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参数资料
| 型号： | MAX1541ETL+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 28/49页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR DIVIDER PWM 40-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 620kHz |
| 占空比： | 100% |
| 电源电压： | 2 V ~ 28 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 是 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 40-WFQFN 裸露焊盘 |
| 包装： | 带卷 (TR) |
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Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
Inductor-Saturation Limit
The LSAT connection selects an upper current-sense
limit as the inductor-saturation threshold, or disables
the inductor-saturation protection feature altogether
(LSAT = GND). When enabled, the inductor-saturation
threshold is a multiple of the positive valley current-limit
threshold (Table 5) and tracks the valley current limit
when ILIM is adjusted. The selected inductor-saturation
threshold should give sufficient headroom above the
peak inductor current so switching noise does not acci-
dentally trip the saturation protection. Selecting an
excessively high threshold may allow inductor satura-
tion to go undetected. For an inductor with a low LIR
(the ratio of the inductor ripple current to the designed
maximum load current) near 20%, select the lowest sat-
uration threshold of 1.5 x I LIM(VAL) (LSAT = REF). When
using an inductor with a higher LIR, increase the induc-
tor-saturation threshold accordingly.
When inductor-saturation protection is enabled, the
MAX1540A/MAX1541 continuously monitor the inductor
current through the voltage across the current-sense
resistor. When the inductor-saturation threshold is
exceeded, the MAX1540A/MAX1541 immediately turn
off the high-side gate driver and enable a 6μA dis-
charge current on ILIM_ (Figure 7) at the beginning of
where the ILIM saturation fault sink current (I ILIM(LSAT) )
is typically 6μA (see the Electrical Characteristics
table). When using the default 50mV valley current-limit
threshold (ILIM_ = V CC ), the ILIM_ saturation fault sink
current does not lower the current-limit threshold
(Figure 5).
If the inductor current remains below the saturation
threshold during the next cycle, the controller disables
the ILIM_ discharge current, allowing the ILIM_ voltage
to return to its nominal set point. The inductor should
not remain in saturation once the controller reduces the
valley current limit. If the inductor remains saturated,
the output voltage may drop low enough to trip the
undervoltage fault protection (UVP enabled), causing
the MAX1540A/MAX1541 to set the fault latch and shut
down both outputs. Adding a capacitor from ILIM_ to
GND slows the ILIM_ voltage change by the time con-
stant τ = (R A || R B ) x C ILIM , where τ is between 5 to 10
switching periods. If the inductor saturation occurs only
during a short load transient, the time constant allows
the power supply to recover before the output voltage
drops below the output undervoltage threshold.
Set Δ V ILIM to be at least 30% of the ILIM_ set voltage.
Calculate R A and R B using the equations below:
Δ V ILIM = - ?
? R A R B ?
+R ?
? R A B ?
Δ V ILIM ?
Δ V ILIM ?
? ?
? with ?
? set at 30 %
?
R B =
? ?
- 1 ?
? V
the next DH_ on-time. This reduces the voltage on
ILIM_ by Δ V ILIM where:
I ILIM(LSAT)
R A =
V REF
I ILIM(LSAT) ? V ILIM(SET) ? ? V ILIM(SET) ?
R A
V REF
? ILIM(SET) ?
Inductor-saturation sensing works best when using a cur-
MAX1540A
MAX1541
REF
R A
C REF
rent-sense resistor in series with the inductor. See the
Setting the Current Limit section for various current-sense
configurations (Figure 14) and LSAT recommendations.
TO VALLEY
CURRENT-LIMIT
COMPARATOR
ILIM
C ILIM
Table 5. LSAT Configuration Table
(FIGURE 2)
FROM LSAT
COMPARATOR
AND LOGIC
(FIGURE 2)
6 μ A
R B
LSAT
V CC
Open
REF
GND
INDUCTOR-SATURATION THRESHOLD
2.00 x I LIM(VAL)
1.75 x I LIM(VAL)
1.50 x I LIM(VAL)
Disabled
Figure 7. Adjustable Current-Limit Threshold
28
______________________________________________________________________________________
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