PDF LTC3827-1 Data sheet ( Hoja de datos )

Número de pieza	LTC3827-1
Descripción	2-Phase Synchronous Step-Down Controller
Fabricantes	Linear Technology
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LTC3827-1 Low IQ, Dual, 2-Phase Synchronous Step-Down Controller FEATURES DESCRIPTION wwwn.daWtasihdeeet4Ouu.ctopmut Voltage Range: 0.8V ≤ VOUT ≤ 10V n Low Operating IQ: 80μA (One Channel On) n Out-of-Phase Controllers Reduce Required Input Capacitance and Power Supply Induced Noise n OPTI-LOOP® Compensation Minimizes COUT n ±1% Output Voltage Accuracy n Wide VIN Range: 4V to 36V Operation n Phase-Lockable Fixed Frequency 140kHz to 650kHz n Selectable Continuous, Pulse-Skipping or Low Ripple Burst Mode® Operation at Light Loads n Dual N-Channel MOSFET Synchronous Drive n Very Low Dropout Operation: 99% Duty Cycle n Adjustable Output Voltage Soft-Start or Tracking n Output Current Foldback Limiting n Power Good Output Voltage Monitor n Output Overvoltage Protection n Low Shutdown IQ: 8μA n Internal LDO Powers Gate Drive from VIN or VOUT n Small 28-Lead SSOP Package APPLICATIONS n Automotive Systems n Battery-Operated Digital Devices n Distributed DC Power Systems The LTC®3827-1 is a high performance dual step-down switching regulator controller that drives all N-channel synchronous power MOSFET stages. A constant frequency current mode architecture allows a phase-lockable fre- quency of up to 650kHz. Power loss and noise due to the ESR of the input capacitor ESR are minimized by operating the two controller output stages out of phase. The 80μA no-load quiescent current extends operating life in battery-powered systems. OPTI-LOOP compensa- tion allows the transient response to be optimized over a wide range of output capacitance and ESR values. The LTC3827-1 features a precision 0.8V reference and a power good output indicator. A wide 4V to 36V input supply range encompasses all battery chemistries. Independent TRACK/SS pins for each controller ramp the output voltage during start-up. Current foldback limits MOSFET heat dissipation during short-circuit conditions. The PLLIN/MODE pin selects among Burst Mode opera- tion, pulse-skipping mode, or continuous inductor cur- rent mode at light loads. For a leadless package version (5mm × 5mm QFN) with additional features, see the LTC3827 data sheet. L, LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 5929620, 6177787, 6144194, 5408150, 6580258, 6304066, 5705919. TYPICAL APPLICATION VOUT1 3.3V 5A 3.3μH 0.015Ω 62.5k 150μF High Efﬁciency Dual 8.5V/3.3V Step-Down Converter + 4.7μF 0.1μF VIN TG1 BOOST1 SW1 INTVCC TG2 BOOST2 SW2 1μF 0.1μF 22μF 50V VIN 4V TO 36V 7.2μH BG1 BG2 LTC3827-1 PGND SENSE1+ SENSE2+ 0.015Ω SENSE1– SENSE2– VFB1 VFB2 ITH1 ITH2 20k 220pF TRACK/SS1 SGND TRACK/SS2 15k 0.1μF 0.1μF 220pF 15k 192.5k 20k VOUT2 8.5V 3.5A 150μF 38271 TA01 Efﬁciency and Power Loss vs Load Current 100 100000 90 EFFICIENCY VIN = 12V; VOUT = 3.3V 10000 80 70 1000 60 50 100 40 30 POWER LOSS 10 20 1 10 0 0.001 0.01 0.1 1 10 100 LOAD CURRENT (mA) 0.1 1000 10000 38271 TA01b FIGURE 13 CIRCUIT 38271fe 1 1 page TYPICAL PERFORMANCE CHARACTERISTICS LTC3827-1 Load Step (Burst Mode Operation) www.datasheet4u.com VOUT 100mV/DIV AC COUPLED Load Step (Forced Continuous Mode) VOUT 100mV/DIV AC COUPLED Load Step (Pulse Skip Mode) VOUT 100mV/DIV AC COUPLED IL 2A/DIV 20μs/DIV FIGURE 13 CIRCUIT VOUT = 3.3V IL 2A/DIV 38271 G04 20μs/DIV FIGURE 13 CIRCUIT VOUT = 3.3V IL 2A/DIV 38271 G05 20μs/DIV FIGURE 13 CIRCUIT VOUT = 3.3V 38271 G06 Inductor Current at Light Load FORCED CONTINUOUS MODE 2A/DIV BURST MODE PULSE SKIPPING MODE 4μs/DIV FIGURE 13 CIRCUIT VOUT = 3.3V ILOAD = 300μA 38271 G07 Soft Start-Up VOUT2 2V/DIV VOUT1 2V/DIV 20ms/DIV FIGURE 13 CIRCUIT 38271 G08 Tracking Start-Up VOUT2 2V/DIV VOUT1 2V/DIV 20ms/DIV FIGURE 13 CIRCUIT 38271 G09 Total Input Supply Current vs Input Voltage 350 300 250 300μA LOAD 200 150 100 NO LOAD 50 0 5 10 15 20 25 INPUT VOLTAGE (V) FIGURE 13 CIRCUIT 30 35 38271 G10 EXTVCC Switchover and INTVCC Voltages vs Temperature 6.0 5.8 5.6 5.4 INTVCC 5.2 5.0 4.8 EXTVCC RISING 4.6 4.4 EXTVCC FALLING 4.2 4.0 –45 –25 –5 15 35 55 75 95 TEMPERATURE (°C) 38271 G11 INTVCC Line Regulation 5.50 5.45 5.40 5.35 5.30 5.25 5.20 5.15 5.10 5.05 5.00 0 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V) 38271 G12 38271fe 5 5 Page LTC3827-1 OPERATION (Refer to Functional Diagram) When the ITH voltage drops below 0.4V, the internal sleep signal goes high (enabling “sleep” mode) and both external wwwM.daOtaSsFhEeeTts4ua.croemturned off. The ITH pin is then disconnected from the output of the EA and “parked” at 0.425V. In sleep mode, much of the internal circuitry is turned off, reducing the quiescent current that the LTC3827-1 draws. If one channel is shut down and the other channel is in sleep mode, the LTC3827-1 draws only 80μA of quiescent current. If both channels are in sleep mode, the LTC3827-1 draws only 115μA of quiescent current. In sleep mode, the load current is supplied by the output capacitor. As the output voltage decreases, the EA’s output begins to rise. When the output voltage drops enough, the ITH pin is reconnected to the output of the EA, the sleep signal goes low, and the controller resumes normal operation by turning on the top external MOSFET on the next cycle of the internal oscillator. When a controller is enabled for Burst Mode operation, the inductor current is not allowed to reverse. The reverse current comparator (IR) turns off the bottom external MOSFET just before the inductor current reaches zero, preventing it from reversing and going negative. Thus, the controller operates in discontinuous operation. In forced continuous operation, the inductor current is allowed to reverse at light loads or under large transient conditions. The peak inductor current is determined by the voltage on the ITH pin, just as in normal operation. In this mode, the efﬁciency at light loads is lower than in Burst Mode operation. However, continuous has the advantages of lower output ripple and less interference to audio circuitry. In forced continuous mode, the output ripple is independent of load current. When the PLLIN/MODE pin is connected for pulse-skipping mode or clocked by an external clock source to use the phase-locked loop (see Frequency Selection and Phase- Locked Loop section), the LTC3827-1 operates in PWM pulse-skipping mode at light loads. In this mode, constant frequency operation is maintained down to approximately 1% of designed maximum output current. At very light loads, the current comparator ICMP may remain tripped for several cycles and force the external top MOSFET to stay off for the same number of cycles (i.e., skipping pulses). The inductor current is not allowed to reverse (discon- tinuous operation). This mode, like forced continuous operation, exhibits low output ripple as well as low audio noise and reduced RF interference as compared to Burst Mode operation. It provides higher low current efﬁciency than forced continuous mode, but not nearly as high as Burst Mode operation. Frequency Selection and Phase-Locked Loop (PLLLPF and PLLIN/MODE Pins) The selection of switching frequency is a tradeoff between efﬁciency and component size. Low frequency opera- tion increases efﬁciency by reducing MOSFET switching losses, but requires larger inductance and/or capacitance to maintain low output ripple voltage. The switching frequency of the LTC3827-1’s controllers can be selected using the PLLLPF pin. If the PLLIN/MODE pin is not being driven by an external clock source, the PLLLPF pin can be ﬂoated, tied to INTVCC, or tied to SGND to select 400kHz, 530kHz, or 250kHz, respectively. A phase-locked loop (PLL) is available on the LTC3827-1 to synchronize the internal oscillator to an external clock source that is connected to the PLLIN/MODE pin. In this case, a series R-C should be connected between the PLLLPF pin and SGND to serve as the PLL’s loop ﬁlter. The LTC3827-1 phase detector adjusts the voltage on the PLLLPF pin to align the turn-on of controller 1’s external top MOSFET to the rising edge of the synchronizing signal. Thus, the turn-on of controller 2’s external top MOSFET is 180 degrees out of phase to the rising edge of the external clock source. The typical capture range of the LTC3827-1’s phase-locked loop is from approximately 115kHz to 800kHz, with a guarantee over all manufacturing variations to be between 140kHz and 650kHz. In other words, the LTC3827-1’s PLL is guaranteed to lock to an external clock source whose frequency is between 140kHz and 650kHz. The typical input clock thresholds on the PLLIN/MODE pin are 1.6V (rising) and 1.2V (falling). 38271fe 11 11 Page

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