LTC1879 LINER [Linear Technology], LTC1879 Datasheet
LTC1879
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LTC1879 Summary of contents
Page 1
... Operating supply current is only 15 A with no load and drops to < shutdown. The input supply voltage range of 2.65V to 10V makes the LTC1879 ideally suited for both single and dual Li-Ion battery-pow- ered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems ...
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... 0.7V, Duty Cycle < 10V 10V RUN INFORMATION ORDER PART TOP VIEW NUMBER 16 PLL_LPF LTC1879EGN 15 SYNC/MODE 14 PGOOD SWP2 GN PART 11 SWN2 MARKING 10 PGND2 9 PV IN2 1879 GN PACKAGE = 140 ...
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... Ramping Up RUN RUN Note 4: The LTC1879 is tested in a feedback loop which servos V balance point for the error amplifier (V Note 5: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency. Note 6: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction and power temperature will exceed 125 C when overtemperature protection is active ...
Page 4
... LTC1879 W U TYPICAL PERFOR A CE CHARACTERISTICS Switch Leakage vs Temperature 10V MAIN SWITCH SYNCHRONOUS 4 SWITCH 2 0 – 125 –25 100 TEMPERATURE ( C) 1879 G07 Reference Voltage vs Temperature 804 803 802 801 800 799 798 797 796 ...
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... 2. OUT OUT 50mA to 1200mA LOAD I 200mA/DIV V OUT 20mV/DIV SW 5V/DIV 1879 G18 LTC1879 Soft-Start with Shorted Output I VIN 500mA/DIV RUN/SS 1V/DIV 5ms/DIV OUT OUT LOAD Pulse Skipping Mode Operation L 2 ...
Page 6
... LTC1879 CTIO S SGND (Pin 1): Signal Ground Pin. RUN/SS (Pin 2): Combination of Soft-Start and Run Control Inputs. Forcing this pin below 0.7V shuts down the device. In shutdown all functions are disabled and device draws zero supply current. For the proper operation of the part, force this pin above 2 ...
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... W BLOCK DIAGRA LTC1879 1879f 7 ...
Page 8
... Note that there current flowing out of this pin. Soft-start action is accom- plished by connecting an external RC network to the RUN/ SS pin as shown in Figure 1. The LTC1879 actively pulls the RUN/SS pin to ground under low input supply voltage conditions. pin indicates a lower ...
Page 9
... Another important detail to remember is that at low input supply voltages, the R of the P-channel switch DS(ON) increases. Therefore, the user should calculate the power dissipation when the LTC1879 is used at 100% duty cycle with low supply voltage (see Thermal Considerations in the Applications Information section). 1800 1600 ...
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... Figure APPLICATIO S I FOR ATIO The basic LTC1879 application circuit is shown on the first page of this data sheet. External component selection is driven by the load requirement and begins with the selec- tion of L followed by C and C ...
Page 11
... L is highest at maximum input voltage since where IN OUT with input voltage. For the LTC1879, the general rule for proper operation is: ESR COUT The choice of using a smaller output capacitance in- creases the output ripple voltage due to the frequency dependent term but can be compensated for by using capacitor(s) of very low ESR to maintain low ripple volt- age ...
Page 12
... SGND Figure 4. Setting the LTC1879 Output Voltage Phase-Locked Loop and Frequency Synchronization The LTC1879 has an internal voltage-controlled oscillator and phase detector comprising a phase-locked loop. This allows the MOSFET turn- locked to the rising edge of an external frequency source. The frequency range of the voltage-controlled oscillator is 350kHz to 750kHz ...
Page 13
... But, in applications and Q are the gate B where the LTC1879 is running at high ambient tempera- ture with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction tempera- ...
Page 14
... DS(ON) usually necessary to iterate times through the equations to achieve a reasonably accurate value for the junction temperature example, consider the LTC1879 in dropout at an input voltage of 5V, a load current of 0.8A and an ambient temperature From the typical performance graph of switch resistance, the R of the P-channel switch DS(ON ...
Page 15
... For optimum load regulation and true sensing, the top of the output resistor divider should connect indepen- dently to the top of the output capacitor (Kelvin connec- tion), staying away from any high dV/dt traces. Place the divider resistors near the LTC1879 in order to keep the high impedance FB node short ...
Page 16
... LTC1879 U U APPLICATIO S I FOR ATIO Design Example As a design example, assume the LTC1879 is used in a dual lithium-ion battery-powered cellular phone applica- tion. The V will be operating from a maximum of 8.4V IN down to about 2.65V. The load current requirement is a maximum of 0.7A but most of the time it will be on standby mode, requiring only 2mA ...
Page 17
... PGND 5 LTC1879 L1 SWP SWP PLL_LPF 6 SWN 11 R1 SWN 887k 412k 1 SGND 100 2.5V OUT 0 100 OUTPUT CURRENT (mA) LTC1879 V IN 2.65V TO 8.4V C IN2 10 F GND C OUT OUT 2.5V 0.7A 1879 F09a 1000 1879 F09b 1879f 17 ...
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... THE MAXIMUM OUTPUT CURRENT OUT 18 R SVIN SYNC/MODE PGOOD IN1 PGND 2 RUN/SS 10 PGND 5 LTC1879 L1 SWP 8 SWP PLL_LPF 6 SWN 11 R1 SWN 523k 412k 1 SGND Efficiency vs Output Current 100 ...
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... TYP .015 .004 45 .053 – .068 (0.38 0.10) (1.351 – 1.727) 0 – 8 TYP .008 – .012 (0.203 – 0.305) LTC1879 .189 – .196* (4.801 – 4.978) .009 (0.229 REF .150 – .157** (3.810 – 3.988) ...
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... McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 R SVIN SYNC/MODE PGOOD IN1 PGND 2 RUN/SS 10 PGND L1 • 5 LTC1879 SWP SWP 16 4 PLL_LPF 6 SWN 11 R1 SWN 1. 412k 1 47pF SGND ...