Kan er iemand volgend schema ff overtekenen m.b.v een of ander CAD programma, aub?
Zodanig dat het een nette digitale voorstelling wordt.
Ik heb hier niet de juiste software voor staan.
Dank bij voorbaat!
Mvg,
FCBfreak
schema
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Mat Janssen
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Mat Janssen
- Moderator
- Berichten: 11595
- Lid geworden op: wo 10 dec 2003, 18:36
- Locatie: nederweert. .. .. .. .. .. .. .. .. .
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Stynus
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FCBfreak schreef:Heel erg bedankt!
Als je echt nog zin en tijd hebt, mag je de schakeling ook beschrijven!
EDIT: hier de werking nog:_______________General Description
The MAX856MAX859 are high-efficiency, CMOS, stepup,
DC-DC switching regulators for small, low input voltage
or battery-powered systems. The MAX856/MAX858
accept a positive input voltage between 0.8V and VOUT
and convert it to a higher, pin-selectable output voltage of
3.3V or 5V. The MAX857/MAX859 adjustable versions
accept 0.8V to 6.0V input voltages and generate higher
adjustable output voltages in the 2.7V to 6.0V range.
Typical efficiencies are greater than 85%. Typical quiescent
supply current is 25µA (1µA in shutdown).
The MAX856MAX859 combine ultra-low quiescent supply
current and high efficiency to give maximum battery life. An
internal MOSFET power transistor permits high switching
frequencies. This benefit, combined with internally set peak
inductor current limits, permits the use of small, low-cost
inductors. The MAX856/MAX857 have a 500mA peak
inductor current limit. The MAX858/MAX859 have a 125mA
peak inductor current limit
voor meer info zie de datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX856-MAX859.pdf_______________Detailed Description
Operating Principle
The MAX856MAX859 combine a switch-mode regulator,
N-channel power MOSFET, precision voltage reference,
and power-fail detector in a single monolithic
device. The MOSFET is a sense-FET type for best
efficiency, and has a very low gate threshold voltage to
ensure start-up with low battery voltages (0.8V typ).
PFM Control Scheme
A unique minimum-off-time, current-limited pulse-frequency
modulation (PFM) control scheme is a key feature
of the MAX856 series (Figure 1). This scheme
combines the high output power and efficiency of a
pulse-width modulation (PWM) device with the ultra-low
quiescent current of a traditional PFM pulse-skipper.
There is no oscillator; at heavy loads, switching is
accomplished through a constant-peak-current limit in
the switch, which allows the inductor current to vary
between this peak limit and some lesser value. At light
loads, switching frequency is governed by a pair of
one-shots, which set a minimum off-time (1µs) and a
maximum on-time (4µs). The switching frequency
depends upon the load and the input voltage, and can
range up to 500kHz.
The peak switch current of the internal MOSFET power
switch is fixed at 500mA ±100mA (MAX856/MAX857)
or 125mA ±25mA (MAX858/MAX859). The switchs onresistance
is typically 1½ (MAX856/MAX857) or 4½
(MAX858/MAX859), resulting in a switch voltage drop
(VSW) of about 500mV under high output loads. The
value of VSW will decrease with light current loads.
Conventional PWM converters generate constant-frequency
switching noise, whereas the unique architecture
of the MAX856MAX859 produces variable-frequency
switching noise. However, unlike conventional
pulse-skippers (where noise amplitude varies with input
voltage), noise in the MAX856 series does not exceed
the switch current limit times the filter-capacitor equivalent
series resistance (ESR).
Voltage Reference
The precision voltage reference is suitable for driving
external loads, such as an analog-to-digital converter.
The voltage-reference output changes less than ±2%
when sourcing up to 250µA and sinking up to 20µA. If
the reference drives an external load, bypass it with
0.22µF to GND. If the reference is unloaded, bypass it
with at least 0.1µF.