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6269CRZ Просмотр технического описания (PDF) - Intersil

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6269CRZ High-Performance Notebook PWM Controller with Bias Regulator and Audio-Frequency Clamp Intersil
Intersil Intersil
6269CRZ Datasheet PDF : 17 Pages
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ISL6269
Theory of Operation
Modulator
The ISL6269 is a hybrid of fixed frequency PWM control, and
variable frequency hysteretic control. The term “Ripple” in
the name “Robust-Ripple-Regulator” refers to the converter
output inductor ripple current, not the converter output ripple
voltage. The output voltage is regulated to 600mV at the FB
pin with respect to the GND pin. The FB pin is the inverting
input of the error amplifier. The frequency response of the
feedback control loop is tuned with a type-two compensation
network connected across the FB pin and COMP pin.
The R3 modulator synthesizes an AC signal VR, which is an
ideal representation of the output inductor ripple current. The
duty-cycle of VR is derived from the voltage measured at the
VIN pin and VO pin with respect to the GND pin.
Transconductance amplifiers convert the VIN and VO
voltages into currents that charge and discharge the ripple
capacitor CR. The positive slope of VR can be written as:
VRPOS = (gm) (VIN VO)
(EQ. 1)
The negative slope of VR can be written as:
VRNEG = gm VO
(EQ. 2)
A voltage VW is referenced with respect to the error amplifier
output voltage VCOMP, creating a window-voltage envelope
into which voltage VR is compared. The VR, VCOMP, and VW
signals feed into a hysteretic window comparator in which
VCOMP is the lower threshold voltage and VW is the higher
threshold voltage. PWM pulses are generated as VR
traverses the VW and VCOMP thresholds. The charging and
discharging rates of capacitor CR determine the PWM
switching frequency for a given amplitude of VW with respect
to VCOMP. The R3 regulator simultaneously affects switching
frequency and duty cycle because it modulates both edges
of the PWM pulses.
RIPPLE CAPACITOR VOLTAGE CR
WINDOW VOLTAGE VW
ERROR AMPLIFIER VOLTAGE VCOMP
PWM
µs
FIGURE 3. MODULATOR WAVEFORMS DURING LOAD TRANSIENT
9
FN9177.1
August 7, 2006
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