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LTC3890

3890fc

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

Selectable Current Limit

Very Low Dropout Operation: 99% Duty Cycle

Adjustable Output Voltage Soft-Start or Tracking

Power Good Output Voltage Monitors

Output Overvoltage Protection

Low Shutdown I

: < 14µA

Internal LDO Powers Gate Drive from V

or EXTV

No Current Foldback During Start-Up

Small Low Profile (0.75mm) 5mm × 5mm QFN Package

Automotive Always-On Systems

Battery Operated Digital Devices

Distributed DC Power Systems

Efficiency and Power Loss

vs Output Current

The LTC

3890 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 noise

due to the ESR of the input capacitor are minimized by

operating the two controller output stages out-of-phase.

The 50μA no-load quiescent current extends operating run

time 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

LTC3890 features a precision 0.8V reference and power

good output indicators. 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 leaded package version (28-lead Narrow

SSOP), see the LTC3890-1 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, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258,

7230497.

OUTPUT CURRENT (A)

EFFICIENCY (%)

POWER LOSS (mW)

100

10.10.010.0010.0001 10

3890 TA01b

20 1

100

1000

10000

0.1

= 12V

OUT

= 3.3V

0.1µF

100k

4.7µH

1000pF

470µF

22µF

0.008Ω

31.6k

34.8k

OUT1

3.3V

330µF

0.1µF

4.7µF

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

3890 TA01a

0.1µF

LTC3890

Downloaded from Arrow.com.

Summary of content (40 pages)

PAGE 1
LTC3890 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 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 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 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified 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 CONDITIONS IFB1,2 Feedback Current (Note 4) VREFLNREG Reference Voltage Line Regulation (Note 4) VIN = 4.5V to 60V VLOADREG Output Voltage Load Regulation (Note 4) Measured in Servo Loop, ∆ITH Voltage = 1.2V to 0.
PAGE 4
LTC3890 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the specified operating junction temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VRUN1,2 = 5V, EXTVCC = 0V unless otherwise noted.
PAGE 5
LTC3890 TYPICAL PERFORMANCE CHARACTERISTICS Efficiency and Power Loss vs Output Current VIN = 12V 90 VOUT = 3.3V Efficiency vs Output Current BURST EFFICIENCY 90 1000 CCM LOSS 100 60 40 BURST LOSS PULSE-SKIPPING LOSS 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 EFFICIENCY (%) 70 VOUT = 8.
PAGE 6
LTC3890 TYPICAL PERFORMANCE CHARACTERISTICS Total Input Supply Current vs Input Voltage VOUT = 3.3V FIGURE 13 CIRCUIT 200 300µA LOAD 150 100 NO LOAD 50 0 5.5 5.8 EXTVCC AND INTVCC VOLTAGE (V) SUPPLY CURRENT (µA) 250 5.6 5.0 5.4 INTVCC 5.2 5.0 EXTVCC RISING 4.8 EXTVCC FALLING 4.6 4.4 20 ILIM = GND ILIM = INTVCC 500 400 300 200 100 ILIM = FLOAT 0 FORCED CONTINUOUS MODE 0 0.2 0.4 0.6 0.8 VITH (V) 1.0 1.2 1.
PAGE 7
LTC3890 TYPICAL PERFORMANCE CHARACTERISTICS TRACK/SS Pull-Up Current vs Temperature Regulated Feedback Voltage vs Temperature Shutdown (RUN) Threshold vs Temperature 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 1.00 –75 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 300 200 100 VOUT < INTVCC – 0.5V 0 –100 –75 –50 –25 25 550 20 500 15 10 356 3.7 3.
PAGE 8
LTC3890 PIN FUNCTIONS SENSE1–, SENSE2– (Pin 1, Pin 9): The (–) Input to the Differential Current Comparators. When greater than INTVCC – 0.5V, the SENSE– pin supplies current to the current comparator. FREQ (Pin 2): The frequency control pin for the internal VCO. Connecting the pin to GND forces the VCO to a fixed low frequency of 350kHz. Connecting the pin to INTVCC forces the VCO to a fixed high frequency of 535kHz.
PAGE 9
LTC3890 PIN FUNCTIONS TG1, TG2 (Pin 26, Pin 15): High Current Gate Drives for Top N-Channel MOSFETs. These are the outputs of floating drivers with a voltage swing equal to INTVCC – 0.5V superimposed on the switch node voltage SW. PGOOD1, PGOOD2 (Pin 27, Pin 14): Open-Drain Logic Output. PGOOD1,2 is pulled to ground when the voltage on the VFB1,2 pin is not within ±10% of its set point. ILIM (Pin 28): Current Comparator Sense Voltage Range Inputs.
PAGE 10
LTC3890 FUNCTIONAL DIAGRAM VIN INTVCC PGOOD1 27 0.88V PHASMD CLKOUT 3 4 DUPLICATE FOR SECOND CONTROLLER CHANNEL VFB1 DROP OUT DET + – + – + PGOOD2 14 0.72V 0.88V VFB2 S Q R Q – BOT SWITCH LOGIC BOT SHDN INTVCC 0.72V – VCO CLK2 0.425V + ICMP PFD + SYNC DET + –+ +– – SLOPE COMP VFB 31, 11 + EA VIN – 22 – 20 7µA (RUN1) 0.5µA (RUN2) SHDN RST 2(VFB) 11V – 33 SGND 19 INTVCC 0.80V TRACK/SS + OV EXTVCC 5.
PAGE 11
LTC3890 OPERATION (Refer to the Functional Diagram) Main Control Loop The LTC3890 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 OPERATION (Refer to the Functional Diagram) Light Load Current Operation (Burst Mode Operation, Pulse-Skipping or Forced Continuous Mode) (PLLIN/MODE Pin) The LTC3890 can be enabled to enter high efficiency Burst Mode operation, constant frequency pulse-skipping mode, or forced continuous conduction mode at low load currents. To select Burst Mode operation, tie the PLLIN/ MODE pin to a DC voltage below 0.8V (e.g., SGND). To select forced continuous operation, tie the PLLIN/MODE pin to INTVCC.
PAGE 13
LTC3890 OPERATION (Refer to the Functional Diagram) A phase-locked loop (PLL) is available on the LTC3890 to synchronize the internal oscillator to an external clock source that is connected to the PLLIN/MODE pin. The LTC3890’s phase detector adjusts the voltage (through an internal lowpass filter) of the VCO input to align the turn-on of controller 1’s external top MOSFET to the rising edge of the synchronizing signal.
PAGE 14
LTC3890 OPERATION (Refer to the Functional Diagram) Figure 1 compares the input waveforms for a representative single-phase dual switching regulator to the LTC3890 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 APPLICATIONS INFORMATION The Typical Application on the first page is a basic LTC3890 application circuit. LTC3890 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 APPLICATIONS INFORMATION placed close to the switching node, to prevent noise from coupling into sensitive small-signal nodes. 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) determined by the ILIM setting.
PAGE 17
LTC3890 APPLICATIONS INFORMATION The equivalent resistance R1|| R2 is scaled to the room temperature inductance and maximum DCR: R1|| R2 = L (DCR at 20°C) • C1 The sense resistor values are: R1= R1|| R2 R1• RD ; R2 = RD 1– RD 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.
PAGE 18
LTC3890 APPLICATIONS INFORMATION The peak-to-peak drive levels are set by the INTVCC voltage. This voltage is typically 5.1V during start-up (see EXTVCC Pin Connection). Consequently, logic-level threshold MOSFETs must be used in most applications. Pay close attention to the BVDSS specification for the MOSFETs as well. Selection criteria for the power MOSFETs include the on-resistance, RDS(ON), Miller capacitance, CMILLER, input voltage and maximum output current.
PAGE 19
LTC3890 APPLICATIONS INFORMATION RMS capacitor current requirement. Increasing the output current drawn from the other controller will actually decrease the input RMS ripple current from its maximum value. The out-of-phase technique typically reduces the input capacitor’s RMS ripple current by a factor of 30% to 70% when compared to a single phase power supply solution. In continuous mode, the source current of the top MOSFET is a square wave of duty cycle (VOUT)/(VIN).
PAGE 20
LTC3890 APPLICATIONS INFORMATION Tracking and Soft-Start (TRACK/SS Pins) Soft-start is enabled by simply connecting a capacitor from the TRACK/SS pin to ground, as shown in Figure 6. An internal 1µA current source charges the capacitor, providing a linear ramping voltage at the TRACK/SS pin. The LTC3890 will regulate the VFB pin (and hence VOUT) according to the voltage on the TRACK/SS pin, allowing VOUT to rise smoothly from 0V to its final regulated value.
PAGE 21
LTC3890 APPLICATIONS INFORMATION INTVCC Regulators The LTC3890 features two separate internal P-channel low dropout linear regulators (LDO) that supply power at the INTVCC pin from either the VIN supply pin or the EXTVCC pin depending on the connection of the EXTVCC pin. INTVCC powers the gate drivers and much of the LTC3890’s internal circuitry. The VIN LDO and the EXTVCC LDO regulate INTVCC to 5.1V. Each of these can supply a peak current of 50mA and must be bypassed to ground with a minimum of 4.
PAGE 22
LTC3890 APPLICATIONS INFORMATION The following list summarizes the four possible connections for EXTVCC: 1. EXTVCC Grounded. This will cause INTVCC to be powered from the internal 5.1V regulator resulting in an efficiency penalty of up to 10% at high input voltages. 2. EXTVCC Connected Directly to VOUT . This is the normal connection for a 5V to 14V regulator and provides the highest efficiency. 3. EXTVCC Connected to an External Supply.
PAGE 23
LTC3890 APPLICATIONS INFORMATION Fault Conditions: Current Limit and Current Foldback Phase-Locked Loop and Frequency Synchronization The LTC3890 includes current foldback to help limit load current when the output is shorted to ground. If the output voltage falls below 70% of its nominal output level, then the maximum sense voltage is progressively lowered from 100% to 45% of its maximum selected value.
PAGE 24
LTC3890 APPLICATIONS INFORMATION Note that the LTC3890 can only be synchronized to an external clock whose frequency is within range of the LTC3890’s internal VCO, which is nominally 55kHz to 1MHz. This is guaranteed to be between 75kHz and 850kHz. Typically, the external clock (on the PLLIN/MODE pin) input high threshold is 1.6V, while the input low threshold is 1.1V. Rapid phase locking can be achieved by using the FREQ pin to set a free-running frequency near the desired synchronization frequency.
PAGE 25
LTC3890 APPLICATIONS INFORMATION Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: %Efficiency = 100% – (L1 + L2 + L3 + ...) where L1, L2, etc. are the individual losses as a percentage of input power.
PAGE 26
LTC3890 APPLICATIONS INFORMATION 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. When a load step occurs, VOUT shifts by an amount equal to ∆ILOAD (ESR), where ESR is the effective series resistance of COUT .
PAGE 27
LTC3890 APPLICATIONS INFORMATION Design Example As a design example for one channel, assume VIN = 12V (nominal), VIN = 22V (max), VOUT = 3.3V, IMAX = 5A, VSENSE(MAX) = 75mV and f = 350kHz. The inductance value is chosen first based on a 30% ripple current assumption. The highest value of ripple current occurs at the maximum input voltage. Tie the FREQ pin to GND, generating 350kHz operation. The minimum inductance for 30% ripple current is: ∆IL =  VOUT  V 1– OUT  ( f) (L)  VIN(NOM)  A 4.
PAGE 28
LTC3890 APPLICATIONS INFORMATION TRACK/SS1 ITH1 PGOOD2 VFB1 PGOOD1 RPU2 PGOOD2 VPULL-UP RPU1 VPULL-UP PGOOD1 R1* L1 SENSE1+ C1* SENSE1– SW1 LTC3890 FREQ BOOST1 PHASMD CLKOUT fIN PLLIN/MODE RUN1 CB1 M1 VIN CVIN PGND EXTVCC SENSE2– INTVCC SENSE2+ BG2 TRACK/SS2 1µF CERAMIC + CINTVCC D1* VIN M3 COUT1 + GND + CIN COUT2 1µF CERAMIC BOOST2 VFB2 ITH2 M2 RIN SGND R2* VOUT1 BG1 RUN2 C2* RSENSE TG1 M4 D2* CB2 SW2 RSENSE TG2 ILIM VOUT2 L2 3890 F11 *R1, R2, C1, C2,
PAGE 29
LTC3890 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 3890 F12 Figure 12. Branch Current Waveforms 3890fc 29 Downloaded from Arrow.com.
PAGE 30
LTC3890 APPLICATIONS INFORMATION PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the IC. These items are also illustrated graphically in the layout diagram of Figure 11. Figure 12 illustrates the current waveforms present in the various branches of the 2-phase synchronous regulators operating in the continuous mode. Check the following in your layout: 1.
PAGE 31
LTC3890 APPLICATIONS INFORMATION PC Board Layout Debugging Start with one controller on at a time. It is helpful to use a DC-50MHz current probe to monitor the current in the inductor while testing the circuit. Monitor the output switching node (SW pin) to synchronize the oscilloscope to the internal oscillator and probe the actual output voltage as well. Check for proper performance over the operating voltage and current range expected in the application.
PAGE 32
LTC3890 TYPICAL APPLICATIONS C1 1nF RB1 100k RA1 31.6k SENSE1+ INTVCC SENSE1– PGOOD1 VFB1 PGOOD2 CITH1A 100pF MBOT1 SW1 L1 4.7µH BOOST1 ITH1 CB1 0.1µF LTC3890 CSS1 0.01µF TRACK/SS1 TG1 ILIM PHSMD CLKOUT PLLIN/MODE VIN SGND EXTVCC RUN1 RUN2 FREQ VOUT2 RFREQ 41.2k CSS2 0.01µF TRACK/SS2 RITH2 34.8k CITH2 470pF 100k BG1 RITH1 34.8k CITH1 1000pF 100k ITH2 RA2 10.5k VFB2 RB2 100k RSENSE1 8mΩ VOUT1 3.3V 5A COUT1 470µF MTOP1 D1 INTVCC CINT 4.
PAGE 33
LTC3890 TYPICAL APPLICATIONS High Efficiency 8.5V Dual-Phase Step-Down Converter RB1 100k RA1 10.5k C1 1nF SENSE1+ INTVCC SENSE1– PGOOD1 VFB1 PGOOD2 CITH1A 100pF MBOT1 BG1 L1 8µH SW1 RITH1 34.8k LTC3890 INTVCC RMODE 100k TRACK/SS1 TG1 ILIM PHSMD CLKOUT PLLIN/MODE VIN SGND RRUN V 1000k OUT EXTVCC RUN1 RUN2 FREQ RFREQ 41.2k INTVCC VFB2 COUT1 330µF MTOP1 VIN CIN 9V TO 60V 220µF CINT 4.7µF PGND D2 TG2 BOOST2 ITH2 CB1 0.1µF D1 TRACK/SS2 CITH2 100pF VOUT1 8.
PAGE 34
LTC3890 TYPICAL APPLICATIONS High Efficiency Dual 12V/5V Step-Down Converter RB1 100k RA1 6.98k C1 1nF SENSE1+ INTVCC SENSE1– PGOOD1 VFB1 PGOOD2 CITH1A 100pF CITH1 470pF 100k BG1 RITH1 34.8k MBOT1 SW1 LTC3890 TRACK/SS1 ILIM PHSMD CLKOUT PLLIN/MODE SGND EXTVCC RUN1 RUN2 FREQ RFREQ 41.2k TG1 TRACK/SS2 CB1 0.47µF COUT1 180µF INTVCC CIN 220µF CINT 4.7µF PGND VOUT1 12V 3A MTOP1 VIN VIN 12.5V TO 60V D2 TG2 CB2 0.47µF BOOST2 MTOP2 L2 4.
PAGE 35
LTC3890 TYPICAL APPLICATIONS High Efficiency Dual 24V/5V Step-Down Converter RB1 487k C1 1nF CF1 33pF RA1 16.9k SENSE1– PGOOD1 100k 100k BG1 RITH1 46k MBOT1 L1 22µH RSENSE1 25mΩ SW1 TRACK/SS1 ILIM PHSMD CLKOUT PLLIN/MODE SGND EXTVCC RUN1 RUN2 FREQ CSS2 0.01µF TRACK/SS2 RITH2 20k ITH2 TG1 MTOP1 D1 VIN INTVCC CIN 220µF CINT 4.7µF PGND VIN 28V TO 60V D2 TG2 CB2 0.47µF BOOST2 MTOP2 L2 4.7µH SW2 BG2 RA2 18.7k COUT1 22µF ×2 CERAMIC CB1 0.
PAGE 36
LTC3890 TYPICAL APPLICATIONS 12V SEPIC and 3.3V Step-Down Converter INTVCC 1k L1 2k 2k VOUT1 6.8µF 0.1µF RB1 100k C1 1nF 511Ω RA1 6.98k PGOOD1 PGOOD2 SENSE1– BOOST1 CB1 0.1µF LTC3890 TRACK/SS1 INTVCC ILIM PHSMD CLKOUT PLLIN/MODE SGND VOUT1 EXTVCC RUN1 RUN2 FREQ RFREQ 41.2k CSS2 0.01µF TRACK/SS2 RITH2 7.15k COUT 68µF 6.8µF VOUT1 12V 2A RSNS1 6mΩ SW1 RMODE 100k D2 511Ω ITH1 CSS1 0.01µF CITH2 4.7nF M1 TG1 BG1 RITH1 12.1k 10µH 6.
PAGE 37
LTC3890 TYPICAL APPLICATIONS High Efficiency 12V at 25A Dual-Phase Step-Down Converter RB1 499k 10pF C1 1nF RA1 35.7k SENSE1– MBOT1 L1 10µH SW1 VOUT 12V 25A TRACK/SS1 SGND FREQ COUT1 150µF CB1 0.1µF LTC3890 RRUN1 1000k RSENSE1 3mΩ BOOST1 ITH1 CSS1 0.1µF ILIM PHSMD CLKOUT PLLIN/MODE VIN PGOOD1 BG1 RITH1 9.76k RFREQ 30.1k INTVCC 100k PGOOD2 VFB1 CITH1A 100pF CITH1 4.7nF SENSE1+ TG1 MTOP1 D1 VIN INTVCC CIN 100µF CINT 4.7µF PGND VIN 16V TO 60V D2 RUN1 RUN2 RRUN2 57.
PAGE 38
LTC3890 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UH Package 32-Lead Plastic QFN (5mm × 5mm) (Reference LTC DWG # 05-08-1693 Rev D) 0.70 ±0.05 5.50 ±0.05 4.10 ±0.05 3.50 REF (4 SIDES) 3.45 ± 0.05 3.45 ± 0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD 0.75 ± 0.05 R = 0.05 TYP 0.00 – 0.05 R = 0.
PAGE 39
LTC3890 REVISION HISTORY REV DATE DESCRIPTION PAGE NUMBER A 01/11 Added MP-grade and H-grade. Changes reflected throughout the data sheet. B 04/12 Clarified the Electrical Characteristics specifications. Added Typical Application schematics. C 10/12 Added INTVCC to Absolute Maximum Ratings 1-38 3, 36, 37 2 3890fc Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 40
LTC3890 TYPICAL APPLICATION High Efficiency Dual 12V/3.3V Step-Down Converter C1 1nF RB1 100k RA1 6.98k SENSE1+ INTVCC SENSE1– PGOOD1 VFB1 PGOOD2 CITH1A 100pF L1 8µH BOOST1 ITH1 CB1 0.47µF LTC3890 TRACK/SS1 ILIM PHSMD CLKOUT PLLIN/MODE SGND VOUT1 TG1 COUT1 180µF INTVCC CIN 220µF CINT 4.7µF VIN 12.5V TO 60V D2 TG2 TRACK/SS2 CB2 0.47µF BOOST2 MTOP2 L2 4.7µH SW2 RSENSE2 10mΩ ITH2 CITH2A 100pF VOUT1 12V 3A MTOP1 VIN CSS2 0.01µF RITH2 34.