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参数资料
| 型号： | ADP1850DP-EVALZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 17/32页 |
| 文件大小： | 0K |
| 描述： | EVAL BOARD FOR ADP1850DP |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 1.09V |
| 电流 - 输出： | 50A |
| 输入电压： | 10 ~ 15 V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 300kHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | ADP1850DP |
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Data Sheet
ADP1850
ACCURATE CURRENT - LIMIT SENSING
R DSON of the MOSFET can vary by more than 50% over the
temperature range. Accurate current limit sensing is achieved
by adding a current sense resistor from the source of the low-
RAMP
ADP1850
R RAMP
V IN
side MOSFET to PGNDx. Make sure that the power rating of the
current sense resistor is adequate for the application. Apply the
previous equation and calculate R ILIM by replacing R DSON_MAX
with R SENSE . Figure 30 illustrates the implementation of accurate
current limit sensing.
DHx
SWx
ILIMx
DLx
R ILIM
R CSG
ADP1850
DHx
V IN
Figure 31. Slope Compensation and CS Gain Connection
SETTING THE CURRENT SENSE GAIN
SWx
ILIMx
R ILIM
The voltage drop across the external low-side MOSFET is
sensed by a current sense amplifier by multiplying the peak
R RAMP =
DLx
R SENSE
Figure 30. Accurate Current Limit Sensing
SETTING THE SLOPE COMPENSATION
In a current-mode control topology, slope compensation is
needed to prevent subharmonic oscillations in the inductor
current and to maintain a stable output. The external slope
compensation is implemented by summing the amplified sense
signal and a scaled voltage at the RAMPx pin. To implement the
slope compensation, connect a resistor between RAMPx and
the input voltage. The resistor, R RAMP , is calculated by
7 × 10 9 L
A CS × R DSON _ MAX
where:
inductor current and the R DSON of the MOSFET. The result is
then amplified by a gain factor of either 3 V/V, 6 V/V, 12 V/V,
or 24 V/V, which is programmable by an external resistor, R CSG ,
connected to the DLx pin. This gain is sensed only during
power-up and not during normal operation. The amplified
voltage is summed with the slope compensation ramp voltage
and fed into the PWM controller for a stable regulation voltage.
The voltage range of the internal node, V CS , is between 0.4 V
and 2.2 V. Select the current sense gain such that the internal
minimum amplified voltage (V CSMIN ) is above 0.4 V and the
maximum amplified voltage (V CSMAX ) is 2.1 V. Note that V CSMIN
or V CSMAX is not the same as V COMP , which has a range of 0.85 V
to 2.25 V. Make sure that the maximum V COMP (V COMPMAX ) does
not exceed 2.2 V to account for temperature and part-to-part
variations. See the following equations for V CSMIN , V CSMAX , and
V COMPMAX :
7 × 10 9 is an internal parameter.
L is the inductance (with units in H) of the inductor.
V CSMIN = 0 . 75 V ?
1
2
I LPP × R DSON _ MIN × A CS
R DSON_MAX is the low-side MOSFET maximum on resistance.
A CS is the gain, either 3 V/V, 6 V/V, 12 V/V, or 24 V/V, of the
V CSMAX = 0 . 75 V + ( I LOADMAX ?
1
2
I LPP ) × R DSON _ MAX × A CS
section for more details).
R DSON is temperature dependent and can vary as much as
V COMPMAX =
( V IN ? 0 . 2 V ) t ON
100 pF × R RAMP
+ V CSMAX
0.4%/ o C. Choose R DSON at the maximum operating temperature.
The voltage at RAMPx is fixed at 0.2 V, and the current going
into RAMPx should be between 10 μA and 160 μA. Make sure
that the following condition is satisfied:
where:
V CSMIN is the minimum amplified voltage of the internal current
sense amplifier at zero output current.
V CSMAX is the maximum amplified voltage of the internal current
10 μ A ≤
V IN ? 0 . 2 V
R RAMP
≤ 160 μ A
sense amplifier at maximum output current.
R DSON_MIN is the low-side MOSFET minimum on resistance. The
zero-current level voltage of the current sense amplifier is 0.75 V.
For instance, with an input voltage of 12 V, R RAMP should not
exceed 1.1 MΩ. If the calculated R RAMP produces less than 10 μA,
then select an R RAMP value that produces between 10 μA and 15 μA.
resistor, R RAMP , and the current sense gain resistor, R CSG .
I LPP is the peak-to-peak ripple current in the inductor.
I LOADMAX is the maximum output dc load current.
V COMPMAX is the maximum voltage at the COMP pin.
100 pF is an internal parameter.
t ON is the high-side driver (DH) on time.
Rev. A | Page 17 of 32
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