TX4138

TX4138 4A, 60V, 200KHz Step-Down Converter FEATURES DESCRIPTION  Wide 4.5V to 60V Operating Input Range The TX4138 is a monolithic step-down switch mode converter. It achieves 4A continuous output current over a wide input supply range with excellent load and line regulation.  Output Adjustable from 0.8V to 40V The maximum peak current can be programmed by sensing current through an accurate sense resistor.  32mΩ Internal Power MOSFET Switch Fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. The TX4138 requires a minimum number of readily available standard external components. The TX4138 is available in 8-pin ESOIC8 packages.  84.5% Efficiency at Vin=60V，Vout=5V@2A  Standby Current 400uA  Power Save Mode at light load  Programmable maximum peak current  93% Efficiency at Vin=60V，Vout=12V@2A  Fixed 200KHz Frequency  Thermal Shutdown  Cycle-by-Cycle Over Current Protection  Available in 8-Pin ESOIC8 Packages Maximum output current and input voltage： APPLICATIONS  Balance Bike  Ebike  USB Power Supplies TYPICAL APPLICATION 3 C1A 100µF 100V C1B VIN BS 8 R3 5.1Ω C3 100nF 2 R4 0.1µF 20mΩ 100V 6 ILIM SW TX4138 5V/3A 1 D1 SS510 L1 33µΗ C2 C4 12pF EN POK GND 7 4 FB 5 www.xdssemi.com R1 300K 1% 470µF 16V R2 57.1K 1% TX4138_V1.1 第 1 页 TX4138 ORDERING INFORMATION Supply Voltage VIN ,VILIM ............................................................. 62V VSW .............................................................................-0.3V to VIN + 0.3V VBST............................................................................................. VSW + 6.0V VPOK ................................................................................................. 0V to 45V All Other Pins .....................................-0.3V to +6.5V Junction Temperature ..................................... 150°C Lead Temperature ........................................... 260°C Storage Temperature ...................... -65°C to +150°C TX4138 PART NUMBER TEMPERATURE RANGE PACKAGE ABSOLUTE MAXIMUM RATINGS (1) -40°C to 85°C ESOIC8 PIN CONFIGURATION (2) Recommended Operating Conditions SW 1 ILIM 2 VIN 3 GND 4 ILIM (9) 8 BS 7 POK 6 EN 5 FB Supply Voltage VIN..........................................................4.5V to 60V O Voltage VOUT ..................................................................0.8V to 40V Operating Temperature ..................... -40°C to +85°C Thermal Resistance (3) θJA θJC ESOIC8 .................................... 45 ......... 15 ......°C/W Notes: 1) Exceeding these ratings may damage the device. 2) The device is not guaranteed to function outside of its operating conditions. 3) Measured on approximately 42x45mm^2 of 1 oz copper. PIN No. PIN NAME PIN DESCRIPTION 1 2、9 SW ILIM 3 VIN 4 Gnd 5 FB 6 EN 7 POK Power good signal. When FB is less than 90% of 0.8V, PGOOD is low. It is an open-drain output. Use a high value pull-up resistor externally to pull it up to system power supply or its output as next chip enable signal. connected to Gnd or floating when don’t use this function. 8 BS Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect a 100nF ceramic cap and 10ohm resistor between this pin and SW. Switch Output. Connect this pin to the switching end of the inductor. programmable maximum peak current pin by sensing current through an accurate sense resistor between this pin and VIN. Supply Voltage. The TX4138 operates from a +4.5V to +60V unregulated input.CIN is needed to prevent large voltage spikes from appearing at the input. Put CIN as close to the IC as possible. It is the drain of the internal power device and power supply for the whole chip. Ground. This pin is the voltage reference for the regulated output voltage. For this reason care must be taken in its layout. This node should be placed outside of the D1 to CIN ground path to prevent switching current spikes from inducing voltage noise into the part. Feedback. An external resistor divider from the output to GND, tapped to the FB pin sets the output voltage. To prevent current limit run away during a short circuit fault condition the frequency-fold-back comparator lowers the oscillator frequency when the FB voltage is below 250mV. Enable pin. Connect to low off the chip,Floating is enable www.xdssemi.com TX4138_V1.1 第 2 页 TX4138 TX413 ELECTRICAL CHARACTERISTICS VIN = 12V, TA = +25°C, unless otherwise noted. PARAMETER SYMBOL TEST CONDITIONS Feedback Voltage VFB 4.5V ≤ VIN ≤ 80V Feedback Bias Current IBIAS(FB) VFB = 0.8V Switch On Resistance RDS(ON) MIN 0.785 Current Limit (4) Oscillator Frequency TYP MAX 0.805 0.825 V 10 nA 32 mΩ Note(4) fSW Fold-Back Frequency VFB = 0.6V 160 VFB = 0V Boot-Strap Voltage VBST - VSW Minimum On Time (5) tON VFB = 1V Under Voltage Lockout Threshold Rising 3.0 Under Voltage Lockout Threshold Hysteresis 200 Supply Current (Quiescent) VEN = 2V, VFB = 1V Thermal Shutdown (5) Note: 4) sense resistor defined 5) Guaranteed by design OPERATION Main Control Loop The TX4138 is a current mode buck regulator. That is, the error amplifier (EA) output voltage is proportional to the peak inductor current. At the beginning of a cycle, the integrated high side power switch M1 is off; the EA output voltage is higher than the current sense amplifier output; and the current comparator’s output is low. The rising edge of the 200KHz clock signal sets the RS Flip-Flop. Its output turns on M1 thus connecting the SW pin and inductor to the input supply. The increasing inductor current is sensed and amplified by the Current Sense Amplifier. Ramp compensation is added to Current Sense Amplifier output and compared to the Error Amplifier output by the PWM Comparator. When the Current Sense UNIT A 200 240 KHz 70 KHz 6 V 100 ns 3.3 3.6 V mV 400 700 μA 160 °C bandgap reference. The polarity is such that a FB pin voltage lower than 0.8V increases the EA output voltage. Since the EA output voltage is proportional to the peak inductor current, an increase in its voltage increases current delivered to the output. An external Schottky Diode (D1) carries the inductor current when internal power MOS is off. APPLICATION INFORMATION Setting the Output Voltage The external resistor divider is used to set the output voltage (see the schematic on front page). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor (see Figure 1). Choose R1 to be around 300kΩ for optimal transient response. R2 is then given by: R2 = R1 VOUT / 0.805 − 1 Table 1 –Resistor Selection for Common Amplifier plus Slope Compensation signal exceeds Vout(V) R1(K Ω) R2(KΩ) the EA output voltage, the RS Flip-Flop is reset and 3.3 300(1%) 96(1%) the TX4138 reverts to its initial M1 off state. If the Current Sense Amplifier plus Slope Compensation 5 300(1%) 57.1(1%) 12 300(1%) 21.4(1%) signal does not exceed the COMP voltage, then the 15 300(1%) 16.9(1%) falling edge of the CLK resets the Flip-Flop. The 24 300(1%) 10.2(1%) output of the Error Amplifier integrates the voltage 32 300(1%) 7.6(1%) difference between the feedback and the 0.8V www.xdssemi.com TX4138_V1.1 第 3 页 TX4138 Selecting the Inductor Loop compensation 33µH to 100µH inductor with a DC current rating of at least 30% percent higher than the maximum load current is recommended for most applications. For highest efficiency, the inductor DC resistance should be less than 50mΩ. For most designs, the inductance value can be derived from the following equation. A 3.3pf-22pf ceramic capacitor connected between FB and OUT can optimize the loop stability for both bandwidth and phase margin, recommended a 4.7pf-12pf ceramic capacitor in most case. L= VOUT × (VIN − VOUT ) VIN × ∆IL × ƒ sw Where ΔIL is the inductor ripple current. Choose inductor current ripple to be approximately 30%-40% of the maximum load current,. The maximum inductor peak current is: POK Power good signal. POK is an open-drain output, can be used as enable signal for next level chip. When FB is less than 90% of 0.8V, PGOOD is low, when output is ready, by connected external pull-up resistor become high to turn on next level chip. VOUT 5V POK ∆IL IL ( MAX ) = Iout ( MAX ) + 2 Selecting the Input Capacitor R1 10KΩ The input capacitor reduces the surge current drawn from the input and also the switching noise from the device. The input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high frequency switching current from pass to the input. For most applications, a 47uF to 100uF electrolytic capacitor is sufficient. Selecting the Output Capacitor The output capacitor keeps output voltage small and ensures regulation loop stability. The output capacitor impedance should be low at the switching frequency. a 220uF-470uF electrolytic capacitor is recommended. ILIM sense resistor Power current flow into the chip via the external accuracy sense resistor which defined the maximum peak current. In guarantee under the normal start up with full load, the sense resistor is recommended use the larger value to ensure less surge current and output output short power dissipation. The sense resistor value should be reduced when used it at low temperature situation to ensure enough startup energy. Table 2 –Sense Resistor Selection Max. output current （A） Rsense（mΩ） 2 30 3 20 4 15 Next level enable PCB Layout 1) Under the large output current and high input voltage case, the schottky diode and the converter is the main heat source, don’t put them too close, the PCB layout should keep enough area for heat dissipation. Recommended ratio is 6:4 for schottky diode and the convertor，for the cost issues, the normal selection of PCB is 1oz thickness, the thick solder tin is benefit on heat dissipation. 2) ILIM is internal connected the power MOS, the heat dissipation should be considered for this pin. 3) The large current path (ILIM 、SW) should be put closer the converter as possible, use short, straight, wide copper foil connect. 4) Input capacitor should be put as close as possible to Vin and GND. 5) The loop of input capacitor, internal power MOS and schottky diode is the highest di/dt radiation region，reduce this region as possible. a 0.1uF ceramic capacitor can be used to form a small loop with internal power MOS and schottky diode, which can reduce the switch ringing caused by PCB parasitic inductor. 6) The outside feedback resistor should be placed nearby the FB pin and keep away from SW node. www.xdssemi.com TX4138_V1.1 第 4 页 TX4138 TYPICAL APPLICATION 3 C1A 100µF 100V C1B VIN 8 BS R3 5.1Ω C3 100nF 2 ILIM R4 0.1µF 20µΩ 100V 6 TX4138 EN SW 5V/3A 1 D1 SS510 L1 33µΗ ILIM(9) POK GND 7 4 C2 C4 12pF R1 300K 1% FB 5 470µF 16V R2 57.1K 1% 5V/2A BOM LIST: Ref Value Description Package Manufacturer Qty Manufacturer P/N C1A 100uF Electrolytic,100V ELC SMD jiang hai 1 VTD-100V100 C1B 0.1uF Ceramic capacitor,100V 0603 muRata 1 GRM188R72A104K C2 470uF Electrolytic,16V ELC SMD jiang hai 1 VTD-16V470 C3 100nF Ceramic capacitor, 100V, X7R 0603 muRata 1 GRM188R72A104K C4 12pF Ceramic, capacitor 50V, X7R 0603 muRata 1 GRM188R71H120K D1 5A Schottky Diode, SS510, 100V, 5A SMC 1 SS510 L1 33uH Inductor CDRH127, 3A,58mΩ CDRH127 1 R1 300KΩ Film Res., 1% 0603 Panasonic 1 ERJ-3EKF3003V R2 57.1KΩ Film Res., 1% 0603 Panasonic 1 ERJ-3EKF5712V R3 5.1Ω Film Res., 1% 0603 Panasonic 1 R4 30mΩ Film Res., 1% 1206 DC-DC convertor ESOP8 U1 1 TX4138 1 Note： recommended to use a low Vf schottky diode for efficiency promotion. 95% 90% EFFICIENCY 85% 80% 75% 70% VOUT=5V VIN=12V VIN=24V VIN=36V VIN=48V VIN=60V 65% 60% 55% 50% 0.0 0.5 1.0 1.5 2.0 2.5 3.0 IOUT(A) www.xdssemi.com TX4138V1.1 第 5 页 TX4138 PCB LAYOUT： www.xdssemi.com TX4138V1.1 第 6 页 TX4138 PACKAGE OUTLINE ESOIC8 PACKAGE OUTLINE AND DIMENSIONS www.xdssemi.com TX4138V1.1 第 7 页