L4971_05

L4971 1.5A STEP DOWN SWITCHING REGULATOR 1 ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ FEATURES UP TO 1.5A 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. Package DIP8 SO16W Table 1. Order Codes Part Number L4971 L4971D L4971D013TR Package DIP8 SO16W SO16 in Tape & Reel 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 DC-DC 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 L4971 is a step down monolithic power switching regulator delivering 1.5A 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 efficency and high switching speed. Figure 1. Block Diagram Vi=8V to 55V 5 R1 20K 3 C1 220µF 63V C7 220nF C2 2.7nF 2 7 8 L4971 4 1 6 L1 126µH (77120) D1 STPS 3L60U C8 330µF VO=3.3V/1.5A C5 100nF R2 9.1K C4 22nF C6 100nF D97IN748A May 2005 Rev. 11 1/13 L4971 Figure 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. Pin Connections N.C. GND 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. GND SS_INH OSC OUT 1 2 3 4 D97IN595 8 7 6 5 FB COMP BOOT VCC SS_INH OSC OUT OUT N.C. N.C. DIP8 SO16 Table 2. Pin Description DIP 1 2 SO (*) 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 disabled 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) Stepdown regulator output Unregulated DC input voltage A capacitor connected between this pin and OUT allows to drive the internal DMOS Transistor 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 3 4 OSC 4 5 6 7 8 5, 6 11 12 13 14 OUT VCC BOOT COMP FB (*) Pins 1, 7, 8, 9, 10, 15 and 16 are not internally, electrically connected to the die. 2/13 L4971 Table 3. Absolute Maximum Ratings Symbol Minidip V5 V4 I4 V6-V5 V6 V7 V2 V8 Ptot Tj,Tstg 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 Junction and storage temperature DIP8 SO16 Input voltage Output DC voltage Output peak voltage at t = 0.1µs f=200KHz Maximum output current Parameter Value 58 -1 -5 int. limit. 14 70 12 13 6 -0.3 1 0.8 -40 to 150 V V V V V V W W °C Unit V V V Table 4. Thermal Data Symbol Rth(j-amb) Parameter Thermal Resistance Junction to ambient Max. DIP8 90 (*) SO16 110 (*) Unit °C/W (*) Package mounted on board. 3 ELECTRICAL CHARACTERISTCS Table 5. (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified.) * Specification Refered to Tj from 0 to 125°C Symbol Parameter Test Condition Min. Typ. Max. Unit DYNAMIC CHARACTERISTIC VI Vo Operating input voltage range Output voltage Vo = 3.3 to 50V; Io = 1.5A Io = 0.5A Io = 0.2 to 1.5A Vcc = 8 to 55V Vd Dropout voltage Vcc = 10V; Io = 1.5A * Il Maximum limiting current Efficiency Switching frequency Supply voltage ripple rejection Voltage stability of switching frequency Temp. stability of switching frequency Vi = Vcc+2VRMS; Vo = Vref; Io = 1.5A; f ripple = 100Hz Vcc = 8 to 55V Tj = 0 to 125°C Vcc = 8 to 55V Vo = 3.3V; Io = 1.5A * 90 60 3 4 6 * 2 2.5 85 100 110 * * 8 3.33 3.292 3.22 3.36 3.36 3.36 0.44 55 3.39 3.427 3.5 0.55 0.88 3 V V V V V V A % KHz dB % % fs SVRR 3/13 L4971 Table 5. (Tj = 25°C, Cosc = 2.7nF, Rosc = 20kΩ, VCC = 24V, unless otherwise specified.) * Specification Refered to Tj from 0 to 125°C Soft Start Soft start charge current Soft start discharge current Inhibit VLL IsLL Low level voltage Isource Low level * * 5 0.9 15 V µA 30 6 40 10 50 14 µA µA DC Characteristics Iqop Iq Iqst-by Total operating quiescent current Quiescent current Total stand-by quiescent current Duty Cycle = 0; VFB = 3.8V Vinh