Datasheet

TPS54478
SLVSAS2 –JUNE 2011 www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
T
J
= –40°C to 150°C, VIN = 2.95 to 6 V (unless otherwise noted)
DESCRIPTION CONDITIONS MIN TYP MAX UNIT
CURRENT LIMIT
Current limit threshold VIN = 6V, Fs = 500 KHz 5.2 6.5 8.2 A
Cycles before entering hiccup 512 Cycles
Cycles of converter in off state during hiccup 16384 Cycles
Low side Fet reverse current limit 3.1 A
THERMAL SHUTDOWN
Thermal shutdown 165 °C
Hysteresis 15 °C
TIMING RESISTOR AND EXTERNAL CLOCK (RT/CLK PIN)
Switching frequency range using RT mode 200 2000 kHz
Switching frequency R
(RT/CLK)
= 78.7 kΩ 400 500 600 kHz
Switching frequency range using CLK mode 300 2000 kHz
Minimum CLK pulse width 75 ns
RT/CLK voltage R
(RT/CLK)
= 78.7 kΩ 0.5 V
RT/CLK high threshold 1.6 2.2 V
RT/CLK low threshold 0.4 0.6 V
RT/CLK falling edge to PH rising edge delay Measure at 500 kHz with RT resistor in series 75 ns
PLL lock in time Measure at 500 kHz 14 μs
PH (PH PIN)
Measured at 50% points on PH, VIN = 5 V, I
OUT
= 2 A 100
Minimum On time ns
Measured at 50% points on PH, VIN = 5 V,
120
I
OUT
= 0 A
Prior to skipping off pulses, VIN = 5 V,
Minimum Off time 110 ns
I
OUT
= 2 A
Rise Time 1.5
VIN = 5 V, 4 A V/ns
Fall Time 1.5
BOOT (BOOT PIN)
BOOT Charge Resistance VIN = 5 V 15 Ω
BOOT-PH UVLO VIN = 2.95 V 2.2 V
SLOW START AND TRACKING (SS/TR PIN)
SS voltage threshold (V
SSTHR
) 0.15 V
Charge Current V
(SS/TR)
< V
SSTHR
45 μA
V
(SS/TR)
> V
SSTHR
2.2
SS/TR to VSENSE matching V
(SS/TR)
= 0.3 V 65 mV
SS/TR to reference crossover 98% normal 0.86 V
SS/TR discharge voltage (Overload) VSENSE = 0 V 2.5 mV
SS/TR discharge current (Overload) VSENSE = 0 V, V
(SS/TR)
= 0.4 V 900 µA
SS discharge current (UVLO, EN, Thermal
VIN = 5 V, V(SS) = 0.5 V 1.16 mA
fault)
POWER GOOD (PWRGD PIN)
VSENSE falling (Fault) 93
VSENSE rising (Good) 95
VSENSE threshold % Vref
VSENSE rising (Fault) 107
VSENSE falling (Good) 105
Hysteresis VSENSE falling 2 % Vref
Output high leakage VSENSE = VREF, V
(PWRGD)
= 5.5 V 7 nA
On resistance VIN = 2.95 V 56 120 Ω
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