TPS2346

SLUS529 – MAY 2002

21

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APPLICATION INFORMATION

UDG–02005

t1: Slow turn-on period

t2: Linear current ramp (di/dt)

t3: Constant-current load charging

tCHG: IRAMP capacitor charge time, (1.4 × CIRAMP/58)

t1

t2

t3

0 V

VIN

0 A

IIMAX

0 V

0 V

1.5 V

TIME

IRAMP

VOLTAGE

GATE

VOLTAGE

LOAD

CURRENT

BACK–END

VOLTAGE

tCHG

32 x tCHG

Figure 20. Load Current at Startup

Once the slow ramp period has expired, the clamp is removed, and the IRAMP voltage continues to ramp up

at a constant rate of:

I

O

C

IRAMP

+

58

mA

C

IRAMP

Since the linear amplifier acts to maintain equal voltages at its inputs (see Figure 2), it slews the GATEx output

such that the CSx voltage tracks the internally generated reference at its inverting input. Therefore, the linear

voltage ramp at the IRAMP pin results in a linear current ramp to the three positive loads.