and maintains high efficiency at light loads. An internal high voltage bias regulator allows for simple biasing and can be back driven to increase efficiency. Additional features include fixed frequency current mode control for fast line and load transient response; a gate driver capable of driving large N-channel MOSFETs; a precision undervoltage lockout function; 10µA shutdown current; short-circuit protection; and a programmable soft-start function that directly controls output voltage slew rates at startup which limits inrush current, minimizes overshoot and facilitates supply sequencing. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Burst Mode is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5731694, 6498466, 6611131. Wide Input Range: 4V to 60V Output Voltages up to 36V (Step-Down) Burst Mode® Operation: 9V VBURST_EN = 0V, VFB = 1.35V VSHDN = 0V CONDITIONS l l l ELECTRICAL CHARACTERISTICS MIN 4 7.5 3.65 TYP MAX 60 UNITS V V V mV µA µA µA 3724fd 3.8 670 20 20 10 3.95 IVIN 15 2 LT3724 ELECTRICAL CHARACTERISTICS SYMBOL VBOOST PARAMETER Operating Voltage Range Operating Voltage Range (Note 5) UVLO Threshold (Rising) UVLO Threshold Hysteresis BOOST Supply Current (Note 6) BOOST Burst Mode Current BOOST Shutdown Current Operating Voltage Range (Note 5) Output Voltage UVLO Threshold (Rising) UVLO Threshold Hysteresis VCC Supply Current (Note 6) VCC Burst Mode Current VCC Shutdown Current Short-Circuit Current Error Amp Reference Voltage Feedback Input Current Enable Threshold (Rising) Threshold Hysteresis Common Mode Range Current Limit Sense Voltage Input Current (ISENSE+ + ISENSE–) Operating Frequency MP Grade VFB(SS) ISS gm AV VC IVC VTG tTG tTG(OFF) tTG(ON) ISW Soft-Start Disable Voltage Soft-Start Disable Hysteresis Soft-Start Capacitor Control Current Error Amp Transconductance Error Amp DC Voltage Gain Error Amp Output Range Error Amp Sink/Source Current Gate Drive Output On Voltage (Note 7) CLOAD = 3300pF Gate Drive Output Off Voltage CLOAD = 3300pF Gate Drive Rise/Fall Time Minimum Switch Off Time Minimum Switch On Time SW Pin Sink Current VSW = 2V l l l l l l l The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 20V, VCC = BOOST = BURST_EN = 10V, SHDN = 2V, SENSE – = SENSE+ = 10V, SGND = PGND = SW = 0V, unless otherwise noted. CONDITIONS VBOOST - VSW VBOOST - VSW VBOOST - VSW VBURST_EN = 0V VSHDN = 0V Over Full Line and Load Range l l l l MIN TYP MAX 75 20 UNITS V V V mV mA µA µA 5 400 1.4 0.1 0.1 8 6.25 500 1.7 80 20 –55 1.231 25 1.3 0 140 1.35 120 150 400 2 –150 190 175 165 200 200 1.185 300 2 275 340 62 1.2 ±30 9.8 0.1 60 350 300 300 IBOOST VCC 20 8.3 V V V mV mA µA µA mA V V nA V mV V mV µA µA µA IVCC l VBURST_EN = 0V VSHDN = 0V l 2.1 – 30 1.224 1.215 VFB IFB VSHDN VSENSE ISENSE fSW Measured at VFB Pin l 1.238 1.245 1.4 36 175 VSENSE+ – VSENSE– VSENSE(CM) = 0V VSENSE(CM) = 2.5V VSENSE(CM) > 4V 210 220 225 kHz kHz kHz V mV µA VFB Rising 400 µmhos dB V µA V V ns ns Zero Current to Current Limit 10% to 90% or 90% to 10%, CLOAD = 3300pF 500 ns mA 3724fd 3 LT3724 ELECTRICAL CHARACTERISTICS Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3724 includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 3: The LT3724E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the – 40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3724I is guaranteed over the full –40°C to 125°C operating junction temperature range. The LT3724MP is 100% tested and guaranteed over the –55°C to 125°C operating junction temperature range. Note 4: VIN voltages below the start-up threshold (7.5V) are only supported when the VCC is externally driven above 6.5V. Note 5: Operating range is dictated by MOSFET absolute maximum VGS. Note 6: Supply current specification does not include switch drive currents. Actual supply currents will be higher. Note 7: DC measurement of gate drive output “ON” voltage is typically 8.6V. Internal dynamic bootstrap operation yields typical gate “ON” voltages of 9.8V during standard switching operation. Standard operation gate “ON” voltage is not tested but guaranteed by design. Note 8: The –1V absolute maximum on the SW pin is a transient condition. It is guaranteed by design and not subject to test. TYPICAL PERFORMANCE CHARACTERISTICS Shutdown Threshold (Rising) vs Temperature 1.38 SHUTDOWN THRESHOLD, FALLING (V) SHUTDOWN THRESHOLD, RISING (V) 1.37 1.36 1.35 1.34 1.33 1.32 –50 –25 1.26 1.25 1.24 1.23 1.22 1.21 1.20 –50 –25 VCC (V) Shutdown Threshold (Falling) vs Temperature 8.2 8.1 8.0 7.9 7.8 7.7 7.6 0 25 50 75 TEMPERATURE (°C) 100 125 VCC vs Temperature ICC = 20mA 0 25 50 75 TEMPERATURE (°C) 100 125 7.5 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 3724 G01 3724 G02 3724 G03 VCC vs ICC(LOAD) 8.2 8.1 8.0 VCC (V) VCC (V) 7.9 7.8 7.7 7.6 7.5 0 15 20 25 30 35 TA = 25°C 8 7 6 5 4 3 9 VCC vs VIN ICC = 20mA TA = 25°C ICC CURRENT LIMIT (mA) 70 ICC Current Limit vs Temperature 60 50 40 30 5 10 4 5 6 7 8 VIN (V) 9 10 11 12 20 –50 –25 ICC (LOAD) (mA) 3724 G04 0 25 50 75 TEMPERATURE (°C) 100 125 3724 G05 3724 G06 3724fd 4 LT3724 TYPICAL PERFORMANCE CHARACTERISTICS VCC UVLO Threshold (Rising) vs Temperature 6.5 VCC UVLO THRESHOLD, RISING (V) 25 ICC vs VCC (SHDN = 0V) TA = 25°C ERROR AMP TRANSCONDUCTANCE (µMhos) Error Amp Transconductance vs Temperature 350 345 340 335 330 325 320 –50 –25 6.4 20 15 6.2 ICC (µA) 6.3 10 5 6.1 6.0 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 0 0 2 4 6 8 10 12 14 16 18 20 VCC (V) 3724 G08 50 25 75 0 TEMPERATURE (°C) 100 125 3724 G07 3724 G09 400 300 I(SENSE+ + SENSE–) (µA) 200 100 0 I(SENSE+ + SENSE–) vs VSENSE (CM) TA = 25°C OPERATING FREQUENCY (kHz) Operating Frequency vs Temperature 230 220 210 200 190 180 170 –50 –25 1.234 1.233 ERROR AMP REFERENCE (V) 1.232 1.231 1.230 1.229 1.228 50 25 75 0 TEMPERATURE (°C) 100 125 Error Amp Reference vs Temperature –100 –200 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VSENSE (CM) (V) 3724 G10 1.227 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 3724 G11 3724 G12 Maximum Current Sense Threshold vs Temperature 160 CURRENT SENSE THRESHOLD (mV) VIN UVLO THRESHOLD, RISING (V) 158 156 154 152 150 148 146 144 142 140 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 4.54 4.52 4.50 4.48 4.46 4.44 4.42 VIN UVLO Threshold (Rising) vs Temperature 3.86 VIN UVLO THRESHOLD, FALLING (V) 50 25 75 0 TEMPERATURE (°C) 100 125 VIN UVLO Threshold (Falling) vs Temperature 3.84 3.82 3.80 3.78 4.40 –50 –25 3.76 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 3724 G13 3724 G14 3724 G15 3724fd 5 LT3724 PIN FUNCTIONS VIN (Pin 1): The VIN pin is the main supply pin and should be decoupled to SGND with a low ESR capacitor located close to the pin. NC (Pin 2): No Connection. SHDN (Pin 3): The SHDN pin has a precision IC enable threshold of 1.35V (rising) with 120mV of hysteresis. It is used to implement an undervoltage lockout (UVLO) circuit. See Application Information section for implementing a UVLO function. When the SHDN pin is pulled below a transistor VBE (0.7V), a low current shutdown mode is entered, all internal circuitry is disabled and the VIN supply current is reduced to approximately 10µA. Typical pin input bias current is