参数资料
| 型号： | SC286ULTRT |
| 厂商： | Semtech |
| 文件页数： | 14/20页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ 4A 28MLPQ |
| 标准包装： | 1 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 0.8 V ~ 3.3 V |
| 输入电压： | 2.9 V ~ 5.5 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 1.6MHz |
| 电流 - 输出： | 4A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-UFQFN 裸露焊盘 |
| 包装： | 标准包装 |
| 供应商设备封装： | 28-MLPQ（4x4） |
| 其它名称： | SC286ULDKR |
SC286
Applications Information (continued)
VOUTA
LXB
Under this condition, the output voltage will be the product
of I CL_HOLD and the load resistance. When the load presented
falls below the current limit holding level, the output will
charge to the upper PSAVE voltage threshold and return to
normal operation. The SC286 is capable of sustaining an
indefinite short circuit without damage. During soft start, if
current limit has occurred before the SS voltage has reached
400mV, the part enters foldback current limit mode.
Foldback current limit mode will be disabled during soft-
start after the SS voltage is higher than 400mV.
Over-Voltage Protection
In the event of a 15% over-voltage on each independent
output, the PWM drive is disabled with the LX pin floating.
Switching does not resume until the output voltage falls
below the nominal V OUT regulation voltage.
V INA
V INB
C INA
22μF
C INB
22μF
R PGOODA
100k Ω
R PGOODA
100k Ω
Enable A
Enable B
R AVINA 1 Ω
C AVINA
0.1μF
R AVINB 1 Ω
C AVINB
0.1μF
PVINA LXA
SC286
AVINA
AGNDA
PGOODA
PVINB
AVINB
AGNDB
PGOODB
VOUTB
CTL0A
CTL1A
CTL2A
CTL3A
SSA
PGNDA
CTL0B
CTL1B
SSB
CTL2B
PGNDB
CTL3B
L
R FB1A
R FB2A
10k Ω
L
R FB1B
R FB2B
10k Ω
C SS
1nF
C SS
1nF
V OUTA
C FFA C OUTA
R FB1A = (V OUTA -1)
x R FB2A
for CTLA X = 0010
(1.0V)
V OUTB
C FFB C OUTB
R FB1B = (V OUTB -1)
x R FB2B
for CTLB X = 0010
(1.0V)
Programmable Output Voltage
The SC286 has fifteen pre-determined output voltage
Figure 2 — Output Voltage Programming
values which can be individually selected for each channel
by programming the CTL input pins (see Table 1 — Output
Voltage Settings). Each CTL pin has an active 500kΩ internal
R FB 1
V OUT V OSTD
V OSTD
R FB 2
pull-down resistor. The 500kΩ resistor is switched in circuit
whenever the CTL input voltage is below the input thresh-
old, or when the part is in under voltage lockout. It is
recommended to tie all high CTL pins together and use an
external pull-up resistor to AVIN if there is no enable signal
or if the enable input is an open drain/collector signal. The
CTL pins may be driven by a microprocessor to allow
where V OSTD is the pre-determined output voltage via the
CTL pins.
C FF is needed to maintain good transient response perfor-
mance. The correct value of C FF can be found using the
following equation.
dynamic voltage adjustment for systems that reduce the
supply voltage when entering sleep states. Avoid all zeros
being present on the CTL pins when changing program-
C FF [ nF ]
2 . 5
V OUT
R FB 1 [ k ]
0 . 5
V OUT
2
V OSTD
(
V OSTD
V OSTD 0 . 5
)
mable output voltages as this would disable the device.
SC286 is also capable of regulating a different (higher)
output voltage, which is not shown in the Table 1, via an
external resistor divider for each channel. There will be a
typical 2μA current flowing into the VOUTA/B pin. The
typical schematic for an adjustable output voltage option
from the standard 1.0V with CTL XA/B = [0010], is shown in
Figure 2. RFB1A/B and RFB2A/B are used to adjust the
desired output voltage. If the RFB2A/B current is such that
the 2μA VOUTA/B pin current can be ignored, then RFB1A/
B can be found using the next equation. RFB2A/B needs to
be low enough in value for the current through the resis-
tor chain to be at least 20μA in order to ignore the VOUTA/B
pin current.
To simplify the design, it is recommended to program the
desired output voltage from a standard 1.0V as shown in
Figure 2 with a proper C FF calculated from Equation 2. For
programming the output voltage from other standard
voltages, R FB1 , R FB2 and C FF need to be adjusted to conform
to the previous equations.
Maximum Power Dissipation
Each channel of SC286 has its own Θ JA of 32.5°C/W when
only one channel is in operation. Since both channels
are within the same package, there is about 50% of the
heat generated which will be transferred to the adjacent
channel. The equivalent total thermal impedance will be
higher when the neighboring channel is also in operation.
14
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