Datasheet LTC3830, LTC3830-1 (Analog Devices) - 8

LTC3830/LTC3830-1
TEST CIRCUITS
5V PVCC VSHDN VCC + 10 0.1 µF µF SHDN VCC PVCC2 PVCC1 IFB IFB VCC PVCC1 PVCC2 NC FB G1 V COMP COMP G1 G1 RISE/FALL NC SS 6800pF 6800pF NC FREQSET LTC3830 LTC3830 NC COMP IMAX G2 V FB FB G2 G2 RISE/FALL 6800pF GND PGND SENSE– SENSE+ IMAX GND PGND 6800pF 3830 F03 3830 F02
Figure 2 Figure 3 U U W U APPLICATIO S I FOR ATIO OVERVIEW THEORY OF OPERATION
The LTC3830 is a voltage mode feedback, synchronous
Primary Feedback Loop
switching regulator controller (see Block Diagram) de- signed for use in high power, low voltage step-down The LTC3830/LTC3830-1 sense the output voltage of the (buck) converters. It includes an onboard PWM generator, circuit at the output capacitor and feeds this voltage back a precision reference trimmed to ±0.8%, two high power to the internal transconductance error amplifier, ERR, MOSFET gate drivers and all necessary feedback and through a resistor divider network. The error amplifier control circuitry to form a complete switching regulator compares the resistor-divided output voltage to the inter- circuit. The PWM loop nominally runs at 200kHz. nal 1.265V reference and outputs an error signal to the PWM comparator. This error signal is compared with a The 16-lead versions of the LTC3830 include a current fixed frequency ramp waveform, from the internal oscil- limit sensing circuit that uses the topside external N-channel lator, to generate a pulse width modulated signal. This power MOSFET as a current sensing element, eliminating PWM signal drives the external MOSFETs through the G1 the need for an external sense resistor. and G2 pins. The resulting chopped waveform is filtered by Also included in the 16-lead version and the LTC3830-1 LO and COUT which closes the loop. Loop compensation is is an internal soft-start feature that requires only a single achieved with an external compensation network at the external capacitor to operate. In addition, 16-lead parts COMP pin, the output node of the error amplifier. feature an adjustable oscillator that can free run or synchronize to external signal with frequencies from
MIN, MAX Feedback Loops
100kHz to 500kHz, allowing added flexibility in external Two additional comparators in the feedback loop provide component selection. The 8-lead version does not in- high speed output voltage correction in situations where clude current limit, internal soft-start and frequency the error amplifier may not respond quickly enough. MIN adjustability. The LTC3830-1 does not include current compares the feedback signal to a voltage 40mV below the limit, frequency adjustability, external synchronization internal reference. If the signal is below the comparator and the shutdown function. threshold, the MIN comparator overrides the error ampli- fier and forces the loop to maximum duty cycle, >91%. 3830fa 8