Datenblatt-Suchmaschine für elektronische Bauteile |
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TC1142 Datenblatt(PDF) 6 Page - Microchip Technology |
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TC1142 Datenblatt(HTML) 6 Page - Microchip Technology |
6 / 12 page TC1142 DS21360B-page 6 2002 Microchip Technology Inc. 3.1 Output Voltage and Ripple For a -2x boost: In this case, the output voltage is given by: EQUATION 3-1: Here, f is the clock frequency and RS is the total ON resistance of the switches connecting C2 to GND and VOUT in phase 2 of the charge pump operating cycle with the equivalent series resistance (ESR) of C2. The output ripple voltage is given by: EQUATION 3-2: Here, ESR is the equivalent series resistance of COUT. In this case, the TC1142 is held in phase 2 until the output voltage drops below VR. When this occurs, the TC1142 reverts to phase 1 for a half period of the clock, during which C2 is charged from C1. At the end of this half-period, C2 is reconnected to COUT to boost the output voltage. During the phase 1 time period, the output voltage will drop below VR before it is boosted back, so the minimum output voltage is approximated by: EQUATION 3-3: The output ripple voltage is given approximately by: EQUATION 3-4: For values of VIN higher than |VR/2| by several hundred mV, the effect on ripple of the ESR of COUT can be neglected compared to the “overdrive” effect of VIN. Here, it can be seen that VRIPPLE increases with increasing VIN, but can be minimized by choosing small C1 and C2 values and a large COUT value. 3.2 Capacitor Selection To maintain low output impedance and ripple, it is recommended that capacitors with low equivalent series resistance (ESR) be used. Additionally, larger values of the output capacitor and smaller values of the flying capacitors will reduce output ripple. For a capacitor value of 4.7 µF for COUT, and values of 0.47 µF for C1 and C2, the typical output impedance of the TC1142 in regulation is 0.5 Ω. For the capacitor ESR not to have a noticeable effect on output impedance, it should not be larger than 1/2fCOUT. This also makes its effect on ripple voltage negligible. For VIN = 3.2V and VR = -5V, the output ripple voltage is less than 70 mVPP. Table 3-1 summarizes output ripple versus capacitor size for an input voltage of 3.2V and a regulated output voltage of -5V. Surface mount ceramic capacitors are preferred for their small size, low cost and low ESR. Low ESR tantalum capacitors also are acceptable. See Table 3-2 for a list of suggested capacitor suppliers. TABLE 3-1: VOLTAGE RIPPLE VS. C1/C2 FLYING CAPACITORS AND OUTPUT CAPACITOR COUT ESR = 0.1 Ω, IOUT = 20mA a.) For unregulated operation when VIN ≤ | |. 2 VR VOUT = -|2VIN| + IOROUT 1 1 1 RSC2 f C1 C2 (C2 + COUT) ) ( + + where ROUT = VRIPPLE = IORRIPPLE 1 1 ESR C2 2f(C2 + COUT) 2fCOUT (C2 + COUT) + + where RRIPPLE = b.) For regulated operation when VIN > | |. 2 VR VOUTMIN = -|VR| + IOROUT where ROUT = 1 ESR C2 2fCOUT (C2 + COUT) + VRIPPLE = (2VIN – |VR| + ESR IOC2 ) N + () C1 C2 1 1 1 1 C1 C2 ) ( + where N = (C2 + COUT) C1, C2 ( µF) COUT ( µF) VIN (V) VOUT (V) VRIPPLE (mV) 0.1 4.7 3.2 -5 14.6 0.22 4.7 3.2 -5 31.4 0.33 4.7 3.2 -5 46.1 0.47 4.7 3.2 -5 63.9 0.68 4.7 3.2 -5 88.7 1.0 4.7 3.2 -5 123.2 0.1 10 3.2 -5 7.0 0.22 10 3.2 -5 15.1 0.33 10 3.2 -5 22.4 0.47 10 3.2 -5 31.5 0.68 10 3.2 -5 44.7 1.0 10 3.2 -5 63.8 |
Ähnliche Teilenummer - TC1142 |
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Ähnliche Beschreibung - TC1142 |
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