Datasheet

ManualsBrandsLINEAR TECHNOLOGY ManualsPMICsPMIC - voltage regulators - DC DC switch controllers PolyPhase® SSOP 28

LTC3890-1

38901fb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

60V Low I

, Dual, 2-Phase

Synchronous Step-Down

DC/DC Controller

High Efficiency Dual 8.5V/3.3V Output Step-Down Converter

Wide V

Range: 4V to 60V (65V Abs Max)

Low Operating I

: 50µA (One Channel On)

Wide Output Voltage Range: 0.8V ≤ V

OUT

≤ 24V

SENSE

or DCR Current Sensing

Out-of-Phase Controllers Reduce Required Input

Capacitance and Power Supply Induced Noise

Phase-Lockable Frequency (75kHz to 850kHz)

Programmable Fixed Frequency (50kHz to 900kHz)

Selectable Continuous, Pulse-Skipping or Low Ripple

Burst Mode

Operation at Light Loads

Very Low Dropout Operation: 99% Duty Cycle

Adjustable Output Voltage Soft-Start or Tracking

Power Good Output Voltage Monitor

Output Overvoltage Protection

Low Shutdown I

: <14µA

Internal LDO Powers Gate Drive from V

or EXTV

No Current Foldback During Start-Up

Narrow SSOP Package

Automotive Always-On Systems

Battery Operated Digital Devices

Distributed DC Power Systems

Efficiency and Power Loss

vs Output Current

The LTC

3890-1 is a high performance dual step-down

switching regulator DC/DC controller that drives all

N-channel synchronous power MOSFET stages. A constant

frequency current mode architecture allows a phase-

lockable frequency of up to 850kHz. Power loss and supply

noise are minimized by operating the two controller output

stages out-of-phase.

The 50μA no-load quiescent current extends operating life

in battery-powered systems. OPTI-LOOP

compensation

allows the transient response to be optimized over a wide

range of output capacitance and ESR values. A wide 4V

to 60V input supply range encompasses a wide range of

intermediate bus voltages and battery chemistries.

Independent TRACK/SS pins for each controller ramp the

output voltages during start-up. Current foldback limits

MOSFET heat dissipation during short-circuit conditions.

The PLLIN/MODE pin selects among Burst Mode operation,

pulse-skipping mode, or continuous conduction mode at

light loads.

For a leadless 32-pin QFN package with additional features

of adjustable current limit, clock out, phase modulation

and two PGOOD outputs, see the LTC3890 data sheet.

L, LT, LTC, LTM, Linear Technology, Burst Mode, OPTI-LOOP and the Linear logo are

registered trademarks of Linear Technology Corporation. All other trademarks are the property

of their respective owners. Protected by U.S. Patents including 5481178, 5705919, 5929620,

6100678, 6144194, 6177787, 6304066, 6580258, 7230497.

0.1µF

100k

4.7µH

1000pF

470µF

4.7µF

22µF

0.008Ω

31.6k

34.8k

OUT1

3.3V

330µF

0.1µF

100k

8µH

1000pF

0.01Ω

10.5k

34.8k

OUT2

8.5V

TG1 TG2

BOOST1 BOOST2

SW1 SW2

BG1 BG2

SGND

PGND

SENSE1

SENSE2

SENSE1

–

SENSE2

–

FB1

FB2

ITH1 ITH2

INTV

TRACK/SS1 TRACK/SS2

9V TO 60V

38901 TA01a

0.1µF

LTC3890-1

OUTPUT CURRENT (A)

EFFICIENCY (%)

POWER LOSS (mW)

100

10.10.010.0010.0001 10

38901 TA01b

20 1

100

1000

10000

0.1

= 12V

OUT

= 3.3V

Summary of content (36 pages)

PAGE 1
LTC3890-1 60V Low IQ, Dual, 2-Phase Synchronous Step-Down DC/DC Controller DESCRIPTION FEATURES n n n n n n n n n n n n n n n n Wide VIN Range: 4V to 60V (65V Abs Max) Low Operating IQ: 50µA (One Channel On) Wide Output Voltage Range: 0.
PAGE 2
LTC3890-1 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION Input Supply Voltage (VIN).......................... –0.3V to 65V Topside Driver Voltages BOOST1, BOOST2 ...................................–0.3V to 71V Switch Voltage (SW1, SW2) .......................... –5V to 65V (BOOST1-SW1), (BOOST2-SW2) ................. –0.3V to 6V RUN1, RUN2 ................................................ –0.3V to 8V Maximum Current Sourced into Pin from Source >8V....................................................
PAGE 3
LTC3890-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VRUN1,2 = 5V, EXTVCC = 0V unless otherwise noted. (Note 2) SYMBOL PARAMETER VIN Input Supply Operating Voltage Range VFB1,2 Regulated Feedback Voltage CONDITIONS MIN TYP 4 ITH1,2 Voltage = 1.
PAGE 4
LTC3890-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VRUN1,2 = 5V, EXTVCC = 0V unless otherwise noted.
PAGE 5
LTC3890-1 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency and Power Loss vs Output Current VIN = 12V 90 VOUT = 3.3V Efficiency vs Output Current 10000 BURST EFFICIENCY 90 1000 CCM LOSS 100 60 50 BURST LOSS PULSE-SKIPPING LOSS 40 10 30 CCM EFFICIENCY 20 PULSE-SKIPPING EFFICIENCY 10 0 0.0001 0.001 0.01 0.1 1 OUTPUT CURRENT (A) FIGURE 13 CIRCUIT POWER LOSS (mW) 70 1 VOUT = 8.5V 98 VOUT = 3.
PAGE 6
LTC3890-1 TYPICAL PERFORMANCE CHARACTERISTICS Total Input Supply Current vs Input Voltage SUPPLY CURRENT (µA) 250 200 300µA LOAD 150 100 NO LOAD 50 0 5.5 5.6 5.0 5.4 INTVCC 5.2 5.0 EXTVCC RISING 4.8 EXTVCC FALLING 4.6 4.4 0 25 50 75 100 125 150 TEMPERATURE (°C) Burst Mode OPERATION 20 0 –20 0.4 0.6 0.8 VITH (V) 1.0 500 400 300 200 100 1.2 –100 1.
PAGE 7
LTC3890-1 TYPICAL PERFORMANCE CHARACTERISTICS TRACK/SS Pull-Up Current vs Temperature Regulated Feedback Voltage vs Temperature Shutdown (RUN) Threshold vs Temperature 1.40 808 1.05 RUN PIN VOLTAGE (V) TRACK/SS CURRENT (µA) 1.35 1.00 0.95 1.30 RUN1 RISING RUN2 RISING 1.25 1.20 1.15 RUN1 FALLING 1.10 RUN2 FALLING 1.05 0.90 –75 –50 –25 1.
PAGE 8
LTC3890-1 PIN FUNCTIONS ITH1, ITH2 (Pin 1, Pin 13): Error Amplifier Outputs and Switching Regulator Compensation Points. Each associated channel’s current comparator trip point increases with this control voltage. VFB1, VFB2 (Pin 2, Pin 12): Receives the remotely sensed feedback voltage for each controller from an external resistive divider across the output.
PAGE 9
LTC3890-1 PIN FUNCTIONS BG1, BG2 (Pin 23, Pin 18): High Current Gate Drives for Bottom (Synchronous) N-Channel MOSFETs. Voltage swing at these pins is from ground to INTVCC. PGOOD1 (Pin 27): Open-Drain Logic Output. PGOOD1 is pulled to ground when the voltage on the VFB1 pin is not within ±10% of its set point. BOOST1, BOOST2 (Pin 24, Pin 17): Bootstrapped Supplies to the Topside Floating Drivers.
PAGE 10
LTC3890-1 FUNCTIONAL DIAGRAM INTVCC DUPLICATE FOR SECOND CONTROLLER CHANNEL PGOOD1 BOOST DROP OUT DET 0.88V VFB1 + – + 0.72V S Q R Q TOP ON SWITCH LOGIC BOT INTVCC BG VOUT CLK2 0.425V – CLK1 + SLEEP – ICMP PFD + – CLP –+ +– + SYNC DET PLLIN/MODE IR – SENSE+ 2.7V 0.65V 100k SENSE– SLOPE COMP VFB VIN + EA – OV – 5.1V LDO EN LDO EN 7µA (RUN1) 0.5µA (RUN2) SHDN RST 2(VFB) + – 11V SGND INTVCC 0.80V TRACK/SS RB RA + EXTVCC 5.1V RSENSE L 3mV 4.
PAGE 11
LTC3890-1 OPERATION (Refer to the Functional Diagram) Main Control Loop The LTC3890-1 uses a constant frequency, current mode step-down architecture with the two controller channels operating 180 degrees out-of-phase. During normal operation, each external top MOSFET is turned on when the clock for that channel sets the RS latch, and is turned off when the main current comparator, ICMP, resets the RS latch.
PAGE 12
LTC3890-1 OPERATION (Refer to the Functional Diagram) Light Load Current Operation (Burst Mode Operation, Pulse-Skipping, or Forced Continuous Mode) (PLLIN/MODE Pin) just before the inductor current reaches zero, preventing it from reversing and going negative. Thus, the controller operates in discontinuous operation. The LTC3890-1 can be enabled to enter high efficiency Burst Mode operation, constant frequency pulse-skipping mode, or forced continuous conduction mode at low load currents.
PAGE 13
LTC3890-1 OPERATION (Refer to the Functional Diagram) If the PLLIN/MODE pin is not being driven by an external clock source, the FREQ pin can be tied to SGND, tied to INTVCC or programmed through an external resistor. Tying FREQ to SGND selects 350kHz while tying FREQ to INTVCC selects 535kHz. Placing a resistor between FREQ and SGND allows the frequency to be programmed between 50kHz and 900kHz, as shown in Figure 10.
PAGE 14
LTC3890-1 OPERATION (Refer to the Functional Diagram) Figure 1 compares the input waveforms for a representative single-phase dual switching regulator to the LTC3890-1 2-phase dual switching regulator. An actual measurement of the RMS input current under these conditions shows that 2-phase operation dropped the input current from 2.53ARMS to 1.55ARMS.
PAGE 15
LTC3890-1 APPLICATIONS INFORMATION The Typical Application on the first page is a basic LTC3890‑1 application circuit. LTC3890-1 can be configured to use either DCR (inductor resistance) sensing or low value resistor sensing. The choice between the two current sensing schemes is largely a design trade-off between cost, power consumption, and accuracy. DCR sensing is becoming popular because it saves expensive current sensing resistors and is more power efficient, especially in high current applications.
PAGE 16
LTC3890-1 APPLICATIONS INFORMATION Low Value Resistor Current Sensing A typical sensing circuit using a discrete resistor is shown in Figure 4a. RSENSE is chosen based on the required output current. The current comparator has a maximum threshold VSENSE(MAX). The current comparator threshold voltage sets the peak of the inductor current, yielding a maximum average output current, IMAX, equal to the peak value less half the peak-to-peak ripple current, ∆IL.
PAGE 17
LTC3890-1 APPLICATIONS INFORMATION The maximum power loss in R1 is related to duty cycle, and will occur in continuous mode at the maximum input voltage: PLOSS R1= ( VIN(MAX) – VOUT ) • VOUT R1 Ensure that R1 has a power rating higher than this value. If high efficiency is necessary at light loads, consider this power loss when deciding whether to use DCR sensing or sense resistors.
PAGE 18
LTC3890-1 APPLICATIONS INFORMATION usually provided on the MOSFET manufacturers’ data sheet. CMILLER is equal to the increase in gate charge along the horizontal axis while the curve is approximately flat divided by the specified change in VDS. This result is then multiplied by the ratio of the application applied VDS to the Gate charge curve specified VDS.
PAGE 19
LTC3890-1 APPLICATIONS INFORMATION offer much relief. Note that capacitor manufacturers’ ripple current ratings are often based on only 2000 hours of life. This makes it advisable to further derate the capacitor, or to choose a capacitor rated at a higher temperature than required. Several capacitors may be paralleled to meet size or height requirements in the design. Due to the high operating frequency of the LTC3890-1, ceramic capacitors can also be used for CIN.
PAGE 20
LTC3890-1 APPLICATIONS INFORMATION 1/2 LTC3890-1 TRACK/SS VX(MASTER) SGND 38901 F06 Figure 6. Using the TRACK/SS Pin to Program Soft-Start OUTPUT VOLTAGE CSS Alternatively, the TRACK/SS pin can be used to track two (or more) supplies during start-up, as shown qualitatively in Figures 7a and 7b. To do this, a resistor divider should be connected from the master supply (VX) to the TRACK/ SS pin of the slave supply (VOUT), as shown in Figure 8.
PAGE 21
LTC3890-1 APPLICATIONS INFORMATION pin is less than 4.7V, the VIN LDO is enabled. Power dissipation for the IC in this case is highest and is equal to VIN • IINTVCC. The gate charge current is dependent on operating frequency as discussed in the Efficiency Considerations section. The junction temperature can be estimated by using the equations given in Note 3 of the Electrical Characteristics.
PAGE 22
LTC3890-1 APPLICATIONS INFORMATION Topside MOSFET Driver Supply (CB, DB) External bootstrap capacitors, CB, connected to the BOOST pins supply the gate drive voltages for the topside MOSFETs. Capacitor CB in the Functional Diagram is charged though external diode DB from INTVCC when the SW pin is low. When one of the topside MOSFETs is to be turned on, the driver places the CB voltage across the gate-source of the desired MOSFET. This enhances the top MOSFET switch and turns it on.
PAGE 23
LTC3890-1 APPLICATIONS INFORMATION A shorted top MOSFET will result in a high current condition which will open the system fuse. The switching regulator will regulate properly with a leaky top MOSFET by altering the duty cycle to accommodate the leakage. 1000 900 FREQUENCY (kHz) 800 Phase-Locked Loop and Frequency Synchronization The LTC3890-1 has an internal phase-locked loop (PLL) comprised of a phase frequency detector, a lowpass filter, and a voltage-controlled oscillator (VCO).
PAGE 24
LTC3890-1 APPLICATIONS INFORMATION The minimum on-time for the LTC3890-1 is approximately 90ns. However, as the peak sense voltage decreases the minimum on-time gradually increases up to about TBDns. This is of particular concern in forced continuous applications with low ripple current at light loads. If the duty cycle drops below the minimum on-time limit in this situation, a significant amount of cycle skipping can occur with correspondingly larger current and voltage ripple.
PAGE 25
LTC3890-1 APPLICATIONS INFORMATION input capacitance requirement over competing solutions. Other losses including Schottky conduction losses during dead-time and inductor core losses generally account for less than 2% total additional loss. Checking Transient Response The regulator loop response can be checked by looking at the load current transient response. Switching regulators take several cycles to respond to a step in DC (resistive) load current.
PAGE 26
LTC3890-1 APPLICATIONS INFORMATION A 4.7µH inductor will produce 29% ripple current. The peak inductor current will be the maximum DC value plus one half the ripple current, or 5.73A. Increasing the ripple current will also help ensure that the minimum on-time of 95ns is not violated. The minimum on-time occurs at maximum VIN: VOUT 3.3V tON(MIN) = = = 429ns VIN(MAX) ( f) 22V (350kHz ) CIN is chosen for an RMS current rating of at least 3A at temperature assuming only this channel is on.
PAGE 27
LTC3890-1 APPLICATIONS INFORMATION 4. Are the SENSE– and SENSE+ leads routed together with minimum PC trace spacing? The filter capacitor between SENSE+ and SENSE– should be as close as possible to the IC. Ensure accurate current sensing with Kelvin connections at the SENSE resistor. 5. Is the INTVCC decoupling capacitor connected close to the IC, between the INTVCC and the power ground pins? This capacitor carries the MOSFET drivers’ current peaks.
PAGE 28
LTC3890-1 APPLICATIONS INFORMATION ITH1 TRACK/SS1 VFB1 PGOOD1 SENSE1 + TG1 SW1 SENSE1– LTC3890-1 BOOST1 FREQ fIN VPULL-UP PGOOD1 L1 R1* C1* RPU1 PLLIN/MODE RUN1 CB1 M1 C2* RIN VIN D1* CVIN 1µF CERAMIC COUT1 + PGND EXTVCC SENSE2– INTVCC SENSE2+ BG2 + CINTVCC VFB2 BOOST2 ITH2 SW2 VIN GND M3 + CIN COUT2 1µF CERAMIC R2* TRACK/SS2 VOUT1 BG1 RUN2 SGND M2 RSENSE M4 D2* CB2 RSENSE TG2 VOUT2 L2 38901 F11 *R1, R2, C1, C2, D1, D2 ARE OPTIONAL. Figure 11.
PAGE 29
LTC3890-1 APPLICATIONS INFORMATION SW1 L1 D1 RSENSE1 VOUT1 COUT1 RL1 VIN RIN CIN SW2 BOLD LINES INDICATE HIGH SWITCHING CURRENT. KEEP LINES TO A MINIMUM LENGTH. D2 L2 RSENSE2 VOUT2 COUT2 RL2 38901 F12 Figure 12.
PAGE 30
LTC3890-1 TYPICAL APPLICATIONS C1 1nF RB1 100k RA1 31.6k SENSE1+ INTVCC – SENSE1 PGOOD1 100k VFB1 CITH1A 100pF BG1 RITH1 34.8k CITH1 1000pF MBOT1 SW1 BOOST1 ITH1 LTC3890-1 CSS1 0.01µF L1 4.7µH TRACK/SS1 TG1 CB1 0.1µF RSENSE1 8mΩ VOUT1 3.3V 5A COUT1 470µF MTOP1 D1 VIN PLLIN/MODE SGND EXTVCC RUN1 RUN2 FREQ VOUT2 RFREQ 41.2k INTVCC D2 TG2 CSS2 0.01µF TRACK/SS2 RITH2 34.8k CITH2 470pF L2 8µH SW2 VFB2 RB2 100k MTOP2 CB2 0.1µF BOOST2 ITH2 RA2 10.5k CINT 4.
PAGE 31
LTC3890-1 TYPICAL APPLICATIONS High Efficiency 8.5V Dual-Phase Step-Down Converter RB1 100k RA1 10.5k C1 1nF SENSE1+ SENSE1– INTVCC PGOOD1 100k VFB1 MBOT1 CITH1A 100pF BG1 L1 8µH SW1 RITH1 34.8k CITH1 C SS1 0.01µF 470pF RSENSE1 10mΩ BOOST1 ITH1 LTC3890-1 TRACK/SS1 TG1 CB1 0.1µF VIN VIN CIN 9V TO 60V 220µF VIN PLLIN/MODE SGND RRUN V 1000k OUT EXTVCC RUN1 RUN2 FREQ RFREQ 41.2k INTVCC D2 TG2 TRACK/SS2 CITH2 100pF BOOST2 ITH2 VFB2 CINT 4.
PAGE 32
LTC3890-1 TYPICAL APPLICATIONS High Efficiency Dual 12V/5V Step-Down Converter RB1 100k RA1 6.98k C1 1nF SENSE1+ SENSE1– INTVCC PGOOD1 100k VFB1 CITH1A 100pF CITH1 470pF BG1 RITH1 34.8k MBOT1 SW1 LTC3890-1 CSS1 0.01µF L1 8µH BOOST1 ITH1 TRACK/SS1 TG1 CB1 0.47µF RSENSE1 9mΩ COUT1 180µF MTOP1 D1 VIN PLLIN/MODE SGND EXTVCC RUN1 RUN2 FREQ RFREQ 41.2k INTVCC TRACK/SS2 CITH2 470pF VIN 12.5V TO 60V D2 TG2 CSS2 0.01µF RITH2 20k CIN 220µF CINT 4.7µF PGND VOUT1 12V 3A CB2 0.
PAGE 33
LTC3890-1 TYPICAL APPLICATIONS High Efficiency Dual 24V/5V Step-Down Converter RB1 487k C1 1nF CF1 33pF RA1 16.9k SENSE1– INTVCC PGOOD1 100k VFB1 CITH1A 100pF CITH1 680pF SENSE1+ BG1 RITH1 46k MBOT1 L1 22µH RSENSE1 25mΩ SW1 BOOST1 ITH1 TRACK/SS1 COUT1 22µF ×2 CERAMIC CB1 0.47µF LTC3890-1 CSS1 0.01µF TG1 MTOP1 D1 VIN PLLIN/MODE SGND EXTVCC RUN1 RUN2 FREQ RFREQ 60k CSS2 0.01µF CITH2 470pF TRACK/SS2 RITH2 20k ITH2 INTVCC CIN 220µF CINT 4.7µF PGND VIN 28V TO 60V D2 TG2 CB2 0.
PAGE 34
LTC3890-1 PACKAGE DESCRIPTION GN Package 28-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .386 – .393* (9.804 – 9.982) .045 ±.005 28 27 26 25 24 23 22 21 20 19 18 17 1615 .254 MIN .033 (0.838) REF .150 – .165 .229 – .244 (5.817 – 6.198) .0165 ±.0015 .150 – .157** (3.810 – 3.988) .0250 BSC 1 RECOMMENDED SOLDER PAD LAYOUT .015 ± .004 × 45° (0.38 ± 0.10) .0075 – .0098 (0.19 – 0.25) 2 3 4 5 6 7 8 .0532 – .0688 (1.35 – 1.75) 9 10 11 12 13 14 .004 – .0098 (0.102 – 0.
PAGE 35
LTC3890-1 REVISION HISTORY REV DATE DESCRIPTION A 01/11 Added MP-grade and H-grade. Changes reflected throughout the data sheet. PAGE NUMBER B 10/12 Added INTVCC to Absolute Maximum Ratings 1-36 2 38901fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 36
LTC3890-1 TYPICAL APPLICATION High Efficiency Dual 12V/3.3V Step-Down Converter C1 1nF RB1 100k RA1 6.98k SENSE1+ SENSE1– INTVCC PGOOD1 100k VFB1 CITH1A 100pF BG1 RITH1 34.8k CITH1 470pF MBOT1 SW1 L1 8µH BOOST1 ITH1 CB1 0.47µF LTC3890-1 CSS1 0.01µF TRACK/SS1 TG1 RSENSE1 9mΩ COUT1 180µF MTOP1 D1 VIN PLLIN/MODE SGND VOUT1 RFREQ 41.2k EXTVCC RUN1 RUN2 FREQ INTVCC TRACK/SS2 RITH2 34.8k CB2 0.47µF BOOST2 MTOP2 L2 4.7µH SW2 RSENSE2 10mΩ ITH2 CITH2A 100pF VIN 12.