参数资料
型号: MAX668EUB+T
厂商: MAXIM INTEGRATED PRODUCTS INC
元件分类: 稳压器
英文描述: 1.8V to 28V Input, PWM Step-Up Controllers in µMAX
中文描述: SWITCHING CONTROLLER, 575 kHz SWITCHING FREQ-MAX, PDSO10
封装: COMPACT, UMAX-10
文件页数: 4/18页
文件大小: 289K
代理商: MAX668EUB+T
MAX668/MAX669
1.8V to 28V Input, PWM Step-Up
Controllers in MAX
12
______________________________________________________________________________________
Table 2. Bootstrapped and Non-Bootstrapped Configurations
CONFIGURATION
FIGURE
USE
WITH:
INPUT
VOLTAGE
RANGE* (V)
OUTPUT
VOLTAGE
RANGE (V)
COMMENTS
High-Voltage,
Bootstrapped
Figure
2
MAX669
1.8 to 28
3V to 28
Connect VCC to VOUT. Provides maximum external
FET gate drive for low-voltage (Input <3V) to high-
voltage (output >5.5V) boost circuits. VOUT cannot
exceed 28V.
Low-Voltage,
Bootstrapped
Figure
3
MAX669
1.8 to 5.5
2.7 to 5.5
Connect VOUT to VCC and LDO. Provides maxi-
mum possible external FET gate drive for low-volt-
age designs, but limits VOUT to 5.5V or less.
High-Voltage,
Non-Bootstrapped
Figure
4
MAX668
3 to 28
VIN to ∞
Connect VIN to VCC. Provides widest input and out-
put range, but external FET gate drive is reduced for
VIN below 5V.
Low-Voltage,
Non-Bootstrapped
Figure
5
MAX668
2.7 to 5.5
VIN to ∞
Connect VIN to VCC and LDO. FET gate-drive
amplitude = VIN for logic-supply (input 3V to 5.5V) to
high-voltage (output >5.5V) boost circuits. IC oper-
ating power is less than in Figure 4, since IC current
does not pass through the LDO regulator.
Extra IC supply,
Non-Bootstrapped
None
MAX668
Not
Restricted
VIN to ∞
Connect VCC and LDO to a separate supply
(VBIAS) that powers only the IC. FET gate-drive
amplitude = VBIAS. Input power source (VIN) and
output voltage range (VOUT) are not restricted,
except that VOUT must exceed VIN.
In addition to the configurations shown in Table 2, the
following guidelines may help when selecting a config-
uration:
1) If VIN is ever below 2.7V, VCC must be boot-
strapped to VOUT and the MAX669 must be used. If
VOUT never exceeds 5.5V, LDO may be shorted to
VCC and VOUT to eliminate the dropout voltage of
the LDO regulator.
2) If VIN is greater than 3V, VCC can be powered
from VIN, rather than from VOUT (non-bootstrapped).
This can save quiescent power consumption, espe-
cially when VOUT is large. If VIN never exceeds
5.5V, LDO may be shorted to VCC and VIN to elimi-
nate the dropout voltage of the LDO regulator.
3) If VIN is in the 3V to 4.5V range (i.e., 1-cell Li+ or
3-cell NiMH battery range), bootstrapping VCC from
VOUT, although not required, may increase overall
efficiency by increasing gate drive (and reducing
FET resistance) at the expense of quiescent power
consumption.
4) If VIN always exceeds 4.5V, VCC should be tied to
VIN, since bootstrapping from VOUT does not
increase gate drive from EXT but does increase
quiescent power dissipation.
*
For standard step-up DC-DC circuits (as in Figures 2, 3, 4, and 5), regulation cannot be maintained if VIN exceeds VOUT. SEPIC
and transformer-based circuits do not have this limitation.
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