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| 型号： | ADP1877HC-EVALZ |
| 厂商： | Analog Devices Inc |
| 文件页数： | 22/32页 |
| 文件大小： | 0K |
| 描述： | BOARD EVALUATION 13A ADP1877 |
| 标准包装： | 1 |
| 主要目的： | DC/DC，步降 |
| 输出及类型： | 2，非隔离 |
| 输出电压： | 1.05V，1.8V |
| 电流 - 输出： | 13A |
| 输入电压： | 6 ~ 14 V |
| 稳压器拓扑结构： | 降压 |
| 频率 - 开关： | 600kHz |
| 板类型： | 完全填充 |
| 已供物品： | 板 |
| 已用 IC / 零件： | ADP1877 |
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ADP1877
Then the power loss in the low-side MOSFET is
P LS = P CLS + P BODYDIODE
Data Sheet
Because the zero produced by the ESR of the output capacitor is
not needed to stabilize the control loop, the ESR is ignored for
analysis. Then Z FILTER is given by
Note that MOSFET, R DSON , increases with increasing
temperature with a typical temperature coefficient of 0.4%/ o C.
The MOSFET junction temperature rise over the ambient
Z FILTER =
1
sC OUT
(3)
temperature is
Because C C2 is very small relative to C COMP , Z COMP can be written as
T J = T A + θ JA × P D
where:
Z COMP = R COMP +
1
sC COMP
=
1 + sR COMP × C COMP
sC COMP
(4)
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.
At the crossover frequency, the open loop transfer function is
unity of 0 dB, H (f CROSS ) = 1. Combining Equation 1 and
LOOP COMPENSATION
As with most current mode step-down controller, a transcon-
ductance error amplifier is used to stabilize the external voltage
Z COMP ( f CROSS ) = (
2 π × f CROSS
G m × G CS
)(
C OUT × V OUT
V REF
)
(5)
loop. Compensating the ADP1877 is fairly easy; an RC
The zero produced by R COMP and C COMP is
shows the configuration of the compensation components:
R COMP , C COMP , and CC2. Because C C2 is very small compared to
f ZERO =
1
2 π R COMP × C COMP
(6)
C COMP , to simplify calculation, C C2 is ignored for the stability
At the crossover frequency, Equation 4 can be shown as
compensation analysis.
COMPx
Z COMP ( f CROSS ) = R COMP ×
f CROSS + f ZERO
f CROSS
(7)
f CROSS 2 π × f CROSS C × V OUT
f CROSS + f ZERO
G m × G CS
C C2
R COMP
C COMP
G m
0.6V
FBx
Combining Equation 5 and Equation 7 and solving for R COMP
gives
R COMP = × ( ) × ( OUT )
V REF
(8)
AGND
Choose the crossover and zero frequencies as follows:
= SW
ADP1877
Figure 34. Compensation Components
The open loop gain transfer function at angular frequency, s, is
given by
f CROSS =
f ZERO =
f SW
13
f CROSS f
5 65
(9)
(10)
H ( s ) = G m × G CS ×
V REF
V OUT
× Z COMP ( s ) × Z FILTER ( s )
(1)
Substituting Equation 2, Equation 9, and Equation 10 into
Equation 8 yields
2 π × f CROSS C OUT × V OUT
where:
G m is the transconductance of the error amplifer, 500 μs.
G CS is the tranconductance of the current sense amplifier.
Z COMP is the impedance of the compensation network.
Z F ILTER is the impedance of the output filter.
V REF = 0.6 V
G CS with units of A/V is given by
R COMP = 0 . 83 × A CS × R DSON ( ) × ( ) (11)
G m V REF
where:
G m is the transconductance of the error amplifer, 500 μs.
A CS is the current sense gain of 3 V/V, 6 V/V, 12 V/V or 24 V/V.
R DSON is on resistance of the low-side MOSFET.
V REF = 0.6 V
G CS =
A CS × R DSON _ MIN
C COMP =
1
(2)
where:
A CS is the current sense gain of either 3 V/V, 6 V/V, 12 V/V, or
24 V/V set by the gain resistor between DL and PGND.
And combining Equation 6 and Equation 10 yields
2
π R COMP × f CROSS
And lastly set C C2 to
(12)
× C COMP ≤ C C 2 ≤ × C COMP
R DSON_MIN is the the low-side MOSFET minimum on resistance.
1
20
1
10
(13)
Rev. D | Page 22 of 32
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