L4978D

L4978 2A STEP DOWN SWITCHING REGULATOR 1 ■ ■ Features 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 Figure 1. Packages ■ DIP-8 SO16W ■ Table 1. Order Codes Part Number L4978 L4978D L4978D013TR Package DIP-8 SO16 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. The device is available in plastic dual in line, DIP8 for standard assembly, and SO16W for SMD assembly. ■ ■ ■ 2 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 Figure 2. Typical Application Circuit Vi=8V to 55V 5 R1 20K 3 C1 220µF 63V C7 220nF C2 2.7nF 2 7 8 L4978 4 1 6 L1 126µH (77120) D1 ST PS3L60U C8 330µF VO=3.3V/2A C5 100nF R2 9.1K C4 22nF C6 100nF D98IN837A May 2005 Rev. 9 1/13 L4978 Table 2. Block Diagram VCC 5 THERMAL SHUTDOWN VOLTAGES MONITOR CBOOT CHARGE SS_INH 2 INHIBIT SOFTSTART 3.3V COMP FB 7 8 E/A INTERNAL REFERENCE INTERNAL SUPPLY 5.1V 6 PWM BOOT R S 3.3V Q DRIVE OSCILLATOR 1 GND CBOOT CHARGE AT LIGHT LOADS 3 OSC 4 OUT D97IN594 Figure 3. Pins Connection (Top view) N.C. GND GND SS_INH OSC OUT 1 2 3 4 D97IN595 1 2 3 4 5 6 7 8 D97IN596 16 15 14 13 12 11 10 9 N.C. N.C. FB COMP BOOT VCC N.C. N.C. 8 7 6 5 FB COMP BOOT VCC SS_INH OSC OUT OUT N.C. N.C. DIP-8 SO16W Table 3. Pin Description N° 1 2 Pin 2 3 Name GND SS_INH Ground 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). 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) Function 3 4 OSC 2/13 L4978 Table 3. Pin Description (continued) N° 4 5 6 7 8 Pin 5, 6 11 12 13 14 Name OUT VCC BOOT COMP FB Stepdown regulator output Unregulated DC input voltage A capacitor connected between this pin and OUT allows to drive the internal DMOS Transistors E/A output to be used for frequency compensation 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. Function (*) 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) (*) Package mounted on board. Parameter Thermal Resistance Junction to ambient Max. Minidip 90 (*) SO16 110 (*) Unit °C/W Table 5. Absolute Maximum Ratings Symbol Parameter Minidip V5 V4 I4 V6-V5 V6 V7 V2 V8 Ptot S016 V11 V5,V6 I5,I6 V12-V11 V12 V13 V3 V14 Bootstrap voltage Analogs input voltage (VCC= 24V) Analogs input voltage (VCC= 24V) (VCC= 20V) Power dissipation a Tamb ≤ 60°C DIP-8 SO16 Junction and storage temperature 1 0.8 -40 to 150 W W °C Input voltage Output DC voltage Output peak voltage at t = 0.1ms f=200KHz Maximum output current 14 70 12 13 6 -0.3 58 -1 -5 int. limit. V V V V V V V V V Value Unit Tj,Tstg 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 VI Vo Parameter Operating input voltage range Output voltage Test Condition Vo = 3.3 to 50V; Io = 2A Io = 0.5A ● Min. 8 3.33 3.292 ● Typ. Max. 55 Unit V V V V V V A % KHz dB DYNAMIC CHARACTERISTIC 3.36 3.36 3.36 0.58 ● ● 3.39 3.427 3.5 0.733 1.173 3.5 110 Io = 0.2 to 2A Vcc = 8 to 55V Vd Dropout voltage Maximum limiting current Efficiency fs SVRR Switching frequency Supply voltage ripple rejection Switching Frequency Stability vs. Vcc Temp. stability of switching frequency SOFT START Soft start charge current Soft start discharge current INHIBIT VLL IsLL Iqop Iq Iqst-by Low level voltage Isource Low level Total operating quiescent current Quiescent current Total stand-by quiescent current Duty Cycle = 0; VFB= 3.8V Vinh < 0.9V Vcc = 55V; Vinh