Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - voltage regulators - DC DC switch controllers PolyPhase® SSOP 16

LTC3701

3701fa

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

2-Phase, Low Input Voltage,

Dual Step-Down DC/DC Controller

The LTC

3701 is a 2-phase dual constant frequency cur-

rent mode step-down DC/DC controller providing excellent

load and line regulation. Power loss and noise due to ESR

of the input capacitor are minimized by operating the two

controller output stages out-of-phase.

The LTC3701 provides a 0.8V ±2% voltage reference and

consumes only 460µA of quiescent current. To further

maximize the life of a battery source, the external

P-channel MOSFET is turned on continuously in dropout

(100% duty cycle).

Switching frequency is internally set at 550kHz, allowing

the use of small inductors and capacitors. For noise sen-

sitive applications, the LTC3701 can be externally syn-

chronized using its phase-locked loop. The frequency can

also be externally set from 300kHz to 750kHz by applying

a voltage to the PLLLPF pin. Burst Mode operation is inhib-

ited during synchronization or when the EXTCLK/MODE

pin is pulled low to reduce noise and RF interference.

The LTC3701 contains independent internal soft-start

circuitry for each controller. Other features include a

power good output voltage monitor and output overvolt-

age and short-circuit protection.

The LTC3701 is available in a small footprint 16-lead nar-

row SSOP package.

■

Out-of-Phase Controllers Reduce Required

Input Capacitance

■

True PLL for Frequency Locking or Frequency

Adjustment

■

Operating Frequency Range: 300kHz to 750kHz

■

Wide V

Range: 2.5V to 10V

■

Constant Frequency Current Mode Architecture

■

Low Dropout: 100% Duty Cycle

■

Power Good Output Voltage Monitor

■

Internal Soft-Start Circuitry

■

Selectable Burst Mode

/Pulse Skipping Operation

at Light Loads

■

Output Overvoltage Protection

■

Low Quiescent

Current: 460µA

■

0.8V ±2% Voltage Reference

■

Small 16-Lead Narrow SSOP Package

■

One or Two Lithium-Ion Powered Applications

■

Notebook and Handheld Computers

■

Personal Digital Assistants

■

Portable Instruments

■

Distributed DC Power Systems

Figure 1. High Efficiency 2-Phase 550kHz Dual Step-Down Converter

Efficiency vs Load Current

SENSE1

–

FB1

/RUN1

SGND

/RUN2

FB2

PLLLPF

SENSE2

–

SENSE1

PGATE1

PGND

PGATE2

PGOOD

EXTCLK/MODE

SENSE2

LTC3701

220pF

10k

D1, D2: IR10BQ015 L1, L2: LQN6C-4R7 M1, M2: FDC638P

78.7k

80.6k

100k

169k

4.7µH

47µF

10µF

47µF

0.03Ω

4.7µH

3701 F01a

OUT1

2.5V

2.5V TO 9.8V

OUT2

1.8V

, LTC and LT are registered trademarks of Linear Technology Corporation.

Burst Mode is a registered trademark of Linear Technology Corporation.

LOAD CURRENT (mA)

EFFICIENCY (%)

100

1 100 1000 10000

3701 F01b

= 3.3V

= 8.4V

OUT

= 2.5V

= 4.2V

= 6V

Summary of content (20 pages)

PAGE 1
LTC3701 2-Phase, Low Input Voltage, Dual Step-Down DC/DC Controller U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®3701 is a 2-phase dual constant frequency current mode step-down DC/DC controller providing excellent load and line regulation. Power loss and noise due to ESR of the input capacitor are minimized by operating the two controller output stages out-of-phase.
PAGE 2
LTC3701 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Input Supply Voltage (VIN)........................ – 0.3V to 10V SENSE1 –, SENSE2 –, PGATE1, PGATE2, PLLLPF, SENSE1+, SENSE2 +, EXTCLK/MODE Voltages .............. – 0.3V to (VIN + 0.3V) VFB1, VFB2, ITH/RUN1, ITH/RUN2 Voltages .................................. – 0.3V to 2.4V PGOOD Voltage ........................................ – 0.3V to 10V PGATE1, PGATE2 Peak Output Current (<10µs) .......
PAGE 3
LTC3701 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 4.2V unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS VPLLLPF = 1.2V or Floating VPLLLPF = 0V VPLLLPF ≥ 2.
PAGE 4
LTC3701 U W TYPICAL PERFOR A CE CHARACTERISTICS Undervoltage Lockout Trip Voltage (Falling) vs Temperature Undervoltage Lockout Trip Voltage (Rising) vs Temperature Maximum Current Sense Threshold vs Temperature MAXIMUM CURRENT SENSE THRESHOLD (mV) 2.20 2.15 2.18 2.16 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 2.10 2.05 2.00 1.95 2.14 2.12 2.10 2.08 2.06 2.04 1.90 2.02 1.85 –60 –40 –20 0 20 40 60 TEMPERATURE (°C) 80 100 2.
PAGE 5
LTC3701 U U U PI FU CTIO S SENSE1–, SENSE2– (Pins 1, 8): The (–) Inputs to the Differential Current Comparators. ITH/RUN1, ITH/RUN2 (Pins 2, 6): These pins each serve two functions. Each pin serves as the error amplifier compensation point as well as the run control input for the respective controller. Forcing one pin below 0.35V causes the functions associated with that controller to be shut down. Forcing both ITH/RUN pins below 0.35V causes the device to be shut down.
PAGE 6
LTC3701 W FU CTIO AL DIAGRA U U RSENSE1 L1 M1 VOUT VIN CIN SENSE1 + 15 VIN COUT D1 16 1 SENSE1 – SLOPE1 – CLK1 S ICMP VOLTAGE REFERENCE VREF 0.8V Q R + OV1 UV EXTCLK/MODE PLLLPF SCP – BURSTDIS PHASE DETECTOR 0.3V + – 0.5µA VFB1 R1 + – SLOPE COMP SLOPE1 VIN VREF 0.8V ITH/RUN1 SLOPE2 0.35V SHDN1 PGOOD1 PGOOD CLK1 100Ω 4 SGND 2 RC + VIN 11 3 EAMP CLK1 VOLTAGE CONTROLLED CLK2 OSCILLATOR CC 0.880V + SC1 10k RC 13 R2 CLOCK DETECT 7 – SLEEP1 0.
PAGE 7
LTC3701 U OPERATIO (Refer to Functional Diagram) Main Control Loop The LTC3701 uses a constant frequency, current mode architecture with the two controller channels operating 180 degrees out of phase. During normal operation, each external P-channel power MOSFET is turned on when the clock for that channel sets the RS latch, and turned off when the current comparator (ICMP) resets the latch.
PAGE 8
LTC3701 U OPERATIO (Refer to Functional Diagram) Dropout Operation Slope Compensation and Peak Inductor Current When the input supply voltage decreases towards the output voltage, the rate of change of the inductor current during the ON cycle decreases. This reduction means that the external P-channel MOSFET will remain on for more than one oscillator cycle if the inductor current has not ramped up to the threshold set by EAMP on the ITH/RUN pin.
PAGE 9
LTC3701 U OPERATIO (Refer to Functional Diagram) Why the need for 2-phase operation? Until recently, constant frequency dual switching regulators operated both channels in phase (i.e., single phase operation). This means that both topside MOSFETs are turned on at the same time, causing current pulses of up to twice the amplitude of those from a single regulator to be drawn from the input capacitor.
PAGE 10
LTC3701 U W U U APPLICATIO S I FOR ATIO The basic LTC3701 application circuit is shown in Figure␣ 1. External component selection is driven by the load requirement and begins with the selection of L and RSENSE. Next, the power MOSFET M1 and the output diode D1 are selected. Finally CIN (C1) and COUT (C2) are chosen. RSENSE Selection for Output Current RSENSE is chosen based on the required output current.
PAGE 11
LTC3701 U W U U APPLICATIO S I FOR ATIO size for a fixed inductor value, but is very dependent on the inductance selected. As inductance increases, core losses go down. Unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation.
PAGE 12
LTC3701 U W U U APPLICATIO S I FOR ATIO CIN and COUT Selection The selection of CIN is simplified by the 2-phase architecture and its impact on the worst-case RMS current drawn through the input network (battery/fuse/capacitor). It can be shown that the worst-case capacitor RMS current occurs when only one controller is operating. The controller with the highest (VOUT)(IOUT) product needs to be used in the formula below to determine the maximum RMS capacitor current requirement.
PAGE 13
LTC3701 U W U U APPLICATIO S I FOR ATIO error amplifier. The regulated output voltage is determined by:  R2  VOUT = 0.8 V •  1 +   R1 For most applications, an 80k resistor is suggested for R1. To prevent stray pickup, a 100pF capacitor is suggested across R1 close to the LTC3701. NORMALIZED VOLTAGE OR CURRENT (%) 105 100 95 VREF MAXIMUM OUTPUT CURRENT 90 85 80 75 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 INPUT VOLTAGE (V) 3701 F05 Figure 5.
PAGE 14
LTC3701 U W U U APPLICATIO S I FOR ATIO internal oscillator frequency may be set by applying a DC voltage to the PLLLPF pin. 550kHz operation can be selected by floating the PLLLPF pin. The PLLLPF pin may be connected to voltages as high as VIN. 2.4V RLP CLP EXTCLK/ MODE EXTERNAL OSCILLATOR PLLLPF DIGITAL PHASE/ FREQUENCY DETECTOR 10k OSCILLATOR 3701 F08 Figure 8. Phase-Locked Loop Block Diagram typically much larger than the DC supply current. In continuous mode, IGATECHG = f • QP.
PAGE 15
LTC3701 U W U U APPLICATIO S I FOR ATIO Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to (∆ILOAD)(ESR), where ESR is the effective series resistance of COUT. ∆ILOAD also begins to charge or discharge COUT, which generates a feedback error signal.
PAGE 16
LTC3701 U W U U APPLICATIO S I FOR ATIO 2) Are the signal and power grounds kept separate? The LTC3701 signal ground consists of the feedback resistor divider, the ITH/RUN compensation network, and Pin 4. The power ground consists of the (–) terminal of CIN, the (–) terminals of COUT1,2, the anodes of the Schottky diodes, and Pin 13 of the LTC3701. The power ground traces should be kept short, direct, and wide. Connect the anode of the Schottky diodes directly to the input capacitor ground.
PAGE 17
LTC3701 U W U U APPLICATIO S I FOR ATIO + COUT1 2 3 4 5 6 7 8 SENSE1 – SENSE1 ITH/RUN1 VIN VFB1 SGND + PGATE1 LTC3701 PGND VFB2 PGATE2 ITH/RUN2 PGOOD PLLLPF EXTCLK/MODE SENSE2 – M1 VOUT1 RSENSE1 16 15 D1 14 13 VIN + 12 CIN 11 10 9 SENSE2 + D2 L2 M2 + 1 – + L1 RSENSE2 COUT2 – + VOUT2 BOLD LINES INDICATE HIGH CURRENT PATHS 3701 F10 Figure 10.
PAGE 18
LTC3701 U TYPICAL APPLICATIO S 2-Phase, Synchronizable Dual Output Step-Down DC/DC Converter VIN 2.7V to 9.8V 1 R6 78.7k 2 R10 C6 220pF 10k 3 4 5 R5 10k C4 220pF R8 80k R9 100k 6 7 8 10k SENSE1 – SENSE1 + ITH/RUN1 VIN VFB1 SGND PGATE1 LTC3701 PGND VFB2 PGATE2 ITH/RUN2 PGOOD PLLLPF EXTCLK/MODE SENSE2 – SENSE2 + 16 M1 R1 0.03Ω 15 14 L1 4.7µH D1 VOUT1 2.5V 2A + C1 47µF GND 13 C2 10µF 12 100k 11 D2 VIN L2 4.7µH 10 9 C5 47µF VOUT2 1.8V 2A M2 R2 0.
PAGE 19
LTC3701 U TYPICAL APPLICATIO S 2-Phase, Synchronizable Dual Output Step-Down DC/DC Converter with 4A Output Currents 1nF R6 78.7k 1 2 R10 C6 220pF 10k 3 4 5 R8 80k R5 10k C4 220pF R9 100k 6 7 8 10k SENSE1 – SENSE1 + ITH/RUN1 VIN PGATE1 VFB1 SGND LTC3701 PGND VFB2 PGATE2 ITH/RUN2 PGOOD PLLLPF EXTCLK/MODE SENSE2 – SENSE2 + 16 15 R1 0.012Ω VIN 2.7V to 9.8V M1 L1 1.5µH 10Ω 14 13 D1 1µF + C1 47µF GND VOUT1 2.5V 4A C2 10µF 12 11 100k D2 VIN L2 1.5µH 10 9 R2 0.
PAGE 20
LTC3701 U TYPICAL APPLICATIO Dual Input Voltage Single Output, 2-Phase, 550kHz, Step-Down DC/DC Converter R7 169k 1 SENSE1 – 2 R6 78.7k R8 10k C5 220pF SENSE1 + ITH/RUN1 3 VIN VFB1 4 SGND 5 6 7 PGATE1 LTC3701 PGND VFB2 PGATE2 ITH/RUN2 PGOOD PLLLPF EXTCLK/MODE 8 SENSE2 – SENSE2 + 16 15 14 VIN1 2.5V TO 9.8V VIN1 ≥ VIN2 M1 R1 0.03Ω L1 4.7µH D1 + 13 VOUT 2.5V 2A C1 47µF C2 10µF 12 D2 11 10 9 L2 4.7µH R2 0.