TPS51020

SLUS564B − JULY 2003 − REVISED DECEMBER 2003

6

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ELECTRICAL CHARACTERISTICS (continued)

TA = −40°C to 85°C, 4.5 V < VIN < 20 V, CVIN = 0.1 µF, CVREG5 = 2.2 µF, CREF_X = 0.01 µF, PGOOD = 0.2 V, ENBLx = DDR = VIN,

INVx = COMPx, RSSTRTx = OPEN, TRIP1 = TRIP2 = VIN, LLx = GND, VBSTx = LLX+5, C(OUTx_U, OUTx_D)=1 nF, REG5_IN = 0V, GND =

OUTGNDx = 0 V, VO1_VDDQ = VO2 = 0 V (unless otherwise stated)

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

TIMERS: SOFT-START RAMP GENERATOR

ISSQ

SSTRTx charge current

VSSTRTx = 1 V

1.8

2.3

2.9

µA

ISSDQ

SSTRTx discharge current

VSSTRTx = 0.5 V

0.1

mA

VREFTRK

SSTRTx at SMPS regulation point voltage(7)

1.00

1.22

1.45

VSSOK

SSTRTx OK to restart voltage

0.23

0.29

0.35

V

VSSFIN

SSTRTx finished voltage(8)

1.4

1.5

1.6

V

VSSCLP

SSTRTx frequency select voltage(9)

3.35

3.60

3.80

OUTPUTS: INTERNAL BST DIODE

VFBST

Forward voltage

(VVREF5− VVBSTx),VVREF5 = 5 V, IF = 10 mA

TA = 25°C

0.80

0.85

V

IRBST

Reverse current

VRBST= 30 V

0.1

0.5

µA

OUTPUTS: N-CHANNEL MOSFET GATE DRIVERS

RUSRC

OUTx_U source impedance

3

10

RDSRC

OUTx_D source impedance

3

10

Ω

RUSNK

OUTx_U sink impedance

2.5

5.0

Ω

RDSNK

OUTx_D sink impedance

2.5

5.0

TDEAD

Gate non-overlap dead time

100

ns

(1) Ensured by design. Not production tested.

(2) Maximum 450-kHz frequency can be achieved only when both channels are enabled.

(3) 270 kHz is the default frequency during start-up for both channels.

(4) See Table 1.

(5) See PWM detailed description

(6) Feedforward Gain can be approximated as follows:

VRAMP= K1×VIN+B1, VOFFSET=K2×VIN×+B2 where K1=0.017, K2=0.01, B1=0.35 V, B2=0.4 V.

K1

) B1

VIN

) (K2

VIN

) B2)

(7) See waveform point A in Figure 1

(8) See waveform point B in Figure 1

(9) See waveform point C in Figure 1

Table 1. Frequency Selection

SSTRT1

SSTRT2

FREQUENCY (kHz)

CSSTRT only

CSSTRT only

450(10)

1 M

Ω || CSSTRT to GND

CSSTRT only

360

CSSTRT only

1 M

Ω || CSSTRT to GND

360

1 M

Ω || CSSTRT to GND

1 M

Ω || CSSTRT to GND

270

(10)Although selection is made by placing a 1M resistor in parallel with the SSTRTx timing

capacitor, the softstart time to 0.85V is altered by about only 20%.