3/22

L4972A

Table 3. Absolute Maximum Ratings

(*) SO-20

Table 4. Thermal Data

3

Circuit Operation

The L4972A is a 2A monolithic stepdown switching regulator working in continuous mode realized in the

new BCD Technology. This technology allows the integration of isolated vertical DMOS power transistors

plus mixed CMOS/Bipolar transistors.

The device can deliver 2A at an output voltage adjustable from 5.1V to 40V and contains diagnostic and

control functions that make it particularly suitable for microprocessor based systems.

3.1 BLOCK DIAGRAM

The block diagram shows the DMOS power transistors and the PWM control loop. Integrated functions

include a reference voltage trimmed to 5.1V ± 2%, soft start, undervoltage lockout, oscillator with feedfor-

ward control, pulse by pulse current limit, thermal shutdown and finally the reset and power fail circuit. The

reset and power fail circuit provides an output signal for a microprocessor indicating the status of the sys-

tem.

Device turn on is around 11V with a typical 1V hysterysis, this threshold porvides a correct voltage for the

driving stage of the DMOS gate and the hysterysis prevents instabilities.

An external bootstrap capacitor charge to 12V by an internal voltage reference is needed to provide cor-

rect gate drive to the power DMOS. The driving circuit is able to source and sink peak currents of around

0.5A to the gate of the DMOS transistor. A typical switching time of the current in the DMOS transistor is

50ns. Due to the fast commutation switching frequencies up to 200kHz are possible.

The PWM control loop consists of a sawtooth oscillator, error amplifier, comparator, latch and the output

Symbol

Parameter

Value

Unit

Input Voltage

55

V

Input Operating Voltage

50

V

Output DC Voltage

Output Peak Voltage at t = 0.1

µs f = 200kHz

-1

-5

V

V

Maximum Output Current

Internally Limited

Boostrap Voltage

Boostrap Operating Voltage

65

V

V

Input Voltage at Pins 4, 12

12

V

Reset Output Voltage

50

V

Reset Output Sink Current

50

mA

Input Voltage at Pin 2, 7, 9, 10

7

V

Reset Delay Sink Current

30

mA

Error Amplifier Output Sink Current

1

A

Soft Start Sink Current

30

mA

at Tamb = 70°C (No copper area on PCB)

5 / 3.75(*)

1.3/1 (*)

W

W

Junction and Storage Temperature

-40 to 150

°C

Symbol

Parameter

PowerDIP

SO20

Unit

Thermal Resistance Junction-Pins

max,

12

16

°C/W

Thermal Resistance Junction-ambient

max,

60

80

°C/W