V – Input Voltage – V

I

7

8

9

10

11

3

8

13

18

T = –40 C

J

°

T = 25 C

J

°

T = 125 C

J

°

T – Junction Temperature – C

J

°

70

80

90

100

110

–50

–25

0

25

50

75

100

125

120

VIN = 12 V

IOUT = 2 A

T – Junction Temperature – C

J

°

3

4

5

6

–50

–25

0

25

50

75

100

125

RT = 100 K

VIN = 12 V

IOUT = 2 A

150

T – Junction Temperature – C

J

°

2.0

2.1

2.2

–50

–25

0

25

50

75

100

125

TPS54521

SLVS981 – JUNE 2010

www.ti.com

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, 5-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

900 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 5

amperes. The MOSFETs have been sized to optimize efficiency for lower duty cycle applications.

10

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