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L6911C

Table 1. VID Settings

Device Description

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

for a high performance step-down DC-DC converter optimized for microprocessor power supply. It is designed

to drive N-Channel Mosfets in a synchronous-rectified buck topology. The device works properly with Vcc rang-

ing from 5V to 12V and regulates the output voltage starting from a 1.26V power stage supply voltage (Vin). The

output voltage of the converter can be precisely regulated, programming the VID pins, from 1.3V to 2.05V with

50mV binary steps and from 2.1V to 3.5V with 100mV binary steps, with a maximum tolerance of ±1% over tem-

perature and line voltage variations. The device provides voltage-mode control with fast transient response. It

includes a 200kHz free-running oscillator that is adjustable from 50kHz to 1MHz. The error amplifier features a

15MHz gain-bandwidth product and 10V/

µsec slew rate which permits high converter bandwidth for fast tran-

sient performance. The resulting PWM duty cycle ranges from 0% to 100%. The device protects against over-

MOSFET which eliminates the need for a current sensing resistor.

The device is available in SO20 package.

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 50

RT pin and GND or VCC. Since the RT pin is maintained at fixed voltage (typ. 1.235V), the frequency is varied

proportionally to the current sunk (forced) from (into) the pin.

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

following relationship:

Connecting RT to VCC=12V or to VCC=5V the frequency is reduced (current is forced into the pin), according

to the following relationships:

VID4

VID3

VID2

VID1

VID0

Output

Voltage (V)

VID4

VID3

VID2

VID1

VID0

Output

Voltage (V)

01

11

1

1.30

11111

Output Off

01

11

0

1.35

11110

2.1

01

10

1

1.40

11101

2.2

01

10

0

1.45

11100

2.3

01

01

1

1.50

11011

2.4

01

01

0

1.55

11010

2.5

01

00

1

1.60

11001

2.6

01

00

0

1.65

11000

2.7

00

11

1

1.70

10111

2.8

00

11

0

1.75

10110

2.9

00

10

1

1.80

10101

3.0

00

10

0

1.85

10100

3.1

00

01

1

1.90

10011

3.2

00

01

0

1.95

10010

3.3

00

00

1

2.00

10001

3.4

00

00

0

2.05

10000

3.5

f

S

200kH z

4.94 10

6

⋅

R

()

-------------------------

+

=