MAX1531ETJ+ Maxim Integrated Products, MAX1531ETJ+ Datasheet - Page 25

• Manufacturer Part Number: MAX1531ETJ+
• Description: IC PS CTRLR MULTI-OUTPUT 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1531ETJ+

• Applications: Five Power Supply Monitor
• Voltage - Supply: 4.5 V ~ 28 V
• Current - Supply: 1.7mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Voltage - Output: 1.25 ~ 16.5 V
• Number Of Outputs: 5
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Input: -
• Lead Free Status / Rohs Status: Details

amplifier g
regulation V
Use the following to calculate the slope compensation
change during the sag:
where D
which is usually 50%.
The actual undershoot is always equal to or bigger than
the worst of V
The amplitude of the soar due to the finite output
capacitance and inductor slew rate is a function of the
load step, the output capacitor value, the inductor
value, and the output voltage:
The amplitude of the overshoot due to the AC load reg-
ulation is:
where ΔSC
tion during the overshoot, given by:
where D
shoot, which is typically 0%.
Similarly, the actual overshoot is always equal to or big-
ger than the worst of V
V
Given the component values in the circuit of Figure 1,
during a 1.5A step load transient, the voltage step due to
capacitor ESR is negligible. The voltage sag due to finite
capacitance and inductor slew rate is 81mV, and the
voltage undershoot due to the AC load regulation is
170mV. The total undershoot seen in the Typical
OVER_AC
V
V
UNDER AC
OVER AC
ΔSC
ΔSC
Multiple-Output Power-Supply Controllers for
UNDER
OVER
UNDER
_
.
m
_
OVER
OVER
FB
, the compensation resistor R
V
ESR_STEP
=
, and the output voltage set point V
SOAR LC
is the duty cycle at the peak of the over-
=
is the duty cycle at the valley of the sag,
V
=
is the change of the slope compensa-
V
OUT
=
OUT
______________________________________________________________________________________
437 5
_
437 5
×
.
, V
×
.
=
mV
⎛
⎜
⎝
V
SAG_LC
mV
2
A
+
⎛
⎜
⎝
FB
V
ESR_STEP
A
+
Δ
FB
L
×
VCS
Δ
×
SC
VCS
C
×
×
×
SC
×
(
R
OUT
⎛
⎜
⎝
Δ
OVER
R
×
D
COMP
⎛
⎜
⎝
I
UNDER
, and V
×
LOAD
COMP
R
UNDER
V
R
V
DS ON
OUT
×
IN
DS ON
V
, V
(
OUT
×
(
)
2
-
×
UNDER_AC
g
SOAR_LC
)
g
m
-
D
COMP
)
×
m
OVER
×
V
Δ
V
Δ
OUT
I
LOAD
IN
I
LOAD
, the FB
⎞
⎟
⎠
OUT
⎞
⎟
⎠
, and
.
⎞
⎟
⎠
⎞
⎟
⎠
:
Operating Characteristics is 170mV. The voltage soar
due to finite capacitance and inductor slew rate is
155mV, and the voltage overshoot due to the AC load
regulation is 167mV. The total overshoot seen the in the
Typical Operating Characteristics is 200mV.
The step-down controller of the MAX1530/MAX1531
uses a peak current-mode control scheme that regu-
lates the output voltage by forcing the required current
through the inductor. The MAX1530/MAX1531 use the
voltage across the high-side MOSFET’s R
sense the inductor current. Using the current-sense
amplifier’s output signal and the amplified feedback
voltage sensed at FB, the control loop sets the peak
inductor current by:
where V
is the gain of the current-sense amplifier (3.5 typical),
A
V
is the on-resistance of the high-side MOSFET.
The total DC loop gain (A
R
In the above equation, D’ = 1 - D, n is a factor deter-
mined by the slope compensation m
current ramp m
The slope compensation of the MAX1530/MAX1531 is
219mV/µs. The inductor current ramp is a function of
the input voltage, output voltage, inductance, high-side
MOSFET on-resistance R
current-sense amplifier A
OUT(SET)
VEA
LE
is the equivalent load resistance, given by:
is the DC gain of the error amplifier (2000 typ),
I
PEAK
FB
m
A
R
is the output voltage set point, and R
1
= 1.238V is the FB regulation voltage, A
DC
LE
=
=
=
(
=
1
V
V
, as shown below:
OUT
V
V
⎛
⎜
⎝
IN
OUT SET
OUT SET
I
LOAD MAX
-
V
L
V
V
-
FB
n
OUT
(
(
OUT
V
LCD Monitors
OUT SET
(
=
VCS
DC
×
)
)
1
DS(ON)
×
×
R
×
(
) is approximately:
+
)
, and is:
LE
R
R
R
⎞
⎟
⎠
m
m
DS ON
DS ON
DS ON
||
C
Compensation Design
)
1
×
)
(
⎛
⎜
⎝
(
, and the gain of the
(
×
n
L
A
V
×
)
)
FB
VEA
×
)
c
×
×
×
D D
and the inductor
A
A
×
f
A
SW
'
-
VCS
VCS
A
VCS
VEA
⎞
⎟
⎠
DS(ON)
DS(ON)
VCS
25
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