ncp1509 ON Semiconductor, ncp1509 Datasheet - Page 11

• Manufacturer Part Number: ncp1509
• Description: Up To 500 Ma, 1 Mhz, High Efficiency Synchronous Step-down Dc-dc Converter In Dfn Package
• Manufacturer: ON Semiconductor

Output Voltage Selection
voltage levels depending on the logic state of CB0 and CB1.
Therefore if the NCP1509’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 1.57 to 1.8 volts.
has a pull down resistor and the CB1 has a pullup resistor.
The default output voltage is 1.35 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 four
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)
1.05
1.35
1.57
1.8
http://onsemi.com
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 NCP1509 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).
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 NCP1509 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 the
Internal Thermal Shutdown circuitry is provided to