参数资料
| 型号： | MIC2150YML TR |
| 厂商： | Micrel Inc |
| 文件页数： | 13/27页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM 24MLF |
| 标准包装： | 1 |
| PWM 型： | 电流/电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 550kHz |
| 占空比： | 80% |
| 电源电压： | 4.5 V ~ 14.5 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： | -40°C ~ 125°C |
| 封装/外壳： | 24-VFQFN 裸露焊盘，24-MLF? |
| 包装： | 标准包装 |
| 其它名称： | 576-3746-6 |
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V OUT × T DLY
I SET = I PK ?
I SET × R DSON ( MAX )
V OUT 3 . 3 V
I RIPPLE =
= 9 . 11 A
I PK = 5 + = 9 . 55 A
I SET = 9 . 55 A ?
= 8 . 89 A
R CS =
= 494 Ω
Micrel, Inc.
L
Rcs can now be calculated using:
R CS =
I CS min
Where:
D = Duty Cycle
F S = Switching Frequency
L = Power inductor value
T DLY = Current limit blanking time ~ 100ns
I CS(min) = 180μA
Example
Consider a 12V to 3.3V @ 5A converter with 0.5μH
power inductor and 90% efficiency at full load.
D ≈ = = 31 %
V IN × Efficiency 12 V × 0 . 9
3 . 3 V × (1 ? 0 . 31)
500 kHz × 0 . 5 μH
9 . 11
2
3 . 3 v × 100ns
0 . 5 μH
8 . 89 × 10m Ω
180 μA
Using the simple method here would result in a current
limit point much lower than expected.
This equation sets the minimum current limit point of the
converter, but maximum will depend on the actual
inductor value and R DSON of the MOSFET under current
limit conditions. This could be in the region of 50%
higher and should be considered to ensure that all the
power components are within their thermal limits unless
thermal protection is implemented separately.
It is recommended to connect a 22pF capacitor from CS
to AGND close to the pins of the IC to prevent adjacent
channel switching noise from affecting the current limit
behavior.
Over Voltage Protection
If the voltage at the FB pin is detected to be 15% higher
than nominal for >2μs, the channel is stopped from
switching immediately and latched off. Switching can be
re-started by taking EN below the channel’s enable
threshold and re-enabling or re-cycling power to the IC.
Power Good Output
The power good output (PG) will go high only when both
Channel outputs are above 90% of their nominal set
output voltage. If CH2 is disabled (EN<2V), then PG will
MIC2150
be low regardless of the state of CH1. If PG functionality
is required for CH1 only, FB2 can be driven externally
above 90% V REF to enable PG to operate on CH1 only.
Enable
Sometimes, at high currents, it is possible to see
relatively large ground current peaks. These, in turn, can
create voltage differentials between AGND points. In
order to prevent these from affecting the converter
operation, it is good practice to drive enable 0.5V higher
than its maximum threshold i.e., >2.8V for both
channels.
V DD Regulator
The internal regulator provides a regulated 5V for
supplying the analogue circuit power (AV DD ) and the
MOSFET driver power from the input supply (V IN ). While
this is designed to operate in dropout at input voltages
down to 3V, driver current will be limited while the V DD
regulator is in dropout. It is therefore recommended that
for V IN ranges 5V to 7V, MOSFET gate current should be
kept to less than 50mA.
The AV DD supply should be connected to V DD through an
RC filter to provide decoupling of the switching noise
generated by the MOSFET drivers taking large current
steps from the V DD regulator.
Gate Drivers
The MIC2150 is designed to drive both high-side and
low-side N-Channel MOSFETs to enable high switching
speeds and the lowest possible losses. The high-side
MOSFET driver is supplied by bootstrapping the
switching voltage at the Drain of the lower MOSFET to
V DD . This provides the high-side MOSFET with a
constant VGS drive voltage equal to V DD .
Figure 7. High-Side Gate Drive Circuit and Waveform
When HSD goes high, this turns on the high-side
MOSFET and the SW node rises sharply. This is
coupled through the bootstrap capacitor C BST and Diode
D BST becomes reverse biased. The MOSFET Gate is
held at V DD - 0.5V above the Source for as long as C BST
remains charged. The bias current of the high-side driver
is <10mA so 100nF is sufficient to hold the gate voltage
with minimal droop for the power stroke (High-side
August 2009
13
M9999-082809-A
(408) 944-0800
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| MIC2151 | 制造商:MICREL 制造商全称:Micrel Semiconductor 功能描述:2-Phase Dual Output PWM Synchronous Buck Control IC |
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