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| 型号： | MAX1897ETP+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 20/33页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM 20-TQFN |
| 标准包装： | 2,500 |
| 系列： | Quick-PWM™ |
| PWM 型： | 控制器 |
| 输出数： | 1 |
| 频率 - 最大： | 550kHz |
| 电源电压： | 4.5 V ~ 5.5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 85°C |
| 封装/外壳： | 20-WQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
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Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
SLAVE
CONTROLLER
MASTER
CONTROLLER
ILIM
R C
C REF
REF
V ITHM ( HIGH ) =
1 ? R B ?
? ?
10 ? R A + R B ?
V REF
R D
MAX1887
MAX1897
R A
MAX1718
V ITHM ( HIGH ) =
1 ? R B // R LIMIT ?
? ?
10 ? R A + ( R B // R LIMIT ) ?
V REF
R LIMIT
LIMIT
C LIMIT
R B
ILIM
V ITHS =
1 ? R D ?
? ?
10 ? R C + R D ? V REF
Figure 5. Setting the Adjustable Current Limits
I LIMIT ( VALLEY ) ≥ ?
? ? ? ?
?
η
?
?
?
V OUT ( V IN ? V OUT )
≤ R B ≤
R A = ? ?
? ? 1 ? R B
current-limit threshold. This is acceptable since the
slave ’ s inductor current limit only serves as a fail-safe in
case the master and slave inductor currents become
significantly unbalanced during a transient.
The basic operating conditions are determined using
the same calculations provided in any Quick-PWM reg-
ulator data sheet. The valley of the inductor current
(I LIMIT(VALLEY) ) occurs at I LOAD(MAX) divided by the
number of phases minus half of the peak-to-peak
inductor current:
? I LOAD ( MAX ) ? ? ? I INDUCTOR ?
2
where the peak-to-peak inductor current may be deter-
mined by the following equation:
? I INDUCTOR =
V IN f SW L
The master ’ s high current-limit threshold must be set
high enough to support the maximum load current,
to support the maximum load current for the maximum
R DS(ON) and minimum current-limit tolerance value:
V ITHM(HIGH) ≥ (I LIMIT(VALLEY) )R DS(ON)(MAX)
where V ITHM , the master ’ s current-limit threshold, is typ-
ically 1/10th the voltage seen at the master ’ s ILIM input
(V ITHM = 0.1 x V LIM(MASTER) , see the master con-
troller ’ s data sheet). Connect a resistive voltage-divider
from the master controller ’ s internal reference to GND,
with the master ’ s ILIM input connected to the center tap
(Figure 5). Use 1% tolerance resistors in the divider with
10μA to 20μA DC bias current to prevent significant
errors due to the ILIM pin ’ s input current:
V ILIM ( MASTER ) V ILIM ( MASTER )
20 μ A 10 μ A
? ? V REF ( MASTER ) ? ?
? ?
? ? V ILIM ( MASTER ) ? ?
Configure the slave controller so its LIMIT output begins
to roll off after the master current-limit threshold occurs:
even when the master ’ s current-limit threshold is at its
minimum tolerance value, as described in the master
controller ’ s data sheet. Most Quick-PWM controllers
? V ITHM ( HIGH )
V ITHS ≥ R CM ?
? R DS ( ON )( MAX )
?
+ ? I INDUCTOR ?
?
that may be chosen as the master controller use the
low-side MOSFET ’ s on-resistance to sense the inductor
current. In these applications, the worst-case maximum
value for R DS(ON) plus some margin for the rise in
R DS(ON) over temperature must be used to determine
the master ’ s current-limit threshold. A good general rule
is to allow 0.5% additional resistance for each ° C of
temperature rise. Set the master current-limit threshold
where V ITHS , the slave ’ s current-limit threshold, is pre-
cisely one-tenth the voltage seen at the slave ’ s ILIM
input (V ITHS = 0.1 ? V ILIM(SLAVE) ). Connect a second
resistive voltage-divider from the master controller ’ s
internal reference to GND, with the slave ’ s ILIM input
connected to the center tap (Figure 5). The external
adjustment range of 400mV to 1.5V corresponds to a
20
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