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| 型号： | ADP1850DP-EVALZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 20/32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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ADP1850
The high-side MOSFET transition loss is approximated by the
equation
Data Sheet
The total power dissipation of the high-side MOSFET is the
sum of conduction and transition losses:
P T ?
V IN × I LOAD × ( t R + t F ) × f SW
2
P HS ? P C + P T
The synchronous rectifier, or low-side MOSFET, carries the
t R ?
where:
P T is the high-side MOSFET switching loss power.
t R is the rise time in charging the high-side MOSFET.
t F is the fall time in discharging the high-side MOSFET.
t R and t F can be estimated by
Q GSW
I DRIVER _ RISE
inductor current when the high-side MOSFET is off. The low-
side MOSFET transition loss is small and can be neglected in
the calculation. For high input voltage and low output voltage,
the low-side MOSFET carries the current most of the time.
Therefore, to achieve high efficiency, it is critical to optimize
the low-side MOSFET for low on resistance. In cases where the
power loss exceeds the MOSFET rating or lower resistance is
required than is available in a single MOSFET, connect multiple
t F ?
Q GSW
I DRIVER _ FALL
low-side MOSFETs in parallel. The equation for low-side
MOSFET conduction power loss is
where:
Q GSW is the gate charge of the MOSFET during switching and is
given in the MOSFET data sheet.
I DRIVER_RISE and I DRIVER_FALL are the driver current put out by the
ADP1850 internal gate drivers.
If Q GSW is not given in the data sheet, it can be approximated by
? V ?
P CLS ? ( I LOAD ) 2 × R DSON ? 1 ? OUT ?
? V IN ?
There is also additional power loss during the time, known as
dead time, between the turn-off of the high-side switch and the
turn-on of the low-side switch, when the body diode of the low-
side MOSFET conducts the output current. The power loss in
Q GSW ? Q GD +
Q GS
2
the body diode is given by
P BODYDIODE = V F × t D × f SW × I O
where:
Q GD and Q GS are the gate-to-drain and gate-to-source charges
given in the MOSFET data sheet.
I DRIVER_RISE and I DRIVER_FALL can be estimated by
where:
V F is the forward voltage drop of the body diode, typically 0.7 V.
t D is the dead time in the ADP1850 , typically 30 ns when driving
some medium-size MOSFETs with input capacitance, C iss , of
I DRIVER _ RISE ?
I DRIVER _ FALL ?
where:
V DD ? V SP
R ON _ SOURCE + R GATE
V SP
R ON _ SINK + R GATE
approximately 3 nF. The dead time is not fixed. Its effective
value varies with gate drive resistance and C iss , so P BODYDIODE
increases in high load current designs and low voltage designs.
Then the power loss in the low-side MOSFET is
P LS = P CLS + P BODYDIODE
V DD is the input supply voltage to the driver and is between 2.75 V
and 5 V, depending on the input voltage.
V SP is the switching point where the MOSFET fully conducts;
this voltage can be estimated by inspecting the gate charge
graph given in the MOSFET data sheet.
R ON_SOURCE is the on resistance of the ADP1850 internal driver,
given in Table 1 when charging the MOSFET.
R ON_SINK is the on resistance of the ADP1850 internal driver,
given in Table 1 when discharging the MOSFET.
R GATE is the on gate resistance of MOSFET given in the
Note that MOSFET, R DSON , increases with increasing tempera-
ture with a typical temperature coefficient of 0.4%/ o C. The
MOSFET junction temperature (T J ) rise over the ambient
temperature is
T J = T A + θ JA × P D
where:
θ JA is the thermal resistance of the MOSFET package.
T A is the ambient temperature.
P D is the total power dissipated in the MOSFET.
MOSFET data sheet. If an external gate resistor is added, add
this external resistance to R GATE .
Rev. A | Page 20 of 32
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