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参数资料
| 型号： | MAX1515ETG |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | Low-Voltage, Internal Switch, Step-Down/DDR Regulator |
| 中文描述： | 4.7 A SWITCHING REGULATOR, 1000 kHz SWITCHING FREQ-MAX, QCC24 |
| 封装： | 4 X 4 MM, 0.8 MM HEIGHT, MO-220-WGGD, TQFN-8 |
| 文件页数： | 16/24页 |
| 文件大小： | 504K |
| 代理商： | MAX1515ETG |
M
Low-Voltage, Internal Switch,
Step-Down/DDR Regulator
16
______________________________________________________________________________________
Pulse Skipping (Source Mode)
Connect
SKIP
to GND to allow the MAX1515 to auto-
matically switch between high-efficiency pulse-skipping
mode under light loads and PWM mode under heavy
loads. The transition from PWM mode to pulse-skipping
mode occurs when the load current is half the pulse-
skipping mode current threshold (800mA typ).
In pulse-skipping mode, the switching frequency is
reduced to increase efficiency. The inductor current is
discontinuous in this mode, and the MAX1515 only initi-
ates an LX switching cycle when V
FB
< V
REFIN
. When
V
FB
falls below V
REFIN
, the high-side NMOS switch
turns on and remains on until output is in regulation and
the current through the switch increases to the positive
pulse-skipping-mode current threshold (I
SKIP_P
) of
800mA. When the high-side NMOS switch turns off, the
low-side NMOS synchronous switch turns on and
remains on until the current through the switch decreas-
es to the zero-cross-current threshold of 200mA.
Pulse Skipping (Sink Mode)
When pulse-skipping operation is selected (
SKIP
=
GND) while in DDR mode (MODE = V
CC
), the
MAX1515’s source/sink controller switches operating
modes when the output voltage crosses either hys-
teretic sink/source thresholds (V
REFIN
±25mV). In
pulse-skipping source mode, the MAX1515 regulates
the valley of the output ripple voltage (see the
Pulse
Skipping (Source Mode)
section). When the output volt-
age rises above the sink-mode threshold, the MAX1515
enters sink mode. The MAX1515 begins each sink-
mode cycle by turning on the low-side NMOS. The low-
side NMOS remains on until the off-time (t
OFF
). After the
low-side NMOS turns off, the high-side NMOS turns on
and remains on until the current through the switch
reaches the zero-cross-current threshold of -350mA. As
long as the output voltage remains below the feedback
threshold, the controller remains in the high-impedance
state. Under light-load conditions, this allows the sink-
mode controller to automatically skip pulses. Under
heavy-load conditions, the output voltage remains
above the feedback threshold, forcing the sink-mode
controller to emulate typical forced-PWM operation.
The pulse-skipping current threshold allows the sink-
mode control scheme to automatically switch between
pulse-skipping PFM and nonskipping PWM operation.
This mechanism forces the boundary between continu-
ous and discontinuous inductor-current operation to be
half the negative pulse-skipping current threshold.
Output Voltage in Non-DDR Mode
In non-DDR mode (MODE = GND and V
REFIN
= V
REF
),
the output of the MAX1515 is selectable between one
of three preset output voltages: 2.5V, 1.8V, and 1.5V.
For a preset output voltage, connect FB to the output
voltage and connect FBSEL0 and FBSEL1 as indicated
in Table 4. For an adjustable output voltage, connect
FBSEL0 and FBSEL1 to GND and connect REFIN to a
Table 3. Modes of Operation
SHDN
MODE
PIN
SKIP
REFOUT
BUFFER
STEP-DOWN
REGULATOR MODE
STEP-DOWN
REGULATOR CURRENT
Low
Low
Low
High
X
X
Off, High-Z
On
Off
Off
Off
Off
High
Low
Low
Off, High-Z
On, non-DDR mode.
FB regulates to preset voltage or 0.5V.
Source only.
Pulse-skipping mode.
High
Low
High
Off, High-Z
On, non-DDR mode.
FB regulates to preset voltage or 0.5V.
Source/sink.
Forced-PWM mode.
High
High
Low
On
On, DDR mode.
FB regulates to REFIN.
Source/sink.
Pulse-skipping mode.
High
High
High
On
On, DDR mode.
FB regulates to REFIN.
Source/sink.
Forced-PWM mode.
Table 4. Output-Voltage Programming
FBSEL0
FBSEL1
OUTPUT
VOLTAGE
GND
GND
Adjustable
V
FB
= V
REFIN
1.5V
1.8V
2.5V
GND
V
CC
V
CC
V
CC
GND
V
CC
X = Don’t care.
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