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L6910 - L6910A

4

DEVICE DESCRIPTION

The device is an integrated circuit realized in BCD technology. The controller provides complete con-

trol logic and protection for a high performance step-down DC-DC converter. It is designed to drive N

Channel Mosfets in a synchronous-rectified buck topology. The output voltage of the converter can be

precisely regulated down to 900mV with a maximum tolerance of ±1.5% when the internal reference is

used (simply connecting together EAREF and VREF pins). The device allows also using an external

reference (0.9V to 3V) for the regulation. 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 er-

ror amplifier features a 10MHz gain-bandwidth product and 10V/

µs slew rate that permits to realize

high converter bandwidth for fast transient performance. The PWM duty cycle can range from 0% to

100%. The device protects against over-current conditions entering in HICCUP mode. The device

rent sensing resistor. The device is available in SO16 narrow package.

4.1 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 typically 50

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

following relationship:

to the following relationships:

Switching frequency variation vs. RT are repeated in Fig. 4.

Note that forcing a 50

µA current into this pin, the device stops switching because no current is delivered to the

oscillator.

Figure 4.

f

OS C,RT

200KHz

4.94 10

6

⋅

R

()

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

+

=

f

OS C,RT

200KHz

4.306 10

7

⋅

R

()

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

–

=

f

OS C,RT

200KHz

15 10

6

⋅

R

()

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

–

=

10

100

1000

Frequency [kHz]

10

100

1000

10000

RT to GND

RT to VCC=12V

RT to VCC=5V