ML486:
FUNCTIONAL DESCRIPTION
roWER DOWN MODES
BUCK REGULATORS
The two buck regulators (Figure 1) are synchronously
rectifying voltage mode PWM regulators capable of bein
used over a wide variety of loads and input voltages. Th
use of synchronous rectification improves system
efficiency by reducing the fixed drop associated with the
"free-wheeling" diode in conventional regulators. These
regulators drive all N-channel power MOSFETs, to achie
lowest
RDSION)
at the lowest cost. In order to drive the
MOSFET gates adequately, a Vcr supply must be
provid~
which is higher than the battery voltage by an amount
sufficient to provide full enhancement voltage to the
MOSFETs. This can be generated by using a winding fror
the 5V buck regulator as shown in Figure 2. Vcr must nil
be lower than O.5V below VIN.
1/
The
Ml4862
operates in either a powered down mode or
un mode according to the state of the ON/OFF pin
ble 1). When the ON/OFF pin is high, the
Ie
is in the
I
~
mode and the various IC sections are functioning
~cording
to the logic
~h?wn
in Table 1. When the ON/
OFF
pin is low, the IC
IS
rn the standby mode and only the
power 5V linear regulator and
2.5~
reference are on. All
~ate
drive outputs are low. The 5V linear regulator then
~vides
the power to run the system's power
management logic.
TABLE 1. ML4862 POWER DOWN MODES
MODE
ONIOO
0
1
1
ENABLE A
ONIOO12
FUNCTION
Micro Power 5V Reg Only
12V linear Regulator on
Synchronous Rectifier Drive for Reg. A Disabled,
All Other Functions Running
All Functions Enabled
TOTALSUPPLj
CURRENT
l30llA
600 A
8mA
lOmA
Sleep
12V
Partial
X
X
0
X
1
0
0
Run
Run
RT
OSCILLATOR
Fl
Q
RFI
Rl C1
COMP
RF2
Ql l - - - - - - - - - 1 Q
F2
sl-----<
• Buck R"8""'lo,
It.
only
Figure1. BuckRegulatorBlock Diagram.
MICRO-LINEAR [ MICRO LINEAR CORPORATION ]
