L6910 データシートの表示（PDF） - STMicroelectronics

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L6910

ADJUSTABLE STEP DOWN CONTROLLER WITH SYNCHRONOUS RECTIFICATION

STMicroelectronics 

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

monitors the current by using the rDS(ON) of the upper MOSFET(s) that eliminates the need for a cur-

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 50µA (Fsw = 200KHz) and may be varied using an external resistor (RT) connected between

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

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

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

following relationship:

f O S C ,RT

=

200KHz + 4----.-9----4-----⋅---1---0----6-

RT(KΩ)

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

to the following relationships:

fO S C ,RT

=

200KHz – -4---.--3---0---6-----⋅---1---0----7-

RT(KΩ)

VCC = 12V

fOSC,RT = 200KHz – R-1---5-T---(-⋅--K-1---Ω0----6-)-

VCC = 5V

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

Note that forcing a 50µA current into this pin, the device stops switching because no current is delivered to the

oscillator.

Figure 4.

10000

1000

100

10

10

RT to GND

RT to VCC=12V

RT to VCC=5V

100

Frequency [kHz]

1000

5/29

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