E-L4978D

L4978 2A STEP DOWN SWITCHING REGULATOR 1 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 2 Features Figure 1. Packages UP TO 2A STEP DOWN CONVERTER OPERATING INPUT VOLTAGE FROM 8V TO 55V PRECISE 3.3V (±1%) INTERNAL REFERENCE VOLTAGE OUTPUT VOLTAGE ADJUSTABLE FROM 3.3V TO 50V SWITCHING FREQUENCY ADJUSTABLE UP TO 300KHz VOLTAGE FEEDFORWARD ZERO LOAD CURRENT OPERATION INTERNAL CURRENT LIMITING (PULSEBYPULSE AND HICCUP MODE) INHIBIT FOR ZERO CURRENT CONSUMPTION PROTECTION AGAINST FEEDBACK DISCONNECTION THERMAL SHUTDOWN SOFT START FUNCTION DIP-8 SO16W Table 1. Order Codes Part Number Package L4978 DIP-8 L4978D SO16 L4978D013TR SO16 in Tape & Reel efficency and high switching speed. A switching frequency up to 300KHz is achievable (the maximum power dissipation of the packages must be observed). A wide input voltage range between 8V to 55V and output voltages regulated from 3.3V to 50V cover the majority of today’s applications. Features of this new generations of DCDC converter include pulse-by-pulse current limit, hiccup mode for short circuit protection, voltage feedforward regulation, soft-start, protection against feedback loop disconnection, inhibit for zero current consumption and thermal shutdown. DESCRIPTION The L4978 is a step down monolithic power switching regulator delivering 2A at a voltage between 3.3V and 50V (selected by a simple external divider). Realized in BCD mixed technology, the device uses an internal power D-MOS transistor (with a typical Rdson of 0.25Ω) to obtain very high The device is available in plastic dual in line, DIP8 for standard assembly, and SO16W for SMD assembly. Figure 2. Typical Application Circuit Vi=8V to 55V 5 8 R1 20K L4978 3 C1 220µF 63V C7 220nF C2 2.7nF C5 100nF 2 4 1 7 R2 9.1K C4 22nF L1 126µH (77120) 6 C6 100nF D1 ST PS3L60U VO=3.3V/2A C8 330µF D98IN837A May 2005 Rev. 9 1/13 L4978 Table 2. Block Diagram VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE 2 SS_INH INHIBIT SOFTSTART 3.3V INTERNAL REFERENCE INTERNAL SUPPLY 5.1V 7 COMP 6 E/A 8 FB PWM R 3.3V Q S CBOOT CHARGE AT LIGHT LOADS DRIVE OSCILLATOR 1 3 OSC BOOT 4 GND D97IN594 OUT Figure 3. Pins Connection (Top view) N.C. 1 16 N.C. GND 2 15 N.C. SS_INH 3 14 FB GND 1 8 FB SS_INH 2 7 COMP OSC 4 13 COMP OSC 3 6 BOOT OUT 5 12 BOOT OUT 4 5 VCC OUT 6 11 VCC N.C. 7 10 N.C. N.C. 8 9 N.C. D97IN595 D97IN596 DIP-8 SO16W Table 3. Pin Description N° Pin Name 1 2 GND 2 3 SS_INH A logic signal (active low) disables the device (sleep mode operation). A capacitor connected between this pin and ground determines the soft start time. When this pin is grounded disables the device (driven by open collector/drain). 3 4 OSC An external resistor connected between the unregulated input voltage and this pin and a capacitor connected from this pin to ground fix the switching frequency. (Line feed forward is automatically obtained) 2/13 Function Ground L4978 Table 3. Pin Description (continued) N° Pin Name Function 4 5, 6 OUT Stepdown regulator output 5 11 VCC Unregulated DC input voltage 6 12 BOOT A capacitor connected between this pin and OUT allows to drive the internal DMOS Transistors 7 13 COMP E/A output to be used for frequency compensation 8 14 FB Stepdown feedback input. Connecting directly to this pin results in an output voltage of 3.3V. An external resistive divider is required for higher output voltages. (*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die. Table 4. Thermal Data Symbol Rth(j-amb) Parameter Thermal Resistance Junction to ambient Minidip SO16 Unit 90 (*) 110 (*) °C/W Max. (*) Package mounted on board. Table 5. Absolute Maximum Ratings Symbol Parameter Minidip S016 V5 V11 V4 V5,V6 I4 I5,I6 V6-V5 V12-V11 V6 V12 V7 Value Unit Input voltage 58 V Output DC voltage Output peak voltage at t = 0.1ms f=200KHz -1 -5 V V Maximum output current int. limit. 14 V Bootstrap voltage 70 V V13 Analogs input voltage (VCC= 24V) 12 V V2 V3 Analogs input voltage (VCC= 24V) 13 V V8 V14 (VCC= 20V) 6 -0.3 V V 1 0.8 W W -40 to 150 °C Ptot Power dissipation a Tamb ≤ 60°C Tj,Tstg Junction and storage temperature DIP-8 SO16 3/13 L4978 Table 6. Electrical Characteristcs (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified). “● " Specification Referred to Tj from 0 to 125°C Symbol Parameter Test Condition Min. Typ. Max. Unit 55 V DYNAMIC CHARACTERISTIC VI Operating input voltage range Vo = 3.3 to 50V; Io = 2A Vo Output voltage Io = 0.5A ● Io = 0.2 to 2A Vcc = 8 to 55V Vd Dropout voltage Vcc = 10V; Io = 2A Maximum limiting current Vcc = 8 to 55V Efficiency Vo = 3.3V; Io= 2A ● 8 3.33 3.36 3.39 V 3.292 3.36 3.427 V 3.22 3.36 3.5 V 0.58 0.733 V ● Il fs SVRR ● 3 1.173 V 3.5 A 87 ● Switching frequency 2.5 90 100 % 110 60 KHz dB Supply voltage ripple rejection Vi = Vcc+2VRMS; Vo= Vref; Io = 2.5A; f ripple= 100Hz Switching Frequency Stability vs. Vcc Vcc = 8 to 55V 3 Temp. stability of switching frequency Tj = 0 to 125°C 4 6 % % SOFT START Soft start charge current 30 40 50 µA Soft start discharge current 6 10 14 µA INHIBIT VLL Low level voltage ● IsLL Isource Low level ● 0.9 V 5 15 µA 4 6 mA DC CHARACTERISTICS Iqop Iq Iqst-by Total operating quiescent current Quiescent current Duty Cycle = 0; VFB= 3.8V 2.5 3.5 mA Total stand-by quiescent current Vinh < 0.9V 100 200 µA Vcc = 55V; Vinh