MAX1586A Datasheet, PDF (27/32 Pages) Maxim Integrated Products – High-Efficiency, Low-IQ PMICs with Dynamic Core for PDAs and Smart Phones

High-Efficiency, Low-I_Q PMICs with
Dynamic Core for PDAs and Smart Phones
Note that the pole cancellation does not have to be
exact. R_C x C_C need only be within 0.75 to 1.25 times
R_LOAD x C_OUT. This provides flexibility in component
selection.
If the output filter capacitor has significant ESR, a zero
occurs at:
Z_ESR = 1 / (2π x C_OUT x R_ESR)
If Z_ESR > f_C, it can be ignored, as is typically the case
with ceramic or polymer output capacitors. If Z_ESR is
less than f_C, it should be cancelled with a pole set by
capacitor C_P connected from CC_ to GND:
C_P = C_OUT R_ESR / R_C
If C_P is calculated to be < 10pF, it can be omitted.
Optimizing Transient Response
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.
Applications Information
Backup-Battery and V7 Configurations
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.
Primary Backup Battery
A connection with a primary (nonrechargeable) lithium
coin cell is shown in Figure 5. 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.
No Backup Battery (or Alternate Backup)
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 6). 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.
Rechargeable Li+ Backup Battery
If more backup power is needed and a primary cell has
inadequate capacity, a rechargeable lithium cell can be
accommodated as shown in Figure 7. A series resistor
and diode charge the cell when the 3.3V V1 supply is
MAIN
POWER
4.7µF
1kΩ
1-CELL
Li+ RECHARGEABLE
BACKUP BATTERY
4.7µF
1µF
IN
MAX1586
MAX1587
V1
BKBT
V7
Figure 7. A 1-cell rechargeable Li+ battery provides more back-
up power when a primary cell is insufficient. The cell is charged
to 3.3V when V1 is active. Alternately, the battery can be
charged from IN if the voltages are appropriate for the cell type.
MAIN
POWER
4.7µF
D1
1N4148
1µF
IN
MAX1586
BKBT ^MAX1587
V7
1-CELL
NiMH
RECHARGEABLE
BACKUP BATTERY
1N4148
4.7µF
10kΩ
MURATA
LQH32C 10µH
BATT
LX
MAX1724
EZK30
SHDN
OUT
GND
10µF
MAIN
POWER
4.7µF
IN
MAX1586
MAX1587
3.0V
BKBT
V7
1µF
Figure 6. BKBT connection when no backup battery is used, or
if an alternate backup scheme, not involving the
MAX1586/MAX1587, is used.
Figure 8. A 1-cell NiMH battery can provide backup by boost-
ing with a low-power DC-DC converter. A series resistor-diode
trickle charges the battery when the main power is on.
______________________________________________________________________________________ 27