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ADP1874ARQZ-0.3-R7 датащи(PDF) 33 Page - Analog Devices

номер детали ADP1874ARQZ-0.3-R7
подробное описание детали  Synchronous Buck Controller with Constant On-Time and Valley Current Mode
PDF  44 Pages
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производитель  AD [Analog Devices]
домашняя страница  http://www.analog.com
Logo AD - Analog Devices

ADP1874ARQZ-0.3-R7 датащи(HTML) 33 Page - Analog Devices

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ADP1874/ADP1875
Rev. 0 | Page 33 of 44
Assuming an overshoot of 45 mV, determine if the output
capacitor that was calculated previously is adequate.
ZERO
COMP
COMP
f
R
C
π
=
2
1
()
()
2
2
2
6
2
2
2
)
8
.
1
(
)
mV
45
8
.
1
(
)
A
15
(
10
1
)
(
)
(
−
−
×
×
=
−
Δ
−
×
=
−
OUT
OVSHT
OUT
LOAD
OUT
V
V
V
I
L
C
= 1.4 mF
=
3
3
10
25
.
6
10
25
.
60
14
.
3
2
1
×
×
×
×
×
= 423 pF
Loss Calculations
Duty cycle = 1.8/12 V = 0.15
Choose five 270 μF polymer capacitors.
RON (N2) = 5.4 mΩ
The rms current through the output capacitor is
tBODY(LOSS) = 20 ns (body conduction time)
A
49
.
1
V
2
.
13
V
8
.
1
10
300
μF
1
)
V
8
.
1
V
2
.
13
(
3
1
2
1
)
(
3
1
2
1
3
,
,
=
×
×
×
−
×
=
×
×
−
×
=
MAX
IN
OUT
SW
OUT
MAX
IN
RMS
V
V
f
L
V
V
I
VF = 0.84 V (MOSFET forward voltage)
CIN = 3.3 nF (MOSFET gate input capacitance)
QN1,N2 = 17 nC (total MOSFET gate charge)
RGATE = 1.5 Ω (MOSFET gate input resistance)
()
[
] 2
1
LOAD
N2(ON)
N1(ON)
N1,N2(CL)
I
R
D
R
D
P
×
×
−
+
×
=
= (0.15 × 0.0054 + 0.85 × 0.0054) × (15 A)2
= 1.215 W
The power loss dissipated through the ESR of the output
capacitor is
PCOUT = (IRMS)2 × ESR = (1.5 A)2 × 1.4 mΩ = 3.15 mW
Feedback Resistor Network Setup
2
)
(
)
(
×
×
×
=
F
LOAD
SW
LOSS
BODY
LOSS
BODY
V
I
t
t
P
= 20 ns × 300 × 103 × 15 A × 0.84 × 2
= 151.2 mW
Choosing RB = 1 kΩ as an example, calculate RT as follows:
kΩ
2
V
6
.
0
V)
6
.
0
V
8
.
1
(
kΩ
1
=
−
×
=
T
R
PSW(LOSS) = fSW × RGATE × CTOTAL × ILOAD × VIN × 2
= 300 × 103 × 1.5 Ω × 3.3 × 10−9 × 15 A × 12 × 2
= 534.6 mW
Compensation Network
To calculate RCOMP, CCOMP, and CPAR, the transconductance
parameter and the current-sense gain variable are required. The
transconductance parameter (Gm) is 500 μA/V, and the current-
sense loop gain is
(
)
[
]
()
[]
))
002
.
0
0
.
5
10
3
.
3
10
300
(
0
.
5
(
))
002
.
0
62
.
4
10
3
.
3
10
300
(
62
.
4
(
9
3
9
3
)
(
+
×
×
×
×
×
+
+
×
×
×
×
×
=
+
×
+
+
×
=
−
−
BIAS
lowerFET
SW
BIAS
DR
upperFET
SW
DR
LOSS
DR
I
VREG
C
f
VREG
I
V
C
f
V
P
A/V
33
.
8
005
.
0
24
1
1
=
×
=
×
=
ON
CS
CS
R
A
G
where ACS and RON are taken from setting up the current limit
(see the Programming Resistor (RES) Detect Circuit section
and the Valley Current-Limit Setting section).
= 57.12 mW
mW
6
.
55
)
002
.
0
5
10
3
.
3
10
300
(
)
V
5
V
13
(
)
(
)
(
9
3
)
(
=
+
×
×
×
×
×
−
=
+
×
×
×
−
=
−
BIAS
total
SW
IN
LDO
DISS
I
VREG
C
f
VREG
V
P
The crossover frequency is 1/12 the switching frequency.
300 kHz/12 = 25 kHz
PCOUT = (IRMS)2 × ESR = (1.5 A)2 × 1.4 mΩ = 3.15 mW
The zero frequency is 1/4 the crossover frequency.
2
)
(
LOAD
LOSS
DCR
I
DCR
P
×
=
= 0.003 × (15 A)2 = 675 mW
25 kHz/4 = 6.25 kHz
()
()
CS
M
REF
OUT
L
OUT
OUT
L
ZERO
CROSS
CROSS
COMP
G
G
V
V
R
C
ESR
s
C
ESR
R
s
f
f
f
R
1
1
1
)
(
1
2
2
2
2
2
2
×
×
×
×
×
+
+
+
×
+
=
PCIN = (IRMS)2 × ESR = (7.5 A)2 × 1 mΩ = 56.25 mW
()
()
8
.
1
15
3
.
8
10
500
1
6
.
0
8
.
1
0011
.
0
0035
.
0
25
2
1
0011
.
0
)
0035
.
0
)
15
8
.
1
((
25
2
1
25
.
6
25
25
6
2
2
2
2
2
2
×
×
×
×
×
×
×
×
π
+
×
+
×
×
π
+
×
+
=
−
k
k
k
k
K
R
COMP
= 60.25 kΩ
PLOSS = PN1,N2 + PBODY(LOSS) + PSW + PDCR + PDR + PDISS(LDO) +
PCOUT + PCIN
= 1.215 W + 151.2 mW + 534.6 mW + 57.12 mW + 55.6 +
3.15 mW + 675 mW + 56.25 mW
= 2.655 W



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