参数资料
型号: MAX17080GTL+
厂商: Maxim Integrated Products
文件页数: 40/48页
文件大小: 0K
描述: IC CONTROLLER AMD SVI 40-TQFN
标准包装: 60
应用: 控制器,AMD SVI
输入电压: 2.7 V ~ 5.5 V
输出数: 3
输出电压: 0.013 V ~ 1.55 V
工作温度: -40°C ~ 105°C
安装类型: 表面贴装
封装/外壳: 40-WFQFN 裸露焊盘
供应商设备封装: 40-TQFN-EP(5x5)
包装: 管件
AMD 2-/3-Output Mobile Serial
VID Controller
? ? V ? ? ? I ? 2
PD (N L Resistive) = ? 1 ? ?? ? ? ? LOAD ? R DS ( ON )
?
Ideally, the losses at V IN(MIN) should be roughly equal to
losses at V IN(MAX) , with lower losses in between. If the
losses at V IN(MIN) are significantly higher than the losses
at V IN(MAX) , consider increasing the size of N H (reducing
R DS(ON) but with higher C GATE ). Conversely, if the loss-
es at V IN(MAX) are significantly higher than the losses at
V IN(MIN) , consider reducing the size of N H (increasing
R DS(ON) to lower C GATE ). If V IN does not vary over a
wide range, the minimum power dissipation occurs
where the resistive losses equal the switching losses.
Choose a low-side MOSFET that has the lowest possible
on-resistance (R DS(ON) ), comes in a moderate-sized
package (i.e., one or two 8-pin SOs, DPAK, or D 2 PAK),
and is reasonably priced. Make sure that the DL gate dri-
ver can supply sufficient current to support the gate
charge and the current injected into the parasitic gate-to-
drain capacitor caused by the high-side MOSFET turning
on; otherwise, cross-conduction problems might occur
(see the Core SMPS MOSFET Gate Drivers section).
Switching losses in the high-side MOSFET can become
an insidious heat problem when maximum AC adapter
voltages are applied, due to the squared term in the C
x V IN 2 x f SW switching-loss equation. If the high-side
MOSFET chosen for adequate R DS(ON) at low battery
voltages becomes extraordinarily hot when biased from
V IN(MAX) , consider choosing another MOSFET with
lower parasitic capacitance.
For the low-side MOSFET (N L ), the worst-case power
dissipation always occurs at maximum input voltage:
OUT
? ?
? ? V IN ( MAX ) ? ? ? η TOTAL ?
The worst case for MOSFET power dissipation occurs
under heavy overloads that are greater than
I LOAD(MAX) , but are not quite high enough to exceed
the current limit and cause the fault latch to trip. To pro-
tect against this possibility, the circuit can be “overde-
= I PEAK ( MAX ) ? ??
??
?
?
Core MOSFET Power Dissipation
Worst-case conduction losses occur at the duty factor
extremes. For the high-side MOSFET (N H ), the worst-
signed” to tolerate:
I LOAD ( MAX ) = I PEAK ( MAX ) ?
? I INDUCTOR
2
? I LOAD ( MAX ) LIR ?
2
PD (N H Resistive) = ? OUT ? I LOAD DS ( O N )
(
) 2 ? ? C I RSS f SW ? ? I LOAD
? ?
PD (N H Switching) = V IN ( MAX )
N × Q GATE
case power dissipation due to resistance occurs at the
minimum input voltage:
? V ? 2
R
? V IN ?
where I LOAD is the per-phase current.
Generally, a small high-side MOSFET is desired to
reduce switching losses at high input voltages.
However, the R DS(ON) required to stay within package
power dissipation often limits how small the MOSFET
can be. Again, the optimum occurs when the switching
losses equal the conduction (R DS(ON) ) losses. High-
side switching losses do not usually become an issue
until the input is greater than approximately 15V.
Calculating the power dissipation in the high-side
MOSFET (N H ) due to switching losses is difficult since it
must allow for difficult quantifying factors that influence
the turn-on and turn-off times. These factors include the
internal gate resistance, gate charge, threshold voltage,
source inductance, and PCB layout characteristics. The
following switching-loss calculation provides only a very
rough estimate and is no substitute for breadboard
evaluation, preferably including verification using a
thermocouple mounted on N H :
:
GAT E
where C RSS is the reverse transfer capacitance of N H ,
I GATE is the peak gate-drive source/sink current (1A,
typ), and I LOAD is the per-phase current.
where I PEAK(MAX) is the maximum valley current
allowed by the current-limit circuit, including threshold
tolerance and on-resistance variation. The MOSFETs
must have a good-sized heatsink to handle the over-
load power dissipation.
Choose a Schottky diode (D L ) with a forward voltage
low enough to prevent the low-side MOSFET body
diode from turning on during the dead time. As a gen-
eral rule, select a diode with a DC current rating equal
to 1/3 the load current per phase. This diode is optional
and can be removed if efficiency is not critical.
Core Boost Capacitors
The boost capacitors (C BST ) must be selected large
enough to handle the gate-charging requirements of
the high-side MOSFETs. Typically, 0.1μF ceramic
capacitors work well for low-power applications driving
medium-sized MOSFETs. However, high-current appli-
cations driving large, high-side MOSFETs require boost
capacitors larger than 0.1μF. For these applications,
select the boost capacitors to avoid discharging the
capacitor more than 200mV while charging the high-
side MOSFETs’ gates:
C BST =
200 mV
where N is the number of high-side MOSFETs used for
one SMPS, and Q GATE is the gate charge specified in the
MOSFET ’s data sheet. For example, assume two
IRF7811W n-channel MOSFETs are used on the high
40
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