LTC4008EGN Linear Technology, LTC4008EGN Datasheet

Page 1

... The I current is being reduced by input current limiting so that the charging algorithm can adapt. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and PowerPath and No R trademarks are the property of their respective owners. Protected by U.S. Patents including 5723970 ...

Page 2

... GN PACKAGE 20-LEAD NARROW PLASTIC SSOP = 125°C, θ 160°C/W JMAX JA EXPOSED PAD (PIN #) IS GND, MUST BE SOLDERED TO PCB *The LTC4008EGN-1 does not have the Input FET function ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL LTC4008EGN#PBF LTC4008EGN#TRPBF LTC4008EGN-1#PBF LTC4008EGN-1#TRPBF Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. ...

Page 3

ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T SYMBOL PARAMETER DCIN Operating Range I Operating Current Q V Voltage Accuracy TOL BATMON Error (Note 5) I Charge Current Accuracy (Note 3) TOL Shutdown Battery Leakage Current UVLO Undervoltage ...

Page 4

LTC4008 ELECTRICAL CHARACTERISTICS temperature range, otherwise specifi cations are at T SYMBOL PARAMETER Input P-Channel FET Driver (INFET) (LTC4008 Only) DCIN Detection Threshold (V – V DCIN Forward Regulation Voltage (V DCIN Reverse Voltage Turn-Off Voltage (V INFET “On” Clamping ...

Page 5

TYPICAL PERFORMANCE CHARACTERISTICS INFET Response Time to Reverse Current (REVERSE PFET (5A/DIV 1.25μs/DIV TEST PERFORMED ON DEMOBOARD V = 15VDC IN CHARGER = ON I ...

Page 6

LTC4008 TYPICAL PERFORMANCE CHARACTERISTICS Battery Leakage Current vs Battery Voltage 40 VDCIN = BATTERY VOLTAGE (V) Effi ciency at 12.6V with 15VDC V 100 ...

Page 7

PIN FUNCTIONS DCIN (Pin 1): External DC Power Source Input. Bypass this pin with at least 0.01μF. See Applications Information section. I (Pin 2): Input Current Limit Indicator. Active low CL digital output. Internal 10μA pull-up to 3.5V. Pulled low ...

Page 8

LTC4008 BLOCK DIAGRAM 0.1μF DCIN 5.8V INFET ACP/SHDN 3 FAULT 5 FLAG 14 GND 6 BATMON 13 1.19V CLP – 16 Ω 1.4m m 0.1μF R CL1 100mV CL ...

Page 9

TEST CIRCUIT BATMON 13 90.325k 9.675k OPERATION OVERVIEW The LTC4008 is a synchronous current mode PWM step down (buck) switcher battery charger controller. The charge current is programmed by the combination of a program resistor (R ) ...

Page 10

LTC4008 OPERATION Input FET (LTC4008) The input FET circuit performs two functions. It enables the charger if the input voltage is higher than the CLP pin and provides the logic indicator of AC present on the ACP/SHDN pin. It controls ...

Page 11

OPERATION 1.2 1.19V 1.0 0.8 0.6 0.4 0.309V 0 MAXIMUM CURRENT) CHARGE Figure PROG CHARGE If the charging current decreases below 10% to 15% of programmed current, while ...

Page 12

LTC4008 OPERATION The thermistor detector performs a sample-and-hold function. An internal clock, whose frequency is determined by the timing resistor connected to R closed to sample the thermistor 127.5 • 20 • R • 17.5pF = 6.7ms, SAMPLE ...

Page 13

APPLICATIONS INFORMATION Charger Current Programming The basic formula for charging current is: Ω V • REF = I CHARGE MAX ( ) R SENSE V = 1.19V. This leaves two degrees of freedom: R REF ...

Page 14

LTC4008 APPLICATIONS INFORMATION Battery Conditioning Some batteries require a small charging current to condi- tion them when they are severely depleted. The charging current is switched to a high rate after the battery voltage has reached a “safe” voltage to ...

Page 15

APPLICATIONS INFORMATION The relatively high ESR of an aluminum electrolytic for C1, located at the AC adapter input terminal, is helpful in reducing ringing during the hot-plug event. Refer to Application Note 88 for more information. Highest possible voltage rating ...

Page 16

LTC4008 APPLICATIONS INFORMATION Selection criteria for the power MOSFETs include the “ON” resistance R , total gate capacitance Q DS(ON) transfer capacitance C , input voltage and maximum RSS output current. The charger is operating in continuous mode so the ...

Page 17

APPLICATIONS INFORMATION used, with closed-loop feedback ensuring that adapter load current remains within limits. Amplifi er CL1 in Figure 7 senses the voltage across R , connected between the CL CLP and CLN pins. When this voltage exceeds 100mV, the ...

Page 18

LTC4008 APPLICATIONS INFORMATION LTC4008 R9 NTC 8 C7 R9A Figure 9. General Thermistor Network If you are using a thermistor that doesn’t have a 1:7 HIGH/LOW ratio, or you wish to set the HIGH/LOW limits to different temperatures, then the ...

Page 19

APPLICATIONS INFORMATION Disabling the Thermistor Function If the thermistor is not needed, connecting a resistor be- tween DCIN and NTC will disable it. The resistor should be sized to provide at least 10μA with the minimum voltage applied to DCIN ...

Page 20

LTC4008 APPLICATIONS INFORMATION DCIN 0V TO 28V V LOGIC R11 R12 100k 100k I CL FAULT FLAG 0.47μF 2N7002 THERMISTOR R9 R13 10k 15k 1.5k NTC 0.25% D1: MBRS130T3 D2: SBM540 Q1: Si4431BDY Q2: FDC645N Q4: Si7423DN ...

Page 21

APPLICATIONS INFORMATION PCB Layout Considerations For maximum effi ciency, the switch node rise and fall times should be minimized. To prevent magnetic and electrical fi eld radiation and high frequency resonant problems, proper layout of the components connected to the ...

Page 22

... FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 22 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. L1 ...

Page 23

REVISION HISTORY (Revision history begins at Rev B) REV DATE DESCRIPTION B 7/10 Updated Figure 5 and Figure 6. LTC4008 PAGE NUMBER 13, 14 4008fb 23 ...

Page 24

... D1: MBRS130T3 Q1: Si4431BDY Q2: FDC645N 4008 TA02 , Power Good Output, 3.5V ≤ V ≤ 36V IN and C , Uses Smallest Components for IN OUT OUT ≤ 2V, for Transmeta, AMD and Intel Mobile OUT LT 0710 REV B • PRINTED IN USA © LINEAR TECHNOLOGY CORPORATION 2003 NiMH BATTERY PACK 4008fb ...