Zakładka z wyszukiwarką danych komponentów |
|
ADP3000AR-12 Arkusz danych(PDF) 7 Page - Analog Devices |
|
ADP3000AR-12 Arkusz danych(HTML) 7 Page - Analog Devices |
7 / 12 page ADP3000 –7– REV. 0 Table II. Recommended Capacitors Vendor Series Type Phone Numbers AVX TPS Surface Mount (803) 448-9411 Sanyo OS-CON Through-Hole (619) 661-6835 Sprague 595D Surface Mount (603) 224-1961 Panasonic HFQ Through-Hole (201) 348-5200 DIODE SELECTION The ADP3000’s high switching speed demands the use of Schottky diodes. Suitable choices include the 1N5817, 1N5818, 1N5819, MBRS120LT3 and MBR0520LT1. Do not use fast recovery diodes because their high forward drop lowers effi- ciency. Neither general-purpose diodes nor small signal diodes should be used. PROGRAMMING THE SWITCHING CURRENT LIMIT OF THE POWER SWITCH The ADP3000’s RLIM pin permits the cycle by cycle switch current limit to be programmed with a single external resistor. This feature offers major advantages which ultimately decrease the component cost and P.C.B. real estate. First, it allows the ADP3000 to use low value, low saturation current and physi- cally small inductors. Additionally, it allows the ADP3000 to use a physically small surface mount tantalum capacitor with a typical ESR of 0.1 Ω to achieve an output ripple as low as 40 mV to 80 mV, as well as low input ripple. As a rule of thumb, the current limit is usually set to approximately 3 to 5 times the full load current for boost applications and about 1.5–3 times of the full load current in buck applications. The internal structure of the ILIM circuit is shown in Figure 17. Q1 is the ADP3000’s internal power switch, which is paralleled by sense transistor Q2. The relative sizes of Q1 and Q2 are scaled so that IQ2 is 0.5% of IQ1. Current flows to Q2 through both an internal 80 Ω resistor and the R LIM resistor. The voltage on these two resistors biases the base-emitter junction of the oscillator-disable transistor, Q3. When the voltage across R1 and RLIM exceeds 0.6 V, Q3 turns on and terminates the output pulse. If only the 80 Ω internal resistor is used (i.e. the I LIM pin is connected directly to VIN), the maximum switch current will be 1.5 A. Figure 8a gives values for lower current-limit values. VIN POWER SWITCH SW2 SW1 RLIM DRIVER 80 Ω (INTERNAL) ILIM IQ1 VIN 200 (EXTERNAL) Q2 ADP3000 Q1 400kHz OSC Q3 R1 Figure 17. ADP3000 Current Limit Operation The delay through the current limiting circuit is approximately 0.3 µs. If the switch ON time is reduced to less than 1.7 µs, accuracy of the current trip-point is reduced. Attempting to program a switch ON time of 0.3 µs or less will produce spurious responses in the switch ON time. However, the ADP3000 will still provide a properly regulated output voltage. PROGRAMMING THE GAIN BLOCK The gain block of the ADP3000 can be used as a low battery detector, error amplifier or linear post regulator. The gain block consists of an op amp with PNP inputs and an open-collector NPN output. The inverting input is internally connected to the ADP3000’s 1.245 V reference, while the noninverting input is available at the SET pin. The NPN output transistor will sink in excess of 300 µA. Figure 18 shows the gain block configured as a low battery monitor. Resistors R1 and R2 should be set to high values to reduce quiescent current, but not so high that bias current in the SET input causes large errors. A value of 33 k Ω for R2 is a good compromise. The value for R1 is then calculated from the formula: R1 = V LOBATT – 1.245 V 1.245 V R2 where VLOBATT is the desired low battery trip point. Since the gain block output is an open-collector NPN, a pull-up resistor should be connected to the positive logic power supply. ADP3000 1.245V REF GND AO 5V RL 47k Ω TO PROCESSOR R1 VBATT VIN SET RHYS R2 33k Ω 1.6M Ω VLB = BATTERY TRIP POINT R1 = VLB – 1.245V 37.7µA Figure 18. Setting the Low Battery Detector Trip Point |
Podobny numer części - ADP3000AR-12 |
|
Podobny opis - ADP3000AR-12 |
|
|
Link URL |
Polityka prywatności |
ALLDATASHEET.PL |
Czy Alldatasheet okazała się pomocna? [ DONATE ] |
O Alldatasheet | Reklama | Kontakt | Polityka prywatności | Linki | Lista producentów All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |