L6910(2003) 查看數據表（PDF） - STMicroelectronics

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L6910
(Rev.:2003)

ADJUSTABLE STEP DOWN CONTROLLER WITH SYNCHRONOUS RECTIFICATION

STMicroelectronics 

L6910A L6910

Device Description

The device is an integrated circuit realized in BCD technology. The controller provides complete control 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 error 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 de-

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

sensing resistor. The device is available in SO16 narrow 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 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:

fOSC,RT = 200KH z + -4--R-.-9--T--4-(---K-⋅---1Ω---0--)--6-

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

to the following relationships:

fOSC,RT = 200KH z – -4---.R-3----T0---(6---K--⋅--Ω-1---0-)---7-

VCC = 12V

fOSC,RT = 200KH z – -R1---5-T---(-⋅--K-1---Ω-0---6-)-

VCC = 5V

Switching frequency variation vs. RT are repeated in Fig. 1.

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

oscillator.

Figure 1.

Reference

10000

1000

100

10

10

RT to GND

RT to VCC=12V

RT to VCC=5V

100

Frequency [kHz]

A precise ±1.5% 0.9V reference is available. This ref-

erence must be filtered with 1nF ceramic capacitor to

avoid instability in the internal linear regulator. It is

able to deliver up to 100µA and may be used as ref-

erence for the device regulation and also for other de-

vices. If forced under 70% of its nominal value, the

device enters in Hiccup mode until this condition is

removed.

Through the EAREF pin the reference for the regula-

tion is taken. This pin directly connects the non-in-

verting input of the error amplifier. An external

reference (or the internal 0.9V ±1.5%) may be used.

The input for this pin can range from 0.9V to 3V. It

has an internal pull-down (300kΩ resistor) that forces

the device shutdown if no reference is connected (pin

1000

floating). However the device is shut down if the volt-

age on the EAREF pin is lower than 650mV (typ).

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