L6911E 查看數據表（PDF） - STMicroelectronics
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L6911E Datasheet PDF : 34 Pages
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Device description
5
Device description
L6911E
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 ranging 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
1.050V to 1.825V 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/ms
slew rate which permits high converter 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.
5.1
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 tipically 50µA (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 sinked (forced) from (into) the pin.
In particular connecting it to GND the frequency is increased (current is sinked from the pin),
according to the following relationship:
Equation 1
fS
=
200kHz + -4---.--9---4-----⋅---1---0----6-
RT(kΩ)
10/34
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