ncp1508 ON Semiconductor, ncp1508 Datasheet - Page 11

• Manufacturer Part Number: ncp1508
• Description: Up To 500 Ma, 1 Mhz, High Efficiency Synchronous Stepdown Dcdc Converter In Dfn Package
• Manufacturer: ON Semiconductor

Output Voltage Selection
four voltage levels depending on the logic state of CB0 and
CB1. Therefore if the NCP1508’s load, such as a digital
cellular phone’s baseband processor, supports dynamic
power management, the device can lower or raise its core
voltage under software control. When combined with the
pulsed current mode function in low load situations, this
active voltage management further stretches the useful
operating life of the handset between charges. Figure 24
shows a typical transition between 1.5 to 1.89 volts.
has a pull down resistor and the CB1 has a pullup resistor.
The default output voltage is 1.3 V when CB0 and CB1 are
floating.
Table 1. Operating Mode Selection
Table 2. Truth Table for CB0 and CB1 with the
corresponding output voltage
LOW
HIGH
CLOCK
The output voltage is digitally programmed to one of
The output voltage levels are listed in Table 2. The CB0
SYNC Pin State
CB0
0
0
1
1
Pulsed Mode (PM)
PWM, 1 MHz Switch Frequency
PWM, Frequency Synchronization
CB1
0
1
1
0
Operating Mode
Vout(V)
1.89
1.0
1.3
1.5
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11
Soft−Start
when the device is initially powered up or enabled.
Soft−start is implemented by gradually increasing the
reference voltage until it reaches the full reference voltage.
During startup, a pulsed current source charges the internal
soft−start capacitor to provide gradually increasing
reference voltage for the PWM loop. When the voltage
across the capacitor ramps up to the nominal reference
voltage, the pulsed current source will be switched off and
the reference voltage will switch to the regular reference
voltage. From Figure 21, it show the soft−start time is about
1.5 ms.
Shutdown Mode
0.4 V, the NCP1508 will be disabled. In shutdown mode,
the internal reference, oscillator and most of the control
circuitries are turned off. Therefore, the typical current
consumption will be 0.1 mA (typical value).
the device for normal operation. The device will go through
soft−start to normal operation.
Thermal Shutdown
protect the integrated circuit in the event that the maximum
junction temperature is exceeded. If the junction
temperature exceeds 160°C, the device shuts down. In this
mode switch Q1 and Q2 and the control circuits are all
turned off. The device restarts in soft−start after the
temperature drops below 135_C. This feature is provided
to prevent catastrophic failures from accidental device
overheating and it is not intended as a substitute for proper
heatsinking.
The NCP1508 uses soft−start to limit the inrush current
When the SHD pin has a voltage applied of less than
Applying a voltage above 1.2 V to SHD pin will enable
Internal Thermal Shutdown circuitry is provided to