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LT3692A

3692afc

For more information www.linear.com/3692A

Typical applicaTion

FeaTures

applicaTions

DescripTion

Monolithic Dual Tracking

3.5A Step-Down Switching Regulator

The LT

3692A is a dual current mode PWM step-down

DC/DC converter with two internal 3.8A switches. Independent

input voltage, shutdown, feedback, soft-start, UVLO current

limit and comparator pins for each channel simplify complex

power supply tracking and sequencing requirements.

To optimize efficiency and component size, both convert

ers have a programmable maximum current limit and are

synchronized to either a common external clock input, or

resistor

settable fixed 250kHz to 2MHz internal oscillator.

A frequency divider is provided for channel 1 to further

optimize component size. At all frequencies, a 180° phase

relationship between channels is maintained, reducing volt

age ripple and component size. A clock output is available

for synchronizing multiple regulators.

Minimum input to output voltage ratios are improved by

allowing the switch to stay on through multiple clock cycles

only switching off when the boost capacitor needs recharg

ing. Independent channel operation can be programmed

using the SHDN pin. Disabling both converters reduces

the total quiescent current to <10µA.

The L

T3692A is an improved version of the L

T3692 with

reduced minimum on-time.

3.3V and 1.2V 2-Stage Dual Step-Down Multi-Frequency Converter

Wide Input Range:

– Operation from 3V to 36V

– OVLO Protects Circuit Through 60V Transients

Independent Supply, Shutdown, Soft-Start, UVLO,

Programmable Current Limit and Programmable

Power Good for Each 3.5A Regulator

Die Temperature Monitor

Adjustable/Synchronizable Fixed Frequency

Operation from 250kHz to 2MHz with Synchronized

Clock Output

Independent Synchronized Switching Frequencies

Optimize Component Size

Antiphase Switching

Outputs Can Be Paralleled

Flexible Output Voltage Tracking

Low Dropout: 95% Maximum Duty Cycle

5mm × 5mm QFN Package

FMEA Compliant 38-Pin Exposed Pad TSSOP Package

Automotive Supplies

Distributed Supply Regulation

Independent Synchronized Switching Frequencies

Extend Full Frequency Input Range

L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks

of Linear Technology Corporation. All other trademarks are the property of their respective owners.

BST1

SW1

OUT1

CMPI1

CMPO1

SS1

ILIM1

RT/SYNC

DIV

FB1

IND1

SW2

OUT2

CMPI2

CMPO2

SS2

ILIM2

CLKOUT

FB2

IND2

3692a TA01a

BST2

SHDN1 SHDN2

IN1

LT3692A

GND

IN2

4.7µF

IN1

5.5V TO 36V

OUT2

1.2V

2.2MHz

OUT1

3.3V

2.5A

550kHz

100k

4.7µH 0.5µH

0.22µF

0.1µF

100p

8.06k

102k13k100k

680pF33pF0.1µF

68.1k

220pF

0.1µF

22pF

33.2k40.2k

4.02k

FB1

10nF

CLKOUT

2.2MHz

8.06k

24.9k47µF

47µF

OUT1

3692a TA01c

CH1:

550kHz

CH2:

2.2MHz

= 30V

3692A TA01b

Summary of content (42 pages)

PAGE 1
LT3692A Monolithic Dual Tracking 3.5A Step-Down Switching Regulator Description Features n n n n n n n n n n n Wide Input Range: – Operation from 3V to 36V – OVLO Protects Circuit Through 60V Transients Independent Supply, Shutdown, Soft-Start, UVLO, Programmable Current Limit and Programmable Power Good for Each 3.
PAGE 2
LT3692A Absolute Maximum Ratings (Note 1) VIN1/2, SHDN1/2, CMPO1/2........................................40V VIN1/2 Transient (Note 2)............................................60V SW1/2.....................................................................VIN1/2 BST1/2.......................................................................60V BST1/2 Pin Above SW1/2...........................................25V IND1/2, VOUT1/2..........................................................
PAGE 3
LT3692A Order Information LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3692AEUH#PBF LT3692AEUH#TRPBF 3692A 32-Lead (5mm × 5mm) Plastic QFN –40°C to 125°C LT3692AIUH#PBF LT3692AIUH#TRPBF 3692A 32-Lead (5mm × 5mm) Plastic QFN –40°C to 125°C LT3692AHUH#PBF LT3692AHUH#TRPBF 3692A 32-Lead (5mm × 5mm) Plastic QFN –40°C to 150°C LT3692AEFE#PBF LT3692AEFE#TRPBF 3692AFE 38-Lead Plastic TSSOP –40°C to 125°C LT3692AIFE#PBF LT3692AIFE#TRPBF 3692AFE 38-
PAGE 4
LT3692A Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VVIN1/2 = 15V unless otherwise specified. (Note 3) PARAMETER CONDITIONS Soft-Start Source Current Ch 1/2 VFB1/2 = 2V, VSS1/2 = 0.07V Soft-Start VOH Ch 1/2 VFB1/2 = 2V l MIN TYP MAX UNITS 9.5 12 14.5 µA 1.9 2.15 2.4 V Soft-Start Sink Current Ch 1/2 VFB1/2 = 0.7V, VSS1/2 = 2V 0.7 1.
PAGE 5
LT3692A Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VVIN1/2 = 15V unless otherwise specified. (Note 3) PARAMETER CONDITIONS Minimum Boost for 100% DC Ch 1/2 (Note 9) IND + VOUT Current Ch 1/2 VVOUT1/2 = 0V VVOUT1/2 = 5V ILIM1/2 Reference Current VILIM = 0V IND to VOUT Maximum Current Ch 1/2 MIN TYP MAX 1.6 2.2 2.6 UNITS V 1.5 0.
PAGE 6
LT3692A Typical Performance Characteristics VIN Overvoltage Threshold vs Temperature Shutdown Threshold and Minimum Input Voltage vs Temperature 3.5 41.0 5000 40.0 2.5 39.5 2.0 SHUTDOWN THRESHOLD VOLTAGE 1.5 4000 39.0 IQ (µA) VOLTAGE (V) 38.5 38.0 37.0 0.5 1000 36.5 0 –50 –25 0 36.0 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 820 VSHDN1 = VSHDN2 = 0V CURRENT (µA) 5 4 3 2 815 0 –50 –25 6 1.25 4 1.
PAGE 7
LT3692A Typical Performance Characteristics Comparator Sink Current vs Temperature SINK CURRENT AT VCMPO = 0.4V 191 1400 FREQUENCY (kHz) 300 250 200 150 RRT/SYNC = 28.0k 1000 800 600 400 50 200 0 189 1200 100 0 –50 –25 RRT/SYNC = 13.
PAGE 8
LT3692A Typical Performance Characteristics Switch Peak Current vs Temperature 100 5.0 90 4.5 80 4.0 3A 60 50 40 30 10 0 2.50 VILIM = 0.5V 2.5 VILIM = 0V 2.0 1.5 0 –50 –25 0 1.00 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 0 25 50 75 100 125 150 TEMPERATURE (°C) 3692A G20 5.0V Efficiency and Power Loss 3.3V Efficiency and Power Loss 90 2500 2250 85 2000 EFFICIENCY 3.0 90 2.5 85 3.0 2.5 1500 1250 1000 750 500 80 2.0 75 70 1.
PAGE 9
LT3692A Pin Functions BST1/BST2: The BST pin provides a higher than VIN base drive to the power NPN to ensure a low switch drop. If the voltage between the BST pin and the VIN pin is less than the voltage required to fully turn on the power NPN, the power switch is turned off to recharge the BST capacitor. CMPI1/CMPI2: The CMPI pin is an input to a comparator with a threshold of 720mV and 60mV of hysteresis.
PAGE 10
LT3692A pin functions SHDN1/SHDN2: The shutdown pin is used to control each channel’s operation. In addition to controlling channel 1, the SHDN1 pin also activates control circuitry for both channels and must be present for channel 2 to operate. When SHDN1 is below its threshold, switching on both channels is halted. Further reducing the SHDN1 voltage to 0.
PAGE 11
LT3692A Block Diagram VIN1 1.32V SHDN1 + – + – VIN1 39V CHANNEL 1 THERMAL SHUTDOWN 2.5V 12µA SS1 S – + 90mV – + S PRE PRE Q R DROPOUT ENHANCEMENT BST1 DRIVER CIRCUITRY SW1 IND1 + – Q R VOUT1 VC1 R1 FB1 2.5V ILIM1 RLIM CMPI1 12µA SLOPE COMPENSATION 2.5V 2.5V DIV 0.806V 0.72V CMPO1 + – 12µA RT/SYNC R3 + + – R2 12µA OSCILLATOR AND AGC CLK1 VIN1 MASTER CLOCK 2.8V + – CLK2 TO CHANNEL 2 INTERNAL REGULATOR AND REFERENCES 2.5V TJ CLKOUT GND RDIV 3692a F01 Figure 1.
PAGE 12
LT3692A Applications Information during synchronization. In either mode of oscillator operation, a square wave with the master clock frequency, synchronized to channel 1 is present at the CLKOUT pin. The two regulators are constant frequency, current mode step-down converters. Current mode regulators are controlled by an internal clock and two feedback loops that control the duty cycle of the power switch.
PAGE 13
LT3692A Applications Information The voltage present at the TJ pin is proportional to the junction temperature of the LT3692A. The TJ pin will be 250mV for a die temperature of 25°C and will have a slope of 10mV/°C. Choosing the Output Voltage The output voltage is programmed with a resistor divider between the output and the FB pin. Choose the 1% resistors according to: V  R1= R2 •  OUT – 1  0.806  R2 should be 10k or less to avoid bias current errors.
PAGE 14
LT3692A Applications Information Table 2. Efficiency and Size Comparisons for Different RRT/SYNC Values, 3.3V Output FREQUENCY RT/SYNC EFFICIENCY VVIN1/2 = 12V VIN(MAX)† L* C* C + L (Area) 250kHz 5.90k 88% 39V 12µH 120µF 59.8mm2 500kHz 13.0k 87% 39V 5.6µH 60µF 54.6mm2 1000kHz 28.0k 84% 26V 3.3µH 30µF 51.9mm2 1500kHz 44.2k 82% 18V 1.5µH 22µF 46.9mm2 2250kHz 69.8k 78% 12V 1µH 15µF 19.
PAGE 15
LT3692A Applications Information The maximum input voltage is determined by the absolute maximum ratings of the VIN and BST pins and by the frequency and minimum duty cycle.
PAGE 16
LT3692A Applications Information can be set between 2A and 4.8A for each channel via a resistor from the ILIM pin to ground. The ILIM pin is driven by a 12µA current source. Setting resistor R LIM sets the voltage present at the ILIM pin which determines the maximum switch current as illustrated in Figure 6. A capacitor from the ILIM pin to ground, or a resistor divider from the output, can be used to limit the peak current during start-up.
PAGE 17
LT3692A Applications Information You can also use electrolytic capacitors. The ESRs of most aluminum electrolytics are too large to deliver low output ripple. Tantalum and newer, lower ESR organic electrolytic capacitors intended for power supply use, are suitable and the manufacturers will specify the ESR. The choice of capacitor value will be based on the ESR required for low ripple.
PAGE 18
LT3692A Applications Information D2 VIN VIN BST C3 D2 VIN SW VIN LT3692A GND (7b) D2 VX > VIN + 3V VIN BST C3 VIN SW VIN BST SW LT3692A LT3692A IND VOUT VBST – VSW = VX VBST(MAX) = VIN + VX VX(MIN) = 3V VOUT < 3V GND VBST – VSW = VIN VBST(MAX) = 2 • VIN D2 VIN SW IND VOUT VOUT (7a) VX = LOWEST VIN OR VOUT > 3V C3 LT3692A IND VOUT VBST – VSW = VOUT VBST(MAX) = VIN + VOUT BST IND VOUT VOUT < 3V GND VBST – VSW = VX VBST(MAX) = VX VX(MIN) = VIN + 3V (7c) VOUT < 3V GND 3692
PAGE 19
LT3692A Applications Information Loop compensation determines the stability and transient performance. Designing the compensation network is a bit complicated and the best values depend on the application and in particular the type of output capacitor. A practical approach is to start with one of the circuits in this data sheet that is similar to your application and tune the compensation network to optimize the performance.
PAGE 20
LT3692A Applications Information If the synchronization signal powers up in an undetermined state (VOL, VOH, Hi-Z), connect the synchronization clock to the LT3692A as shown in Figure 9. The circuit as shown will isolate the synchronization signal when the output voltage is below 90% of the regulated output. The LT3692A will start up with a switching frequency determined by the resistor from the RT/SYNC pin to ground.
PAGE 21
LT3692A Applications Information Reducing Input Ripple Voltage Shutdown and Undervoltage/Overvoltage Lockout Synchronizing the switches to the rising and falling edges of the synchronization signal provides the unique ability to reduce input ripple currents in systems where VIN1 and VIN2 are connected to the same supply. Decreasing the input current ripple reduces the required input capacitance. For example, the input ripple voltage shown in Figure 12 for a typical antiphase dual 14.4V to 8.5V and 14.
PAGE 22
LT3692A Applications Information Soft-Start The output of the LT3692A regulates to the lowest voltage present at either the SS pin or an internal 0.806V reference. A capacitor from the SS pin to ground is charged by an internal 12µA current source resulting in a linear output ramp from 0V to the regulated output whose duration is given by: tRAMP C • 0.806V = SS 12µA At power-up, a reset signal sets the soft-start latch and discharges both SS pins to approximately 0V to ensure proper start-up.
PAGE 23
LT3692A Applications Information Figure 14d illustrates output sequencing. When VOUT1 is within 10% of its regulated voltage, CMPO1 releases the SS2 soft-start pin allowing VOUT2 to soft-start. In this case CMPO1 will be pulled up to 2V by the SS pin. If a greater voltage is needed for CMPO1 logic, a pull-up resistor to VOUT1 can be used. This will decrease the soft-start ramp time and increase tolerance to momentary shorts.
PAGE 24
LT3692A Applications Information Independent Start-Up Ratiometric Start-Up Absolute Start-Up VOUT1 0.5V/DIV VOUT1 0.5V/DIV PG1 VOUT2 0.5V/DIV VOUT2 0.5V/DIV 5ms/DIV LT3692A FB1 CMPI1 0.72V + – 0.1µF CMPO1 12µA 0.72V + – FB1 CMPI1 2.5V 12µA 0.72V SS1 2.5V PG2 12µA 0.72V SS2 12µA PG1 0.72V + – R4 FB2 CMPI2 2.5V PG2 12µA 0.72V SS2 R8 0.22µF (14a) PG1 VOUT2 R6 R5 CMPO2 R3 R2 CMPO1 + – 0.1µF R4 FB2 CMPI2 FB1 CMPI1 2.
PAGE 25
LT3692A Applications Information VIN1 5.5V TO 36V 4.7µF 4.7µF VIN2 VIN1 SHDN1 BST1 VOUT1 1.2V 3A 300kHz 4.7µH 0.47µF SW1 SW2 IND1 IND2 4.7µH 0.47µF VOUT2 3.3V 2A 600kHz 100k LT3692A VOUT2 VOUT1 100µF ×3 8.06k 100k SHDN2 BST2 100pF 4.02k FB1 PG1 CMPI2 CMPO1 CMPO2 SS1 DIV 33pF 49.9k ILIM2 VC2 RT/SYNC 820pF 7.50k 15.8k 47µF 8.06k PG2 SS2 ILIM1 VC1 0.1µF 24.9k FB2 CMPI1 CLKOUT TJ GND ILIM1 CLOCKOUT 600kHz 680pF 33pF 10nF 61.9k 0.1µF 13.0k 3692a F15 Figure 15. 3.
PAGE 26
LT3692A Applications Information Shorted and Reverse Input Protection If the inductor is chosen so that it won’t saturate excessively, an LT3692A step-down regulator will tolerate a shorted output. There is another situation to consider in systems where the output will be held high when the input to the LT3692A is absent. This may occur in battery charging applications or in battery back-up systems where a battery or some other supply is diode OR-ed with the LT3692A’s output.
PAGE 27
LT3692A Applications Information PCB Layout For proper operation and minimum EMI, care must be taken during printed circuit board (PCB) layout. Figure 18 shows the high di/dt paths in the buck regulator circuit. Note that large switched currents flow in the power switch, the catch diode and the input capacitor. The loop formed by these components should be as small as possible.
PAGE 28
LT3692A Applications Information as heat sources. After the operating conditions have been determined, the individual power losses are calculated by:  V  PowerD1,2 = 1− OUT  •IOUT • VFD VIN   PowerIND1,2 = RIND •IOUT2 V PowerCH1,2 = 0.1• OUT •IOUT2 + 2•10 –3 VIN •VIN + IOUT • VOUT • VBOOST 40• VIN +  VIN IOUT  VIN •IOUT •FSW •10−6 •  +  0.3   3 where: FSW = Switching Frequency in kHz RIND = Inductor Resis tance VFD = Catch Diode Forward Voltage Drop VBOOST = Switch Boost Voltage Table 4.
PAGE 29
LT3692A Applications Information Die Temperature and Thermal Shutdown Generating a Negative Regulated Voltage The LT3692A TJ pin outputs a voltage proportional to the internal junction temperature. The TJ pin typically outputs 250mV for 25°C and has a slope of 10mV/°C. Without the aid of external circuitry, the TJ pin output is valid from 20°C to 150°C (200mV to 1.5V) with a maximum load of 100µA.
PAGE 30
LT3692A Applications Information CLKOUT Capacitive Loading A minor drawback to generating a negative rail from the CLKOUT pin is that the charge pump adds capacitance to the CLKOUT pin, resulting in an output synchronization clock signal phase delay. Figures 22 and 23 show the impact of capacitive loading on the CLKOUT signal rise and fall times.
PAGE 31
VIN 6V TO 36V For more information www.linear.com/3692A 0.1µF VOUT1 5V 1.5A 500kHz 100k 47µF 4.7µF 33pF 8.06k 680pF 10.0k 100pF 0.47µF 61.9k 42.2k 6.8µH VIN2 IND2 SW2 SHDN2 BST2 102k DIV GND TJ CLKOUT ILIM1 VC1 RT/SYNC SS2 ILIM2 VC2 SS1 CMPO2 CMPO1 FB2 CMPI2 CMPI1 FB1 LT3692A VOUT2 VOUT1 IND1 SW1 SHDN1 BST1 VIN1 10nF 16.9k 1.5µH 33pF 330pF 11.0k 8.06k 100pF 0.1µF 49.9k PG 100k 8.06k 10k CLOCKOUT 2MHz 22µF VOUT2 2.5V 1A 2MHz 8.06k 4.02k VOUT3 1.
PAGE 32
LT3692A TYPICAL APPLICATIONS 3.3V and 1.8V 2-Stage Dual Step-Down Multi-Frequency Converter VIN 5.5V TO 36V 4.7µF VIN2 VIN1 SHDN1 BST1 8.2µH 0.47µF VOUT1 3.3V 2.5A 400kHz 100µF SHDN2 BST2 SW1 SW2 IND1 IND2 100pF 24.9k FB1 FB2 CMPI1 CMPI2 CMPO1 CMPO2 SS1 DIV 33pF 16.5k ILIM2 VC2 RT/SYNC 470pF 47.5k 102k 10k 47µF 100pF 100k VOUT2 1.8V 1A 1600kHz 8.06k PG SS2 ILIM1 VC1 100k 0.22µF LT3692A VOUT2 VOUT1 8.06k 0.1µF 1µH CLKOUT GND TJ 0.
PAGE 33
LT3692A TYPICAL APPLICATIONS 12V to 3.3V and 2.5V Converter with Start-Up Current Limiting VIN 12V 4.7µF 4.7µF VIN2 VIN1 SHDN1 BST1 2.2µH 0.22µF VOUT1 2.5V 3A 1MHz SHDN2 BST2 SW1 SW2 IND1 IND2 0.22µF LT3692A VOUT2 VOUT1 47µF 8.06k 100pF 16.9k FB1 FB2 CMPI1 CMPI2 CMPO1 CMPO2 ILIM2 VC2 ILIM1 VC1 0.1µF RT/SYNC 330pF DIV 33pF 0.1µF 21.0k 28.0k 24.9k 100pF 8.06k 47µF VOUT2 3.3V 3A 1MHz SS2 SS1 120k 2.2µH CLKOUT GND TJ CLOCKOUT 1MHz 33pF 0.1µF 330pF 10nF 24.9k 0.
PAGE 34
LT3692A TYPICAL APPLICATIONS 3.3V/5A Single Output with UVLO/OVLO and Power Good VIN 5.5V TO 18V 60V TRANSIENT 4.7µF ×2 13k 174k 7.15k 37.4k SHDN2 BST1 CMPI2 CMPO2 51.1k ILIM1 ILIM2 820pF 33pF SW1 CLOCKOUT 1MHz SS1 VOUT2 SS2 VC1 BST2 SW2 CLKOUT 10nF 20k 28k DIV 47µF ×2 GND FB1 CMPI1 FB2 VOUT 3.3V 5A 2MHz EFFECTIVE RIPPLE 0.22µF 3.3µH IND2 RT/SYNC TJ 0.1µF 0.22µF 3.3µH IND1 LT3692A VOUT1 VC2 Q1 2N3904 34 VIN2 VIN1 SHDN1 24.9k 8.
PAGE 35
LT3692A TYPICAL APPLICATIONS Power Supply Dual Input Single 3.3V/4A Output Step-Down Converter VIN1 12V 4.7µF 47.5k 13k 2.2µF VIN2 VIN1 SHDN1 SHDN1 SHDN2 BST1 CMPO1 CMPO2 SW1 VIN2 5V 2A MAX 0.22µF 2.2µH IND1 LT3692A SS2 VOUT1 SS1 0.1µF 64.9k 36.5k 33pF 680pF 21.0k CLOCKOUT 2MHz 61.9k 61.9k ILIM1 VOUT2 ILIM2 VC1 BST2 SW2 VC2 0.22µF 2.2µH IND2 CLKOUT RT/SYNC DIV FB1 CMPI1 FB2 TJ CMPI2 10nF 47µF ×2 GND VOUT 3.3V 4A 24.9k 8.
PAGE 36
LT3692A TYPICAL APPLICATIONS 5V and 1.8V Dual 2-Stage Converter VIN1 6V TO 36V 4.7µF VIN2 VIN1 SHDN1 BST1 4.7µH 0.22µF VOUT1 5V 1A 1MHz SHDN2 BST2 SW1 SW2 IND1 IND2 1µH 0.22µF LT3692A VOUT2 VOUT1 22µF 100k 42.2k 8.06k PG FB1 CMPI2 CMPO1 CMPO2 SS1 0.1µF 49.9k 10k ILIM2 VC2 RT/SYNC DIV 33pF 61.9k 61.9k FB1 47µF 100pF 8.06k SS2 ILIM1 VC1 680pF 10k FB2 CMPI1 VOUT2 1.8V 1A 2MHz CLKOUT GND TJ ILIM1 CLOCKOUT 2MHz 33pF 0.1µF 330pF 10nF 39.
PAGE 37
100k 0.1µF PG1 VOUT1 12V 0.5A 1MHz 37.6k 33pF 470pF 8.06k 22µF 0.47µF VIN 15V TO 36V 28k 113k 1k 10µH OFF ON 4.7µF IND2 SW2 SHDN2 BST2 VIN2 FB2 DIV GND TJ CLKOUT ILIM2 VC2 ILIM1 VC1 RT/SYNC SS2 CMPO2 CMPI2 SS1 CMPO1 CMPI1 FB1 LT3692A VOUT2 VOUT1 IND1 SW1 SHDN1 BST1 VIN1 24.9k 10nF FB1 3.3µH SHDN1 33pF 16.0k 330pF 8.06k 0.22µF 100k 47µF For more information www.linear.com/3692A 133k 0.1µF 0.1µF SS2 VOUT3 1.
PAGE 38
LT3692A TYPICAL APPLICATIONS 5V, 3.3V, 2.5V, 1.8V Synchronized Quad Output VOUT1 5V 1A 2.2µF SVIN PVIN2 PVIN DDR 4.7µF ×2 RUN LT3612 MODE RT VIN2 VIN1 SHDN1 BST1 6.8µH 0.22µF 100pF 42.2k 8.06k SW1 SW2 IND1 IND2 FB1 FB2 CMPI1 CMPI2 CMPO1 SS1 CMPO2 SS2 ILIM2 VC2 ILIM1 VC1 0.1µF RT/SYNC 330pF DIV 33pF 60.4k 24.9k 16k 270k FB VOUT2 3.3V 100µF 2A ITH TRACK/SS SGND PGND SVIN PVIN2 60.4k SHDN2 BST2 6.8µH 2.2µF 0.22µF LT3692A VOUT2 VOUT1 47µF 3.
PAGE 39
LT3692A Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. FE Package 38-Lead Plastic TSSOP (4.4mm) (Reference LTC DWG # 05-08-1772 Rev C) Exposed Pad Variation AA 4.75 REF 38 9.60 – 9.80* (.378 – .386) 4.75 REF (.187) 20 6.60 ±0.10 4.50 REF 2.74 REF SEE NOTE 4 6.40 2.74 REF (.252) (.108) BSC 0.315 ±0.05 1.05 ±0.10 0.50 BSC RECOMMENDED SOLDER PAD LAYOUT 4.30 – 4.50* (.169 – .177) 0.09 – 0.20 (.0035 – .0079) 0.50 – 0.75 (.
PAGE 40
LT3692A 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 41
LT3692A Revision History REV DATE DESCRIPTION PAGE NUMBER A 9/11 Added H-grade 2 to 4 B 4/12 Clarified the synchronization maximum frequency and Typical Application. 1 Clarified the Electrical Characteristics table. 4 Clarified the DIV Voltage Threshold vs Temperature graph. 7 Replaced 90mV with 100mV. 12 Clarified Table 1. 13 Replaced DIV resistor values in the applications schematics.
PAGE 42
LT3692A Typical Application FMEA Fault Tolerant 3.3V/2A and 5V/2A Dual Converter VIN1 6V TO 36V (60V TRANSIENT) 4.7µF SHDN2 6.8µH 0.22µF VOUT1 5V 2A 500kHz VIN1 SHDN1 BST1 4.7µF 100k VIN2 SHDN2 BST2 SW1 SW2 IND1 IND2 5.6µH 0.22µF VOUT2 3.3V 2A 500kHz LT3692A VOUT2 VOUT1 4.22k 47µF 249k 806Ω PG1 SS2 ILIM2 FB1 CMPI2 CMPO1 CMPO2 SS1 820pF 12.7k 10nF ILIM1 VC1 DIV 100µF 806Ω 249k PG2 SS2 ILIM2 VC2 RT/SYNC 33pF 2.49k FB2 CMPI1 CLKOUT GND TJ CLOCKOUT 500kHz 13.