LTC4008 Linear Technology, LTC4008 Datasheet
LTC4008
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LTC4008 Summary of contents
Page 1
... An external resistor divider and precision internal reference set the final float voltage. The LTC4008 includes a thermistor sensor input that will suspend charging if an unsafe temperature condition is detected and will automatically resume charging when battery temperature returns to within safe limits; a FAULT pin indicates this condition ...
Page 2
... Charging Sum of Current from CLP, CLN, DCIN (Notes 2, 5) Measured from BAT to BATMON 100k LOAD V – V Target = 100mV CSP BAT DCIN = 0V (LTC4008 Only) ACP/SHDN = 0V DCIN Rising BAT V = 0V, Sum of Current from CLP, SHDN CLN, DCIN ORDER PART TOP VIEW DCIN ...
Page 3
... Input Bias Current BEA Sink Current OVSD Overvoltage Shutdown Threshold as a Percent of Programmed Charger Voltage Input P-Channel FET Driver (INFET) (LTC4008 Only) DCIN Detection Threshold (V Forward Regulation Voltage (V Reverse Voltage Turn-Off Voltage (V INFET “On” Clamping Voltage (V INFET “Off” Clamping Voltage (V ...
Page 4
... TGATE I = 1µA, DCIN = 0V, CLP = 12V BGATE Note 4: The LTC4008E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 5: Voltage accuracy includes BATMON error and voltage reference error ...
Page 5
... IN 0.150 0.125 0.100 0.075 0.050 0.025 –0.025 –0.050 –0.075 –0.100 –0.125 –0.150 1.50 2.00 2.50 3.00 4008 G10 LTC4008 (T = 25°C unless otherwise noted) A Disconnect/Reconnect Battery (Load Dump) 3A STEP 1A STEP V FLOAT 1V/(DIV) 3A STEP LOAD STATE DISCONNECT 0.8 0.9 1.0 LOAD CURRENT = 1A, 2A, 3A ...
Page 6
... Internal 10µA pull-up to 3.5V. The charger can also be shutdown by pulling this pin below 1V. The pin is capable of sinking at least 100µ external pull-up. (LTC4008-1: ACP function disabled.) R (Pin 4): Thermistor Clocking Resistor. Use a 150k T resistor as a nominal value. This resistor is always re- quired ...
Page 7
... CL 100mV 5k CLN + DCIN OSCILLATOR WATCHDOG 20µF DETECT t OFF CLP TGATE Q1 17 BGATE PWM Q2 19 LOGIC PGND 18 L1 *NOT USED IN THE LTC4008-1 – CLP CONTROL BLOCK + 1.19V Ω – Ω ÷ 5 – 1.28V CMP ...
Page 8
... LTC4008 TEST CIRCUIT 7 www.DataSheet4U.com U OPERATIO 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 ) from the PROG pin to ground PROG and a sense resistor (R ) between the CSP and BAT SENSE pins ...
Page 9
... ACP/SHDN pin is driven low and the charger is disabled. Input FET (LTC4008-1) The input FET circuit is disabled for the LTC4008-1. There is no low current shutdown mode when DCIN falls below the CLP pin. The ACP/SHDN pin functions only to shut down the charger. ...
Page 10
... Thermistor Detection 4008 F02 vs I CHARGE The thermistor detection circuit is shown in Figure 3. It requires an external resistor and capacitor in order to function properly 10k NTC voltage exceeds a threshold that assures TH LTC4008 R10 – 32.4k NTC 0.47µF + – – ...
Page 11
... T CLK (NOT TO SCALE) t HOLD VOLTAGE ACROSS THERMISTOR COMPARATOR HIGH LIMIT V NTC COMPARATOR LOW LIMIT Figure 4 LTC4008 = 10 • R • 17.5pF = 26µ 150k RT interval ends the result of the thermistor HOLD to zero and charging will BAD to one, the charger BAD returns to zero (see Figure 4). ...
Page 12
... Charging current can be programmed by pulse width modulating R with a switch PROG quency higher than a few kHz (Figure 5). C increased to reduce the ripple caused by the R switching. The compensation capacitor at I ably need to be increased also to improve stability and LTC4008 PROG 10 R PROG 5V Q1 2N7002 ...
Page 13
... Table 3 contains recom- mended values for R8 and R9 for popular float voltages Table 3 FLOAT VOLTAGE (V) Soft-Start The LTC4008 is soft started by the 0.12µF capacitor on the I pin. On start-up then ramp rate set by the internal 40µA pull-up C PROG 0.0047µ ...
Page 14
... LTC4008 U U APPLICATIO S I FOR ATIO 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 Appli- cation Note 88 for more information. Highest possible voltage rating on the capacitor will mini- mize problems ...
Page 15
... PD = 292mW vs DS(ON) Adapter Limiting = important feature of the LTC4008 is the ability to RSS GD automatically adjust charging current to a level which avoids overloading the wall adapter. This allows the prod- uct to operate at the same time that batteries are being charged without complex load management algorithms. ...
Page 16
... Figure 8. Unfortunately, since the HIGH/LOW comparator thresholds are fixed internally, there is only one thermistor type that can be used in this network; the thermistor must have a HIGH/LOW resis- tance ratio of 1:7. If this happy circumstance is true for you, then simply set LTC4008 R9 NTC ...
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... R ) TH(HIGH) TH(LOW) Example 24. 0.28µF → 0.27µF (nearest value) LTC4008 = 100k at 25°C, = 272.05k at 5°C = 33.195k at 50°C = 22k at 25°C, = 6.53k at 0°C = 61.4k at 50°C /(R9/7 • –ln(1 – 8 • 15mV/4.5V)) HOLD = 10 • R • 17.5pF/(R9/7 • – ln(1 – 8 • 15mV/4.5V) ...
Page 18
... SHDN pin only puts the charger into standby mode. Failure to isolate the battery power from ANY of the LTC4008-1 pins when wall adapter power is removed or lost will only drain the battery at the IC quiescent current rate. More specifically, high current is drawn from the DCIN, CLP and CLN pins ...
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... PGND R4 3.01k 1% R CSP T R5 3.01k 1% I BAT GND PROG 6.04k 150k 15k 28.7k 0.0047µF 0.12µF 0.25% 1% Figure 10. Typical LTC4008-1 Application (12.3V/4A) LTC4008 0.02Ω 4.99k 1% SYSTEM 1% LOAD C2 D2 20µF R SENSE L1 0.025Ω Q1 10µ 20µF Q5 ...
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... LTC4008 U U APPLICATIO S I FOR ATIO PCB Layout Considerations For maximum efficiency, the switch node rise and fall times should be minimized. To prevent magnetic and electrical field radiation and high frequency resonant prob- lems, proper layout of the components connected to the IC is essential. (See Figure 11.) Here is a PCB layout priority list for proper layout ...
Page 21
... For best current programming accuracy provide a Kelvin connection from R Figure example important to keep the parasitic capacitance on the R CSP and BAT pins to a minimum. The traces connecting these pins to their respective resistors should be as short as possible. LTC4008 to CSP and BAT. See SENSE , T 4008fa 21 ...
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... LTC4008 U U APPLICATIO S I FOR ATIO SWITCH NODE L1 HIGH FREQUENCY CIRCULATING PATH Figure 11. High Speed Switching Path DIRECTION OF CHARGING CURRENT R SENSE 4008 F12 CSP BAT Figure 12. Kelvin Sensing of Charging Current ...
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... BSC .015 ± .004 × 45° .0532 – .0688 (0.38 ± 0.10) (1.35 – 1.75) 0° – 8° TYP .008 – .012 (0.203 – 0.305) TYP INCHES LTC4008 .337 – .344* (8.560 – 8.738) .058 (1.473 REF .150 – ...
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... Linear Technology Corporation 24 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● U NiMH/4A Battery Charger Q3 INPUT SWITCH C1 0.1µF BATMON DCIN V INFET FB R1 4.99k 1% I LTC4008 CLP CL ACP/SHDN CLN FAULT TGATE FLAG BGATE NTC PGND R CSP T R4 3.01k 1% I BAT TH GND ...