MAX17020ETJ+T Maxim Integrated Products, MAX17020ETJ+T Datasheet - Page 29

• Manufacturer Part Number: MAX17020ETJ+T
• Description: IC CTLR PWM DUAL STEP DN 32-TQFN
• Manufacturer: Maxim Integrated Products
• Series: Quick-PWM™r

Specifications of MAX17020ETJ+T

• Applications: Power Supplies
• Current - Supply: 1mA
• Voltage - Supply: 6 V ~ 24 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Also, keep in mind that transient response performance
of buck regulators operated too close to dropout is poor,
and bulk output capacitance must often be added (see
the V
The absolute point of dropout is when the inductor cur-
rent ramps down during the minimum off-time (ΔI
as much as it ramps up during the on-time (ΔI
ratio h = ΔI
to slew the inductor current higher in response to
increased load, and must always be greater than 1. As
h approaches 1, the absolute minimum dropout point,
the inductor current cannot increase as much during
each switching cycle, and V
unless additional output capacitance is used.
A reasonable minimum value for h is 1.5, but adjusting
this up or down allows trade-offs between V
capacitance, and minimum operating voltage. For a
given value of h, the minimum operating voltage can be
calculated as:
where V
path (see the On-Time One-Shot section), t
from the Electrical Characteristics table, and K (1/f
is taken from Table 3. The absolute minimum input volt-
age is calculated with h = 1.
If the calculated V
minimum input voltage, operating frequency must be
reduced or output capacitance added to obtain an
acceptable V
pated, calculate V
response.
SAG
CHG
equation in the Transient Response section).
UP
is the parasitic voltage drop in the charge
V
SAG
/ΔI
IN MIN
(
DOWN
. If operation near dropout is antici-
SAG
______________________________________________________________________________________
IN(MIN)
) =
Dual Quick-PWM Step-Down Controller
to be sure of adequate transient
1
indicates the controller’s ability
−
V
⎛
⎜
⎝
is greater than the required
with Low-Power LDO, RTC Regulator
OUT
h t
×
SAG
OFF MIN
+
K
V
CHG
(
greatly increases
)
⎞
⎟
⎠
SAG
OFF(MIN)
UP
, output
DOWN
). The
SW
is
)
)
Dropout Design Example:
V
f
K = 3.0μs, worst-case K
t
V
h = 1.5:
Calculating again with h = 1 and the typical K-factor
value (K = 3.3μs) gives the absolute limit of dropout:
Therefore, V
very large output capacitance, and a practical input volt-
age with reasonable output capacitance would be 3.47V.
The second output (OUT2) of the MAX17020 works with
applications that require multiple dynamic output volt-
ages, easily supporting two to four output voltages with
external resistors selected by control FETs or REFIN2
can be driven by a DAC for tight voltage control.
Figure 6 shows an application circuit providing four volt-
age levels using discrete components. Switching resis-
tors in and out of the resistor network changes the
voltage at REFIN2. The reference input automatically
detects large input voltage transitions and blanks the
fault and PGOOD2 comparators, allowing the system to
perform the transition without tripping the fault protection.
SW
OFF(MIN)
OUT2
CHG
= 355kHz
= 100mV
= 2.5V
= 500ns
V
IN MIN
V
Dynamic Output Voltage Settings
IN
IN MIN
(
(
must be greater than 3.06V, even with
)
=
)
=
1
−
1
−
2 5
⎛
⎝ ⎜
2 5
MIN
.
1 5 500
⎛
⎝ ⎜
.
.
1 500
V
V
×
3 0
3 3
×
= 3.3μs
+
+
.
.
0 1
0 1
μs
μs
.
.
ns
V
V
ns
⎞
⎠ ⎟
⎞
⎠ ⎟
=
=
3 06 6 V
3. . 47V
.
(OUT2 Only)
29