MIC7401 datasheet(31/68 Pages) MICREL

31 / 68 page

Micrel, Inc.

MIC7401

March 16, 2015

Revision 1.0

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 MIC7401 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.

Figure 12. I

2C Stand-By Mode

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 MIC7401 is disabled. If

PULLD[x] = 0 the output drifts to PGND at a rate

determined

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 13. Output Pull-Down Resistance

STBY Pin

A pin-selectable STBY input allows the MIC7401 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.

high-to-low

transition on the STBY pin switches the output from

normal mode to standby mode.

MIC7401 Datasheet(PDF) 31 Page - Micrel Semiconductor

MIC7401 Datasheet(HTML) 31 Page - Micrel Semiconductor

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