MIC7400_15 Datasheet, PDF (31/68 Pages) Micrel Semiconductor – Configurable PMIC, Five-Channel Buck Regulator Plus One-Boost with HyperLight Load® and I2C Control

Micrel, Inc.
Stand-By Mode
In stand-by mode, efficiency can be improved by lowering
the output voltage to the standby mode value or turning
an output off completely. There are two registers used for
setting the output voltage, normal-mode register and
stand-by mode register. The default power-up voltages
are set in the normal-mode registers.
An I²C write command to the STBY_CTRL_REG register
or the STBY pin can be used to set the MIC7400 into
stand-by mode. Figure 12 shows an I²C write command
implementation. In stand-by mode, the output can be
programmed to a lower voltage or turned completely off.
When disabled, the output will be soft-discharged to zero
if the PULLD[1-6] register are set to 1. If PULLD[x] = 0
the output drifts to PGND at a rate determined by the
load current and output capacitance.
In stand-by, if an output is disabled, the global power
good output is not affected when the PGOOD_MASK[x]
is set to logic 1. If the PGOOD_MASK[x] is set to logic 0,
then the global power good flag is pulled low. In Figure
12, all the PGOOD_MASK[x] bits are set to logic 1.
MIC7400
Resistive Discharge
To ensure a known output condition in stand-by mode,
the output is actively discharged to ground if the output is
disabled. Setting the buck pull down register field
PULLD[1-5] = 1 connects a 90Ω pull down resistor from
OUT[x] to PGND[x] when the MIC7400 is disabled. If
PULLD[x] = 0 the output drifts to PGND at a rate
determined by the load current and the output
capacitance value. The boost has a programmable pull-
down current level from 37mA to 148mA. In Figure 13,
the top trace shows the normal pull down and the bottom
trace is with the 90Ω pull-down.
Figure 12. I²C Stand-By Mode
March 3, 2015
Figure 13. Output Pull-Down Resistance
STBY Pin
A pin-selectable STBY input allows the MIC7400 to be
placed into standby or normal mode. In standby mode,
the individual regulator can be turned on or off or the
output voltage can be set to a different value. If the
regulators are turned off, standby mode cuts the
quiescent current by 23µA for each buck regulator and
70µA for the boost.
Figure 14 illustrates the STBY pin operation. A low-to-
high transition on the STBY pin switches the output from
standby mode to normal mode. There is a 100µs STBY
deglitch time to eliminate nuisance tripping then all the
regulators are enabled at the same time and ramp up
with their programmed ramp rates. A high-to-low
transition on the STBY pin switches the output from
normal mode to standby mode.
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Revision 2.0