L6919C Просмотр технического описания (PDF) - STMicroelectronics

Номер в каталоге

Компоненты Описание

производитель

L6919C

5 BIT PROGRAMMABLE DUAL-PHASE CONTROLLER WITH DYNAMIC VID MANAGEMENT

STMicroelectronics 

L6919C

DEVICE DESCRIPTION

The device is an integrated circuit realized in BCD technology. It provides complete control logic and protections

for a high performance dual-phase step-down DC-DC converter optimized for microprocessor power supply. It

is designed to drive N Channel MOSFETs in a dual-phase synchronous-rectified buck topology. A 180 deg

phase shift is provided between the two phases allowing reduction in the input capacitor current ripple, reducing

also the size and the losses. The output voltage of the converter can be precisely regulated, programming the

VID pins, from 0.800V to 1.550V with 25mV binary steps, with a maximum tolerance of ±0.6% over temperature

and line voltage variations. The device manages On-The-Fly VID Code changes stepping to the new configu-

ration following the VID table with no need for external components. The device provides an average current-

mode control with fast transient response. It includes a 200kHz free-running oscillator. The error amplifier fea-

tures a 15V/µs slew rate that permits high converter bandwidth for fast transient performances. Current infor-

mation is read across the lower mosfets RdsON or across a sense resistor in fully differential mode. The current

information corrects the PWM output in order to equalize the average current carried by each phase. Current

sharing between the two phases is then limited at ±10% over static and dynamic conditions. The device protects

against Over-Current, with an OC threshold for each phase, entering in constant current mode. Since the current

is read across the low side mosfets, the constant current keeps constant the bottom of the inductors current

triangular waveform. When an under voltage is detected the device latches and the FAULT pin is driven high.

The device performs also Over-Voltage protection that disables immediately the device turning ON the lower

driver and driving high the FAULT pin.

OSCILLATOR

The switching frequency is internally fixed to 200kHz. The internal oscillator generates the triangular waveform for the

PWM charging and discharging with a constant current an internal capacitor. The current delivered to the oscillator is

typically 17µA (Fsw=200KHz) and may be varied using an external resistor (ROSC) connected between OSC pin and

GND or Vcc. Since the OSC pin is maintained at fixed voltage (Typ. 1.235V), the frequency is varied proportionally to

the current sunk (forced) from (into) the pin considering the internal gain of 12KHz/µA.

In particular connecting it to GND the frequency is increased (current is sunk from the pin), while connecting ROSC

to Vcc=12V the frequency is reduced (current is forced into the pin), according to the following relationships:

ROSCvs. GND: fS = 200kH z + -R----O---1-S--.--C2---3-(--K-7----Ω----)- ⋅ 12k--µ--H--A---z- = 200 kHz + -R1---4-O---.-S8----2C----(⋅--K-1----Ω0---6--)

ROSC vs. 12V: fS = 200 kHz – -R-1---O2----S-–---C-1---(-.-K2----3-Ω--7--)- ⋅ 12 k--µ--H--A---z- = 200kH z – -1-R--2--O-.--9-S--1--C-8---(--⋅K---1--Ω--0---)7-

Note that forcing a 17µA current into this pin, the device stops switching because no current is delivered to the

oscillator.

Figure 1. ROSC vs. Switching Frequency

7000

6000

5000

4000

3000

2000

1000

0

0

50

100

150

200

Frequency (KHz)

1000

800

600

400

200

0

200

300

400

500

600

Frequency (KHz)

8/32

Share Link: