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參數(shù)資料
| 型號(hào)： | DS1227 |
| 英文描述： | KickStarter Chip |
| 中文描述： | Kickstarter的芯片 |
| 文件頁數(shù)： | 9/20頁 |
| 文件大?。?/td> | 156K |
| 代理商： | DS1227 |
DS1227
022698 9/20
BOOST MODE OPERATION
The DS1227 Kickstarter incorporates all of the neces-
sary control and power switching functions required for
its +3V to +5V step-up DC-to-DC converter. These func-
tions include a bandgap reference, oscillator, voltage
comparator, catch diode and an N-channel MOSFET.
The only external components required are an output fil-
ter capacitor and a low cost inductor. The block diagram
shown in Figure 7 illustrates the DC-to-DC converter.
When kickstarting occurs from an initial powered down
state (i.e., V
CCO1
, V
CCO2
, and V
CCO3
turned off), an in-
ternal start sequence is initiated within the DS1227.
During this sequence, the V
CCO1
output remains shut
off and the BOOST pin is sampled in order to determine
if the DS1227 is configured for boost mode operation. If
BOOST is low, then boost mode operation is enabled
and the DC-to-DC converter is started.
The internal DC-to-DC converter is started by enabling
the on-chip 40 KHz oscillator. It then begins to build up
the voltage on the V
DCO
filter capacitor. Internal counter
logic insures that the DC-to-DC converter stays in start
mode for a minimum of six clock periods (nominally
150
μ
s @ 40 KHz). After this initial delay time, the V
DCO
output is monitored by the internal Error Comparator as
it slews up to V
DCON
. As long as the V
DCO
voltage re-
mains below the preset value, the Error Comparator will
be switched high and the internal 40 KHz oscillator will
be connected to the gate of the V
DCI
driver.
The V
DCI
driver is a large N-channel MOSFET with a
typical ON resistance of less than 4 Ohms and is capa-
ble of supplying a peak current of 450 mA. The output
device is turned on during each ON half-cycle gener-
ated by the internal square-wave oscillator, and is
turned off during each OFF half-cycle. During each ON
half-cycle, the current through the inductor rises linearly,
storing energy in the coil. When the output device is
turned off, the external inductor’s magnetic field col-
lapses, and the voltage across the inductor reverses
sign. The voltage at V
DCI
then rises until the internal
diode is forward biased, delivering power to the V
DCO
output. The converter is thereby powered from its own
V
DCO
output. This is often referred to as “bootstrapped”
operation, since the circuit figuratively “l(fā)ifts” itself up. In
order to guarantee that the Kickstarter can bootstrap it-
self up to operating voltage, the V
DCI
voltage must be at
the minimum level of V
DCISU
as listed in the DC charac-
teristics section of this data sheet.
When the voltage on V
DCO
rises to the V
DCON
thresh-
old, the internal signal called “HIENUF” will be active
and the V
CCO1
PMOS device is switched on. As noted
above, internal circuitry insures that this device will not
be switched on for a minimum of 6 clock cycles from the
time that the DC-to-DC converter is started. However,
since the recommended values for the external LC com-
ponents result in a time constant which is much longer
than six cycles, the actual slew rate will in practice be
much longer than this delay time.
If loading of the V
CCO
outputs causes V
DCO
to drop be-
low V
DCOFF
the DS1227 will deactivate HIENUF and
the V
CCO1
PMOS device as well as the other V
CCO
PMOS devices will be switched off. The V
DCO
voltage
will then be monitored for the V
DCON
trip point before re-
connecting the load. As a result, the power control regu-
lation loop could oscillate between these two states until
the V
CCO1
node had sufficient charge to remain above
the V
DCOFF
threshold. To prevent this from occurring,
the value of the filter capacitor must be sufficiently large.
For large capacitive loads on V
CCO1
the output may dip
below V
DCOFF
as a result of charge sharing and a larger
regulation capacitor at V
DCO
may be required. For large
resistive loads the inductance and capacitance values
may need to be adjusted using a smaller inductor value
and large capacitance. In order not to violate the peak
V
DCI
current it may be necessary to use the external os-
cillator OSCEXT to drive an additional switchmode
boost regulator, as shown in Figure 8.
Following the above described start sequence, normal
boost operation is performed by the converter. V
DCO
output voltage is constantly monitored by the error com-
parator. When V
DCO
voltage drops below the preset val-
ue, the error comparator switches high and connects
the internal 40 KHz oscillator to the gate of the V
DCI
out-
put driver. When the output voltage reaches the desired
level, the error comparator inhibits the V
DCI
output driv-
er until the load on V
CCO1
discharges the output filter ca-
pacitor to less than the desired output level.
INDUCTOR SELECTION
The available output current from the Kickstarter’s
on-chip DC-DC boost converter is a function of the input
voltage, external inductor value, output voltage and the
operating frequency. For most applications, the inductor
is the only design variable since the internal oscillator is
preset to a fixed value of 40 KHz. The proper inductor
must have the following characteristics:
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PDF描述 |
|---|---|
| DS1227S | KickStarter Chip |
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| DS1230W-100 | 3.3V 256k Nonvolatile SRAM |
| DS1233-10 | 5V EconoReset |
| DS1233Z-5 | 5V EconoReset |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| DS1227S | 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:KickStarter Chip |
| DS-1227ZJ | 制造商:Hikvision USA 功能描述:Flush Mount Bracket - Wht27In X 3.33In 制造商:HIKVISION 功能描述:FLUSH MOUNT BRACKET - WHT 27IN X 3.33IN |
| DS1228 | 制造商:DALLAS 制造商全稱:Dallas Semiconductor 功能描述:+5V Powered Dual RS-232 Transmitter/Receiver |
| DS-1229ZJ | 制造商:Hikvision USA 功能描述:Camera Wall Mount Bracket9.88In X 3.94In X 7.17In 制造商:HIKVISION 功能描述:CAMERA WALL MOUNT BRACKET 9.88IN X 3.94IN X 7.17IN |
| DS122E | 制造商:Miyama Electric 功能描述: |
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