AN2208 datasheet(46/51 Pages) STMICROELECTRONICS

46 / 51 page

7 Test results

AN2208

46/51

Appendix C L5970D DC/DC converter

C.1

Functional description

The L5970D (Figure 56) is a step-down power regulator capable of delivering output voltages

from 1.235 to 35V (up to 1A). The operating input voltage ranges from 4.4 to 36V. It is designed

in BCD5 technology and the power switching element is a P-Channel D-MOS power transistor.

An internal oscillator sets the switching frequency at 250 kHz, minimizing the LC output filter.

The L5970D is used for supplying optocouplers and other applications.

The VN808 and VN340SP reference design boards use the L5970D DC/DC Converter for the

power supplies for the data parts. With an output voltage of 6V and output current up to 1A, the

L5970D is an attractive and simple solution.

The main internal blocks are shown in Figure 56 where is reported the device block diagram.

They are:

●

A voltage regulator that supplies the internal circuitry. From this regulator a 3.3V reference

voltage is externally available.

●

A voltage monitor circuit that checks the input and internal voltages.

●

A fully integrated sawtooth oscillator whose frequency is 250 kHz ±5%, including also the

voltage feed forward function and an input/output synchronization pin.

●

Two embedded current limitations circuitries which control the current that flows through

the power switch. The Pulse by Pulse Current Limit forces the power switch OFF cycle by

cycle if the current reaches an internal threshold, while the Frequency Shifter reduces the

switching frequency in order to strongly reduce the duty cycle.

●

A transconductance error amplifier.

●

A pulse width modulator (PWM) comparator and the relative logic circuitry necessary to

drive the internal power.

●

A high-side driver for the internal P-MOS switch.

●

An inhibitor block for stand-by operation.

●

A circuit to provide the thermal protection function.

Figure 56. L5970D block diagram

INHIBIT

VOLTAGE

MONITOR

PEAK TO PEAK

CURRENT LIMIT

THERMAL

SHUTDOWN

E/A

PWM

1.235V

OSCILLATOR

FREQUENCY

SHIFTER

TRIMMING

SUPPLY

1.235V 3.5V

DRIVER

VREF

BUFFER

LPDMOS

POWER

SYNC

COMP

INH

VREF

VCC

Ai11607

OUT

GND

AN2208 Datasheet(PDF) 46 Page - STMicroelectronics

AN2208 Datasheet(HTML) 46 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

Datasheet Download

Link URL