Datasheet

4
5
6
7
8
3 8 13 18
V -InputVoltage-V
I
Icl-CurrentLimitedThreshold- A
T =-40°C
J
T =25°C
J
T =150°C
J
70
80
90
100
110
120
MinimumControllableOnTime-ns
-50 -25 0 25 50 75 100 125 150
T -JunctionTemperature-°C
J
V =12V,
I =2 A
I
O
3
4
5
6
Dmin-MinimumControllableDutyRatio-%
-50 -25 0 25 50 75 100 125 150
T -JunctionTemperature-°C
J
RT =100k ,
V =12V,
I =2 A
W
I
O
2
2.05
2.1
2.15
2.2
V -BOOT-PHUVLOThreshold- A
boot
m
-50 -25 0 25 50 75 100 125 150
T -JunctionTemperature-°C
J
TPS54320
www.ti.com SLVS982A –AUGUST 2010–REVISED SEPTEMBER 2010
TYPICAL CHARACTERISTICS (continued)
HIGH-SIDE CURRENT LIMIT THRESHOLD vs MINIMUM CONTROLLABLE ON TIME vs
INPUT VOLTAGE TEMPERATURE
Figure 13. Figure 14.
MINIMUM CONTROLLABLE DUTY RATIO vs
JUNCTION TEMPERATURE BOOT-PH UVLO THRESHOLD vs TEMPERATURE
Figure 15. Figure 16.
OVERVIEW
The device is a 17-V, 3-A, synchronous step-down (buck) converter with two integrated n-channel MOSFETs. To
improve performance during line and load transients the device implements a constant frequency, peak current
mode control which also simplifies external frequency compensation. The wide switching frequency of 200 kHz to
1200 kHz allows for efficiency and size optimization when selecting the output filter components. The switching
frequency is adjusted using a resistor to ground on the RT/CLK pin. The device also has an internal phase lock
loop (PLL) controlled by the RT/CLK pin that can be used to synchronize the switching cycle to the falling edge
of an external system clock.
The device has been designed for safe monotonic startup into pre-biased loads. The default start up is when VIN
is typically 4.0V. The EN pin has an internal pull-up current source that can be used to adjust the input voltage
under voltage lockout (UVLO) with two external resistors. In addition, the EN pin can be left floating for the
device to automatically start with the internal pull-up current. The total operating current for the device is
approximately 600mA when not switching and under no load. When the device is disabled, the supply current is
typically less than 2mA.
The integrated MOSFETs allow for high efficiency power supply designs with continuous output currents up to 3
amperes. The MOSFETs have been sized to optimize efficiency for lower duty cycle applications.
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