MAX1586AETM-T Maxim Integrated Products, MAX1586AETM-T Datasheet - Page 27

• Manufacturer Part Number: MAX1586AETM-T
• Description: Other Power Management PMICs w/Dynamic Core for PDAs
• Manufacturer: Maxim Integrated Products

We choose 22µF.
Recalculate R
Note that the pole cancellation does not have to be
exact. R
R
selection.
If the output filter capacitor has significant ESR, a zero
occurs at:
If Z
with ceramic or polymer output capacitors. If Z
less than f
capacitor C
If C
In applications that require load-transient response to
be optimized in favor of minimum component values,
increase the output filter capacitor to increase the R in
the compensation RC. From the equations in the previ-
ous section, doubling the output cap allows a doubling
of the compensation R, which then doubles the tran-
sient gain.
The V3 output can be serially programmed to supply
from 0.7V to 1.475V in 25mV steps. In some cases, a
higher CPU core voltage may be desired. The V3 volt-
age range can be increased by adding two resistors as
shown in Figure 7.
R24 and R25 add a small amount of gain. They are set
so that an internally programmed value of 1.475V
results in a higher actual output at V3. The resistors
shown in Figure 7 set a maximum output of 1.55V, 1.6V,
or 1.65V. All output steps are shifted and the step size
is also slightly increased.
The output voltage for each programmed step of V3 in
Figure 7 is:
where V3 is the actual output voltage, V3
original programmed voltage from the "OUTPUT (V)"
LOAD
ESR
P
is calculated to be < 10pF, it can be omitted.
x C
> f
V3 = V3
(V3
C
x C
C
C
R
OUT
PROG
P
, it should be cancelled with a pole set by
, it can be ignored, as is typically the case
C
Z
connected from CC_ to GND:
C
Dynamic Core for PDAs and Smart Phones
C
ESR
= C
. This provides flexibility in component
Applications Information
using the selected C
PROG
need only be within 0.75 to 1.25 times
C
/185.5kΩ)]
Extending the Maximum Core
______________________________________________________________________________________
OUT
P
= 1/(2π x C
= C
Optimizing Transient Response
+ R24[(V3
x R
OUT
LOAD
x R
OUT
High-Efficiency, Low-I
/C
ESR
PROG
C
x R
/R
= 208kΩ
OUT
Voltage Range
C
/R25) +
ESR
.
)
PROG
ESR
is the
is
column in Table 2, and 185.5kΩ is the internal resis-
tance of the FB3 pin.
The MAX1586/MAX1587 include a backup-battery con-
nection, BKBT, and an output, V7. These can be utilized
in different ways for various system configurations.
A connection with a primary (nonrechargeable) lithium
coin cell is shown in Figure 6. The lithium cell connects to
BKBT directly. V7 powers the CPU VCC_BATT from either
V1 (if enabled) or the backup battery. It is assumed
whenever the main battery is good, V1 is on (either with
its DC-DC converter or sleep LDO) to supply V7.
If no backup battery is used, or if an alternate backup
and VCC_BATT scheme is used that does not use the
MAX1586/MAX1587, then BKBT should be biased from
IN with a small silicon diode (1N4148 or similar, as in
Figure 8). BKBT must still be powered when no backup
battery is used because DBO, RSO, and POK require
this supply to function. If BKBT is not powered, these
outputs do not function and are high impedance.
Figure 7. Addition of R24 and R25 increases maximum core
voltage. The values shown raise the maximum core from
1.475V to 1.55V.
Backup-Battery and V7 Configurations
**OTHER R24 VALUES:
R24 = 5.5kΩ, V3: 0.759V TO 1.60V
R24 = 7.7kΩ, V3: 0.783V TO 1.65V
STEP-DOWN
No Backup Battery (or Alternate Backup)
PWM
REG3
MAX1586
MAX1587
185.5kΩ
Q
PV3
PG3
LX3
FB3
PMICs with
Primary Backup Battery
TO BATT
3.3kΩ
R24**
R25
100kΩ
V3
VCC_CORE
1.55V MAX
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