LT1769 Linear Technology, LT1769 Datasheet
LT1769
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LT1769 Summary of contents
Page 1
... Charge current is reduced to keep the adapter current below specified levels. The LT1769 can charge batteries ranging from 1V to 20V. Ground sensing of current is not required and the battery’s negative terminal can be tied directly to ground. A saturat- ing switch running at 200kHz gives high charging effi- ciency and small inductor size ...
Page 2
... In Undervoltage State UVOUT UVOUT V 20V, V 0.4V BAT INFORMATION ORDER PART TOP VIEW NUMBER 1 28 GND GND** LT1769CGN 3 26 GND** LT1769IGN CC1 CC2 CC3 7 22 GND** *ALL V PINS SHOULD PROG BE CONNECTED TOGETHER CLOSE ...
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... PROG All Conditions < (Note 4) A All Conditions & < 0.45V C LT1769 = 200 (see Block Diagram), S3 MIN TYP MAX UNITS 0 0.15 0. mA/A 2 100 4 200 ...
Page 4
... LT1769 ELECTRICAL CHARACTERISTICS temperature range, otherwise specifications are at T PARAMETER Voltage Amplifier VA Transconductance (Note 3) Output Source Current OVP Input Bias Current Current Limit Amplifier CL1, 8V Input Common Mode Turn-On Threshold Transconductance CLP Input Current CLN Input Current Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired ...
Page 5
... G08 (Voltage Amplifier) VA OVP 125 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 I (mA) VA 1769 G05 V Pin Characteristics C 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 V (V) C 1769 G07 Reference Voltage vs Temperature 100 125 150 JUNCTION TEMPERATURE 1769 G09 LT1769 5 ...
Page 6
... LT1769 PIN FUNCTIONS GND (Pins 14, 15, 22 28): Ground Pins. Must be connected to expanded PC lands for proper heat sinking. See Applications Information section for details. SW (Pin 4): Switch Output. The Schottky catch diode must be placed with very short lead length in close proximity to SW pin and GND ...
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... GND – 75k 200kHz OSCILLATOR SHUTDOWN SLOPE COMPENSATION – – CA2 + V REF PROG I PROG C PROG R PROG LT1769 UV OUT V CC BOOST SPIN R S3 SENSE + CA1 R S2 BAT – I PROG + 0VP VA V REF – 2.465V g = 0.64 m 100mV ...
Page 8
... C 0.047 0.65V U OPERATION The LT1769 is a current mode PWM step-down (buck) switcher. The battery DC charge current is programmed by a resistor R (or a DAC output current) at the PROG PROG pin (see Block Diagram). Amplifier CA1 converts the charge current through much lower current I S1 fed into the PROG pin ...
Page 9
... If the ESR 0.2 and the battery impedance OUT is raised to 4 with a bead or inductor, only 5% of the ripple current will flow into the battery. Soft-Start and Undervoltage Lockout The LT1769 is soft-started by the 0.33 F capacitor on the V pin. On start-up, the V pin voltage will quickly rise ...
Page 10
... ADAPTER CURRENT LIMIT Figure 2. Adapter Input Current Limiting Adapter Current Limiting An important feature of the LT1769 is the ability to automatically adjust charge current to a level which avoids overloading the wall adapter. This allows the product to operate at the same time the batteries are being charged without complex load management algorithms ...
Page 11
... R3 2.465 390k Li-Ion batteries typically require float voltage accuracy 2%. Accuracy of the LT1769 OVP voltage is 0. and 1% over full temperature. This leads to the possibility that very accurate (0.1%) resistors might be needed for R3 and R4. Actually, the temperature of the LT1769 will rarely exceed float mode because charging currents have tapered off to a low level ...
Page 12
... PROG pin. 1769 F05 Thermal Calculations If the LT1769 is used for charging currents above 1A, a thermal calculation should be done to ensure that junction ) should S1 temperature will not exceed 125 C. Power dissipation in the IC is caused by bias and driver current, switch resis- tance and switch transition losses ...
Page 13
... SW 19 0.42 0.08 0.5W Total Power in the IC is: 0.35 + 0.43 + 0.5 = 1.3W Temperature rise will be (1.3W)(35 C/ This assumes that the LT1769 is properly heat sunk by con- necting the eleven fused ground pins to expanded traces and that the PC board has a backside or internal plane for heat spreading. The P term can be reduced by connecting the boost ...
Page 14
... The duty cycle can be extended to 93% by restricting boost voltage to 5V instead of using V is normally done. This lower boost voltage also reduces power dissipation in the LT1769 win-win deci- sion. Connect an external source Figure 10 with HIGH DUTY CYCLE CONNECTION ...
Page 15
... Contact Linear Technology for the LT1769 circuit PCB layout or Gerber file. D3 ADAPTER SYSTEM LOAD 1769 F12a LT1769 pin in the LT1769. When the input power is CC SWITCH NODE L1 HIGH FREQUENCY OUT CIRCULATING PATH Figure 13. High Speed Switching Path DS(ON) V ...
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... LT1769 U U APPLICATIONS INFORMATION NOTE: CONNECT ALL GND PINS TO EXPANDED PC LANDS FOR PROPER HEAT SINKING PACKAGE DESCRIPTION 0.015 0.004 0.053 – 0.069 45 (0.38 0.10) (1.351 – 1.748) 0.0075 – 0.0098 0 – 8 TYP (0.191 – 0.249) 0.016 – 0.050 0.008 – 0.012 (0.406 – 1.270) (0.203 – ...