Datasheet

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SLVS426 − MAY 2002
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10
DEAD-TIME
The internally defined dead-time prevents shoot-through-current flowing through the main power MOSFETs during
switching transitions. Typical value of the dead-time is 100 ns.
STANDBY
The SBRC controller, the LDO controller, and the internal regulators can be switched into standby mode separately as
shown in Table 1. The standby mode current, when both controllers and regulators are off, can be as low as 1 nA.
Table 1. Standby Logic
INPUT FUNCTION
STBY_VREF5 SS_STBYx STBY_VREF3.3 STBY_LDO V
(REG5V_IN)
> 4.5V VREF5 VREF3.3 SBRCx LDO
L L L L False OFF OFF OFF OFF
L
(1)
L
(1)
L
(1)
L
(1)
True
(1)
ON
(1)
OFF
(1)
OFF
(1)
OFF
(1)
H L L L x ON OFF OFF OFF
L H L L x OFF OFF OFF OFF
H H L L x ON OFF ON OFF
L L H L x ON ON OFF OFF
H L H L x ON ON OFF OFF
L H H L x ON ON OFF OFF
H H H L x ON ON ON OFF
L L L H x ON OFF OFF ON
H L L H x ON OFF OFF ON
L H L H x ON OFF OFF ON
H H L H x ON OFF ON ON
L L H H x ON ON OFF ON
H L H H x ON ON OFF ON
L H H H x ON ON OFF ON
H H H H x ON ON ON ON
(1)
This functional mode is not recommended.
x = true or false
SOFT START
Soft start ramp up of the SBRC is controlled by the SS_STBYx pin voltage, which is controlled by an internal current source
and an external capacitor connected between the SS_STBYx and GND pins. When the STBY_VREF5 and/or SS_STBYx
pin voltages are forced to LOW, the SBRCx is disabled. When the STBY_VREF5 pin voltage is set to HIGH and the
SS_STBYx pin floats, the internal current source starts to charge the external capacitor. The output voltage ramps up as
the SS_STBYx pin voltage increases from 0 V to 0.85 V. The soft start time is easily calculated from the supply current and
the capacitance value (see application information). The soft start timing circuit for the LDO is integrated into the device.
The soft start time is fixed and can be as short as 600 µs. This is observed when the LDO is turned on separately from the
SBRC. Simultaneous start-up of one of the SBRC and the LDO, is also possible. Tie the LDO input to the SBRCx’s output,
let both the STBY_VREF5 and STBY_LDO voltages rise to the HIGH level, and invoke Soft start on the SS_STBYx pin;
then the LDO’s output follows the ramp of the SBRCx’s output.