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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/
µ
sec 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-
current conditions entering in HICCUP mode. The device monitors the current by using the r
DS(ON)
of the upper
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
µ
A (Fsw=200KHz) and may be varied using an external resistor (R
T
) connected between
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)
01111
1.30
11111Output Off
01110
1.35
11110 2.1
01101
1.40
11101 2.2
01100
1.45
11100 2.3
01011
1.50
11011 2.4
01010
1.55
11010 2.5
01001
1.60
11001 2.6
01000
1.65
11000 2.7
00111
1.70
10111 2.8
00110
1.75
10110 2.9
00101
1.80
10101 3.0
00100
1.85
10100 3.1
00011
1.90
10011 3.2
00010
1.95
10010 3.3
00001
2.00
10001 3.4
00000
2.05
10000 3.5
f
S
200kHz
4.94 10
6
⋅
R
T
k
Ω()
-------------------------+=
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