LTC1649 Linear Technology, LTC1649 Datasheet
LTC1649
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LTC1649 Summary of contents
Page 1
... It operates from 2. input, and provides a regulated output voltage from 1.26V to 2. 20A load current. A typical 3.3V to 2.5V application features efficiency above 90% from 1A to 10A load. The LTC1649 uses a pair of standard 5V logic-level N-channel external MOSFETs, eliminating the need for expensive P-channel or super-low-threshold devices ...
Page 2
... Note 5: Under normal operating conditions, the charge pump will skip cycles to maintain regulation and the apparent frequency will be lower than 700kHz. Note 6: The I LIM (not current limited) operation, the INFORMATION ORDER PART TOP VIEW NUMBER VCC2 LTC1649CS MAX 11 COMP 10 CP OUT + 9 ...
Page 3
... LOAD CURRENT ( 100 1649 G01 100 60 80 1649 G03 1649 G06 LTC1649 Oscillator Frequency vs Temperature 240 230 220 210 200 190 180 170 – 40 – 100 TEMPERATURE ( C) 1649 G02 ...
Page 4
... OUT REF SHDN (Pin 5): Shutdown, Active Low. A TTL compatible LOW level at SHDN for more than 50 s puts the LTC1649 into shutdown mode. In shutdown, G1, G2, COMP and SS go low, and the quiescent current drops max. CP remains shutdown mode. A TTL compatible ...
Page 5
... VCC1 VCC2 LTC1649 I FB MAX SHDN COMP 1 F – GND CP OUT + 0 0.33 F MBR0530 Figure 1 LTC1649 – OUT PV CC1 G1 PV CC2 G2 MAX 40mV 1649 Q1 3300 F IRF7801 TWO IN L PARALLEL EXT 1 OUT 2. ...
Page 6
... Also included is an internal charge pump which provides 5V gate drive to the external MOSFETs with input supply voltage as low as 2.7V. The LTC1649 runs at an internally fixed 200kHz clock frequency and requires an external resistor divider to set the output voltage. ...
Page 7
... The LTC1649 is designed to operate from supplies as low as 2.7V while using standard 5V logic-level N-channel external MOSFETs. This poses somewhat of a challenge— from as little as 2.7V, the LTC1649 must provide signal to the lower MOSFET, Q2, while the upper MOSFET, Q1, requires a gate drive signal that swings from 5V) ...
Page 8
... TO-220 packages and heat sinks are not necessarily required in high efficiency applications. Siliconix Si4410DY and International Rectifier IRF7801 are two small, surface mount devices with R below with 5V of gate drive; both work well in LTC1649 circuits. A higher P MOSFET cost and circuit efficiency and increase MOSFET heat sink requirements. ...
Page 9
... ESR. During an output load transient, the output capacitor must supply all of the additional load current demanded by the load until the LTC1649 can adjust the inductor current to the new value. ESR in the output capacitor results in a step in the output voltage equal to the ESR value multiplied by the change in load current ...
Page 10
... F are typical filter values that work well in most applications. PV needs to be boosted to a level higher than CP CC1 provide gate drive to Q1. The LTC1649 initially used a charge pump from V cation uses a second charge pump to generate the PV supply. This second charge pump consists of a Schottky pin. This supply must ...
Page 11
... ESR will also help optimize output transient response. See Input and Output Capacitors for more information. Soft Start and Current Limit The LTC1649 includes a soft start circuit at the SS pin; this circuit is used both for initial start-up and during current error limit operation. SS requires an external capacitor to GND m with the value determined by the required soft start time ...
Page 12
... LTC1649 itself will drop below 25 A quiescent current typically, although off-state leakage in the external MOS- FETs may cause the total V higher, especially at elevated temperatures. When SHDN rises again, the LTC1649 will rerun a soft start cycle and , allowing it to pull SS LIM voltage in this condition from activating ...
Page 13
... As a general rule, power and signal grounds should be totally separated on the layout, and should be brought together 2 at only one point, right at the LTC1649 GND pin. This helps (1.265V) minimize internal ground disturbances in the LTC1649, while preventing excessive current flow from disrupting the operation of the circuits connected to GND ...
Page 14
... U U APPLICATIONS INFORMATION and output capacitors, the source of Q2, the LTC1649 GND pin, the output return and the input supply return all clustered at one point. Figure modified schematic showing the common connections in a proper layout. Note that at 10A current levels or above, current density in the PC board itself can become a concern ...
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... DWG # 05-08-1610 0.228 – 0.244 (5.791 – 6.197 0.053 – 0.069 (1.346 – 1.752) 0 – 8 TYP 0.014 – 0.019 (0.355 – 0.483) LTC1649 0.386 – 0.394* (9.804 – 10.008 0.150 – 0.157** (3.810 – 3.988) 3 ...
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... Pentium is a registered trademark of Intel Corporation. Linear Technology Corporation 16 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear-tech.com SSTL Logic Termination Supply V 3. CERAMIC P G1 VCC1 P I VCC2 LTC1649 MAX SHDN COMP CERAMIC – GND CP OUT + ...