LTC3545 LINER [Linear Technology], LTC3545 Datasheet
LTC3545
Available stocks
Related parts for LTC3545
LTC3545 Summary of contents
Page 1
... The internal synchronous switches increase effi ciency and eliminate external Schottky diodes. Low output voltages are supported with the 0.6V feedback reference voltage. The LTC3545-1 replaces the SYNC/MODE function with a third PGOOD pin and forces Burst Mode operation. C5 10μF ...
Page 2
... 3.6V unless otherwise noted. (Note CONDITIONS T = 25°C A 0°C ≤ T ≤ 85°C A LTC3545IUD; –40°C < T < 125° 2.25V to 5.5V IN TOP VIEW SW1 FB2 PGOOD1 2 ...
Page 3
... Continuous operation above the specifi ed maximum operating junction temperature may impair device reliability. Note 5: The LTC3545/LTC3545-1 are tested in a proprietary test mode that connects V to the output of the error amplifi er. ...
Page 4
... LTC3545/LTC3545-1 TYPICAL PERFORMANCE CHARACTERISTICS V vs Temperature at 2.25V, REF 3.6V, 5.5V 0.615 0.610 0.605 0.600 0.595 0.590 2.25V 3.6V 5.5V 0.585 – 100 TEMPERATURE (°C) 3545 G01 Burst Mode Operation SW 2V/DIV V OUT 20mV/DIV I L 100mA/DIV V = 3.6V 1μs/DIV 1.8V OUT I = 50mA LOAD f = 2.25MHz OSC 4 Switching Frequency vs Supply Voltage and Temperature 3 ...
Page 5
... I L 500mA/DIV I LOAD 500mA/DIV 3545 G10 T = 25°C 10μs/DIV 3. 1.5V OUT LOAD STEP 0mA TO 600mA Burst Mode OPERATION LTC3545/LTC3545-1 Effi ciency vs Load Current, Pulse Skipping Operation 100 25° 1.8V OUT CHANNEL 3, OTHER CHANNELS OFF ...
Page 6
... LTC3545/LTC3545-1 TYPICAL PERFORMANCE CHARACTERISTICS Start-Up From Shutdown Loaded V OUT1 V OUT2 V OUT3 (ALL 1V/DIV) RUNX 5V/DIV I SUPPLY 1A/DIV T = 25°C 200μs/DIV 3. 600mA, ALL CHANNELS LOAD PFET R vs Supply Voltage DS(ON) 0.60 0.50 0.40 0.30 0. 125° 80° 25°C 0. 0° –40°C ...
Page 7
... When driven by a 1MHz to 3MHz LTC3545/LTC3545-1 external clock, the part operates in pulse skipping mode with a switching frequency equal to the external clock. PGOOD3 (Pin 9, LTC3545-1 Only): This open-drain output voltage is pulled to a logic low when V is below (V is below 90% of regulated level). The LTC3545-1 ...
Page 8
... LTC3545/LTC3545-1 FUNCTIONAL DIAGRAMS RUN3 PGOOD3 (LTC3545-1 ONLY) SW3 POWER V FB3 REG3 PGOOD2 SW2 POWER V FB2 REG2 8 RUN2 V GNDA IN SHDN 0.6V OSC REF RUN LOGIC I BIAS3 I BIAS2 PV PGND IN SYNC/MODE RUN1 (LTC3545 ONLY) PGOOD1 I BIAS100 SW1 POWER V FB1 REG1 3545 FD01 35451fb ...
Page 9
... V FBX – 0.6V SOFT-START SHUTDOWN 0.6V V OSC REF BURST CLAMP SLOPE COMP – SLEEP SLEEP BURST LATCH R Q SWITCHING LOGIC AND BLANKING CIRCUIT OSC LTC3545/LTC3545-1 – + 10Ω I COMP ANTI SHOOT- THRU + I RCMP – 3545 FD02 PV IN SWX PGND 35451fb 9 ...
Page 10
... At very light loads, the LTC3545/LTC3545-1 will automati- cally begin operating in either pulse skipping or Burst Mode operation depending on the state of the MODE/SYNC pin (LTC3545). In either case the part will begin to skip cycles in order to maintain regulation. In pulse skip mode, the current pulses are smaller and more frequent, giving lower output ripple ...
Page 11
... An important detail to remember is that at low input supply voltages, the R increases (see Typical Performance Characteristics). Therefore, the user should calculate the power dissipation when the LTC3545/LTC3545-1 is used at 100% duty cycle with low input voltage (See Thermal Considerations in the Applications Information section). V ...
Page 12
... The choice of which style inductor to use often depends more on the price vs size requirements and any radiated fi eld/EMI requirements than on what the LTC3545/LTC3545-1 require to operate. Table 1 shows typical surface mount inductors that work well in LTC3545/LTC3545-1 applications. 12 Table 1 ...
Page 13
... The external resistive divider is connected to the output allowing remote voltage sensing as shown in Figure 2. = output capacitance Figure 2. Setting the LTC3545 Output Voltage Effi ciency Considerations The effi ciency of a switching regulator is equal to the output power divided by the input power times 100 often useful to analyze individual losses to determine what is limiting the effi ...
Page 14
... R where T is the ambient temperature. A )(1 – DC example, consider one channel of the LTC3545/ LTC3545-1 in dropout at an input voltage of 2.5V, a load current of 800mA, and an ambient temperature of 85°C. From the typical performance graph of switch resistance the R of the P-channel switch at 85°C can be es- DS(ON) timated as 0.42Ω ...
Page 15
... LOAD require a 250μs rise time, limiting the charging current to about 130mA. Design Example As a design example, consider using the LTC3545/LTC3545 portable application with a Li-Ion battery. The battery provides V one channel at 2.5V is 600mA. Using this channel as an example, fi rst calculate the inductor value for 40% ripple = ...
Page 16
... PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3545/LTC3545-1. These items are also illustrated graphically in Figures 3 and 4. Figure 3 shows the power path components and traces. In this fi gure the feedback networks are not shown since they reside on the bottom side of the board ...
Page 17
... PGND V FB3 RUN3 VIN 8 9 SW3 SYNC/MODE GND 17 V OUT3 AC COUPLED 20mV/DIV 250mA/DIV SW3 2V/DIV 1000 3545 TA03 Figure 4. LTC3545 Low Ripple Burst Mode Operation LTC3545/LTC3545-1 L1 1.5μ 10μF 20pF 191k 6.3V E4 GND R4 60.4k L2 1.5μ 10μF ...
Page 18
... LTC3545/LTC3545-1 TYPICAL APPLICATIONS R9 R2 511k 511k PGOOD3 PGOOD2 PGOOD1 V IN 2.5V TO 5.5V Figure 5. LTC3545-1 Three PGOODs and Power Sequencing 511k SW1 LTC3545-1 GNDA 2 15 PGOOD1 RUN2 RUN1 4 13 PGOOD2 V FB1 5 12 SW2 V FB2 6 11 PGND V FB3 RUN3 ...
Page 19
... Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. LTC3545/LTC3545-1 UD Package 16-Lead Plastic QFN (3mm 3mm) ...
Page 20
... LTC3545/LTC3545-1 RELATED PARTS PART NUMBER DESCRIPTION LTC3405/LTC3405A 300mA I , 1.5MHz, Synchronous Step-Down DC/DC OUT Converters LTC3406/LTC3406B 600mA I , 1.5MHz, Synchronous Step-Down DC/DC OUT Converters LTC3407/LTC3407-2 Dual 600mA/800mA I OUT Synchronous Step-Down DC/DC Converters LTC3409 600mA I , 1.7MHz/2.6MHz, Synchronous Step-Down OUT DC/DC Converter LTC3410/LTC3410B 300mA I , 2.25MHz, Synchronous Step-Down DC/DC OUT ...