isl88550a Intersil Corporation, isl88550a Datasheet - Page 22

• Manufacturer Part Number: isl88550a
• Description: Synchronous Step Down Controller With Sourcing And Sinking Ldo Regulator
• Manufacturer: Intersil Corporation

Transient Response (Buck)
The inductor ripple current also affects transient response
performance, especially at low V
inductor values allow the inductor current to slew faster,
replenishing charge removed from the output filter capacitors
by a sudden load step. The output sag is also a function of
the maximum duty factor, which can be calculated from the
on-time and minimum off-time as shown in Equation 33:
V
SAG
100k Ω
=
2
R3
R3
R3
C
L
OUT
×
2x10µF
Δ
×
I
VTT: 0.9V±1.5A
LOAD
AVDD
AVDD
AVDD
AVDD
V
C4
C4
OUT
1.5V
1.5V
1.5V
1.5V
(
MAX
⎡
⎢
⎣
100k Ω
R2
10µF
(
V
)
2
C2
C2
C2
C2
IN
1µF
C3
C3
⎡
⎢
⎣
C9: OPEN
V
−
OUT
V
V
V
OUT
IN
IN
×
K
)
×
22
+
K
t
OFF
+
IN
t
OFF
(
MIN
AVDD
SS
TON
SKIP#
GND
STBY#
SHDNA#
POK2
POK1
VTTI
VTT
VTTS
PGND2
AVDD
SS
TON
SKIP#
GND
STBY#
SHDNA#
POK2
POK1
VTTI
VTT
VTTS
PGND2
- V
(
MIN
)
⎤
⎥
⎦
OUT
)
⎤
⎥
⎦
FIGURE 29. TYPICAL DDR II APPLICATIONS CIRCUIT
ISL88550A
differentials. Low
ISL88550A
OVP/UVP
UGATE
PGND1
PHASE
LGATE
OVP/UVP
REFIN
BOOT
VTTR
UGATE
PHASE
PGND1
LGATE
(EQ. 33)
VDD
OUT
REFIN
BOOT
REF
ILIM
VTTR
VIN
VDD
OUT
ILIM
REF
VIN
FB
FB
ISL88550A
200k Ω
0.9V/10mA
0.9V/10mA
R4
C7
C7
C7
C7
0.22µF
where t
Specifications” on page 3) and K is from Table 1.
The overshoot during a full-load to no-load transient due to
stored inductor energy can be calculated using Equation 34:
C6
C6
C10
C10
C10
C10
0.22µF
1µF
V
SOAR
Q1
Q1
Q1
Q1
=
OFF(MIN)
2
Δ
×
I
Q2
Q2
LOAD
C5: 4.7µF
C
R5
OUT
R1: 182k Ω
C8: 2x10µF
56.2k Ω
1.0µH, 35A, 2m Ω
1.0uH, 35A, 2m
5V BIAS SUPPLY
FALCO ER1309
FALCO ER1309
(
MAX
×
C1
C1
OPEN
V
)
2
is the minimum off-time (see the “Electrical
OUT
×
L1:
L
VIN: 4.5V TO 25V
-
Q1: IRF7821/30V/9m Ω
Q2: IRF7832/30V/5m Ω
C11
C11
C11
C11
150
220
220µF
12m Ω
12m
12m
12m
15.8k Ω
R6
R1
10k Ω
C14
C14
470µF
(OPTIONAL)
1.8V/12A
1.8V/12A
VDDQ
VDDQ
C12
C12
C12
C12
150ÿF
220ÿF
150ÿF
220µF
12m Ω
12m
12m
12m
October 1, 2007
C13
C13
C13
C13
1µF
(EQ. 34)
FN6168.2