ncp1578 ON Semiconductor, ncp1578 Datasheet - Page 14

• Manufacturer Part Number: ncp1578
• Description: Synchronous Step Down Controller With 50ma Linear Regulator
• Manufacturer: ON Semiconductor

SMPS is disabled by EN_SW. Note that the PGOOD pin is
valid providing LDO5 is high enough to maintain the
internal logic state.
Overvoltage Protection
preset nominal regulation voltage for 16 consecutive
internal clock cycles, the SMPS output will be latch off and
it can be restarted by toggling EN_SW or LDO5.
Undervoltage Protection
regulation voltage for 16 consecutive internal clock cycles,
the undervoltage fault is set, the SMPS is latched off.
4. External +5 V is connecting to V
5. For this configuration, it is recommended to pull EN_LDO to GND at any time.
OPERATION TABLE 1
OPERATION TABLE 2
When SMPS output voltage is above 115% (typ) the
When SMPS output falls below 65% (typ) of the nominal
FPWM
FPWM
High
High
Low
Low
X
X
X
Input Condition
Input Condition
EN_LDO
EN_LDO
(Note 5)
High
High
High
Low
Low
Low
Low
(Single Supply V
(External +5 V and V
EN_SW
EN_SW
High
High
High
High
Low
Low
X
BAT
and LDO5 pin.
BAT
On (DCM or Pulse Skipping)
Configuration)
IN
Configuration (Note 4))
On (FPWM)
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SMPS
Off
Off
On (DCM or pulse skipping)
NCP1578
Operating Condition
Operating Condition
14
On (FPWM)
Cycling EN_SW or LDO5 can reset the undervoltage fault
latch and restart the controller.
Soft-Start
the device to prevent surge current from power supply and
output voltage overshot during power up. When EN_SW,
LDO5 rises above their respective upper threshold voltages,
the external soft start capacitor C
current source I
V
time Tss can be programmed by the soft-start capacitor
according to the following equation: T
SMPS
ref
Off
The switcher V
voltage, the soft start process is finished. The soft-start
ss
. When the soft-start voltage reaches the
OUT
LDO5
Off
On
On
On
soft-start feature is incorporated in
ss
is charged by a constant
ss
Output Condition
Output Condition
[ (0.8 x C
PGOOD
PGOOD
H-Z
H-Z
H-Z
H-Z
H-Z
Low
Low
ss
) / I
ss
.