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LM27951 Datasheet(PDF) 5 Page - Texas Instruments |
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LM27951 Datasheet(HTML) 5 Page - Texas Instruments |
5 / 20 page 5 LM27951 www.ti.com SNVS416C – NOVEMBER 2005 – REVISED FEBRUARY 2016 Product Folder Links: LM27951 Submit Documentation Feedback Copyright © 2005–2016, Texas Instruments Incorporated (1) All voltages are with respect to the potential at the GND pin. (2) CIN, COUT, C1, C2: Low-ESR surface-mount ceramic capacitors (MLCCs) used in setting electrical characteristics. (3) LED current matching is based on two calculations: [(IMAX – IAVG) / IAVG] and [(IAVG – IMIN) / IAVG]. IMAX and IMIN are the highest and lowest respective Dx currents, and IAVG is the average Dx current of all four current sources. The largest number of the two calculations (worst case) is considered the matching figure for the part. The typical specification provided is the most likely norm of the matching figure for all parts. (4) Headroom voltage (VHR) = VOUT − VDX. If headroom voltage requirement is not met, LED current regulation may be compromised. (5) EN logic input high current (IIH) is due to a 150-kΩ (typical) pulldown resistor connected internally between the EN and GND pins. (6) The open-loop output resistance (ROUT) models all voltage losses in the charge pump. ROUT can be used to estimate the voltage at the charge pump output VOUT and the maximum current capability of the device under low VIN and high IOUT conditions, beyond what is specified in the electrical specifications table: VOUT = (G × VIN) – (ROUT × IOUT). In the equation, G is the charge-pump-gain mode, and IOUT is the total output current (sum of all active Dx current sources and all current drawn from VOUT). 6.5 Electrical Characteristics Unless otherwise noted, typical limits are for TA = 25°C, and minimum and maximum limits apply over the full operating temperature (–40°C to +85°C); specifications apply to the Simplified Schematic with VIN = 3.6 V, V(EN) = 1.8 V, V(PWM) = 1.8 V, 4 LEDs, VDX = 3.6 V, CIN = COUT = 3.3 µF, C1 = C2 = 1 µF, RSET = 12.5 kΩ (1) (2). PARAMETER TEST CONDITIONS MIN TYP MAX UNIT IDX LED current regulation 3 V ≤ VIN ≤ 5.5 V RSET = 12.5 kΩ IVOUT = 0 mA 18.4 ( −8%) 20 21.6 (8%) mA 3 V ≤ VIN ≤ 5.5 V RSET = 8.32 kΩ IVOUT = 0 mA 30 3 V ≤ VIN ≤ 5.5 V RSET = 24.9 kΩ IVOUT = 0 mA 10 ID-MATCH LED current matching(3) RSET = 8.32 kΩ 0.2 1.5% IQ Quiescent supply current D(1-4) = OPEN RSET = OPEN 1.5 1.9 mA ISD Shutdown supply current 3 V ≤ VIN ≤ 5.5 V V(EN) = 0 V 0.1 1 µA VSET ISET pin voltage 3 V ≤ VIN ≤ 5.5 V 1.25 V IDX / ISET Output current to current set ratio 200 VHR Current source voltage headroom requirement(4) IDX = 95% IDX (nominal) RSET = 8.32 kΩ (IDX nominal = 30 mA) 360 mV IDX = 95% IDX (nom.) RSET = 12.5 kΩ (IDX nom. = 20 mA) 240 fSW Switching frequency 525 (–30%) 750 975 (30%) kHz VIH Logic input high Input pins: EN, PWM 3 V ≤ VIN ≤ 5.5 V 1 VIN V VIL Logic input low Input pins: EN, PWM 3 V ≤ VIN ≤ 5.5 V 0 0.4 IIH Logic input high current Input pin: PWM V(PWM) = 1.8 V 10 nA Input pin: EN V(EN) = 1.8 V(5) 12 µA IIL Logic input low current Input pins: EN, PWM V(EN, PWM) = 0 V 10 nA ROUT Charge pump output resistance (6) 3.3 Ω VGDX 1× to 3/2× gain transition voltage threshold on VDX (VOUT − VDX) Falling 500 mV tON Start-up time IDX = 90% steady state 330 µs |
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