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L6911D
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 1.100V to 1.850V
with 25mV binary steps, with a maximum tolerance of ±1% over temperature 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/
s slew rate which permits high convert-
er bandwidth for fast transient 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 rDS(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
A (Fsw=200KHz) and may be varied using an external resistor (RT) 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)
11111
Output OFF
0111
1
1.475
11110
1.100
0111
0
1.500
11101
1.125
0110
1
1.525
11100
1.150
0110
0
1.550
11011
1.175
0101
1
1.575
11010
1.200
0101
0
1.600
11001
1.225
0100
1
1.625
11000
1.250
0100
0
1.650
10111
1.275
0011
1
1.675
10110
1.300
0011
0
1.700
10101
1.325
0010
1
1.725
10100
1.350
0010
0
1.750
10011
1.375
0001
1
1.775
10010
1.400
0001
0
1.800
10001
1.425
0000
1
1.825
10000
1.450
0000
0
1.850
f
S
200kH z
4.94 10
6
R
T k
()
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+
=