SiC461, SiC462, SiC463, SiC464
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S18-0938-Rev. M, 17-Sep-2018 9Document Number: 65124
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Power-Save Mode, Mode Pin, and Ultrasonic Pin Operation
To improve efficiency at light-loads, SiC46x provides a set
of innovative implementations to reduce low side
re-circulating current and switching losses. The internal zero
crossing detector monitors SW node voltage to determine
when inductor current starts to flow negatively. In power
saving mode, as soon as inductor current crosses zero, the
device first deploys diode mode by turning off the low side
MOSFET. If load further decreases, switching frequency is
reduced proportional to the load condition to save switching
losses while keeping output ripple within tolerance. If the
ultrasonic pin is tied to VDD, the minimum switching
frequency in discontinuous mode is > 20 kHz to avoid
switching frequencies in the audible range. If this feature is
not required ultrasonic mode can be disabled by floating the
ULTRASONIC pin. When ultrasonic mode is disabled, the
regulator will operate in forced continuous mode or power
save mode where there is no limit to the lower frequency
limit. In this state, at zero load, switching frequency can go
as low as hundreds of hertz.
To improve the converter efficiency, the user can choose to
disable the internal VDRV regulator by picking either mode 3
or mode 4 and connecting a 5 V supply to the VDRV pin. This
reduces power dissipation in the SiC46x by eliminating the
VDRV linear regulator losses.
The mode pin supports several modes of operation as
shown in table 1. An internal current source is used to set
the voltage on this pin using an external resistor:
Note
(1) Connect a 5 V (± 5 %) supply to the VDRV pin
The mode pin is not latched to any state and can be
changed on the fly.
OUTPUT MONITORING AND PROTECTION FEATURES
Output Over-Current Protection (OCP)
SiC46x has pulse-by-pulse over current limit control. The
inductor current is monitored during low side MOSFET
conduction time through RDS(on) sensing. After a pre-defined
blanking time, the inductor current is compared with an
internal OCP threshold. If inductor current is higher than
OCP threshold, high side MOSFET is kept off until the
inductor current falls below OCP threshold.
OCP is enabled immediately after VDD passes UVLO level.
OCP is set by an external resistor, RLIM to AGND. (See table 2)
Fig. 7 - Over-Current Protection Illustration
Output Undervoltage Protection (UVP)
UVP is implemented by monitoring the FB pin. If the voltage
level at FB drops below 0.16 V for more than 25 µs, a UVP
event is recognized and both high side and low side
MOSFETs are turned off. After a duration equivalent to
20 soft start periods, the IC attempts to re-start. If the fault
condition still exists, the above cycle will be repeated.
UVP is only active after the completion of soft-start
sequence.
Output Over Voltage Protection (OVP)
OVP is implemented by monitoring the FB pin. If the voltage
level at FB rising above 0.96 V, a OVP event is recognized
and both high side and low side MOSFETs are turned off.
Normal operation is resumed once FB voltage drop below
0.91 V.
Over Temperature Protection (OTP)
OTP is implemented by monitoring the junction
temperature. If the junction temperature rises above 150 °C,
a OTP event is recognized and both high side and low
MOSFETs are turned off. After the junction temperature falls
below 115 °C (35 °C hysteresis), the device restarts by
initiating a soft start sequence.
Sequencing of Input / Output Supplies
SiC46x has no sequencing requirements on its supplies or
enables (VIN, VCIN, VDD, VDRV, EN).
Enable
The SiC46x has an enable pin to turn the part on and off.
Driving this pin above 1.35 V enables the device, while
driving the pin below 1.2 V disables the device.
The EN pin is internally pulled to AGND by a 5 M resistor to
prevent unwanted turn on due to a floating GPIO.
Soft-Start
During soft start time period, inrush current is limited and the
output voltage is ramped gradually. The following control
scheme is implemented:
Once the VDD voltage reaches the UVLO trip point, an
internal “Soft start Reference” (SR) begins to ramp up. The
SR ramp rate is determined by the external soft start
capacitor and an internal 5 µA current source tied to the soft
start pin.
The internal SR signal is used as a reference voltage to the
error amplifier (see functional block diagram). The control
scheme guarantees that the output voltage during the soft
start interval will ramp up coincidently with the SR voltage.
The soft-start time, tSS, is adjustable by calculating a
capacitor value from the following equation.
During soft-start period, OCP is activated. Short circuit
protection is not active until soft-start is complete.
TABLE 1 - OPERATION MODES
MODE RANGE (k)POWER SAVE
MODE
INTERNAL VDRV
REGULATOR
1 0 to 100 Enabled ON
2 298 to 304 Disabled ON
3 494 to 504 Disabled OFF (1)
4 900 to 1100 Enabled OFF (1)
Iload
OCPthreshold
Iinductor
GH
tss
Css x 0.8 V
5 µA
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