TPS2306 Datasheet, PDF (15/28 Pages) Texas Instruments – DUAL SEQUENCING HOT SWAP POWER MANAGER

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TPS2306
DUAL SEQUENCING HOT SWAP POWER MANAGER
APPLICATION INFORMATION
SLVS368 – APRIL 2001
140
6
IREF = 100 µA
120
ENABLE
5
100
4
80
3
60
2
40
GATE1
20
1
IMAX1 Current
0
0
t0 t1 _{t – Time} t2
Figure 5. TPS2306 Typical IMAX1 Turn–on
Sequence
Output Voltage
t1 t2
t3
t4 t5
t – Time
Figure 6. TPS2306 Slow Ramp Operation
In Figure 5, the channel 1 ramp-up conditions are met at time t₀ = 0. This means that the ENBL input is asserted,
both supply input and charge pump UVLO conditions are met, and the UP1 input voltage exceeds the 1.5-V
threshold. After a nominal delay, the IMAX1 current sink is turned on at t₁, but only at a level that is approximately
5% of the programmed IMAX level. This stage typically lasts approximately 500 µs. After about 500 µs at t₂, the
IMAX1 current ramps to the full programmed level (≅I_REF).
The same two-step characteristic is also used to turn-on the channel 2 FET.
From the load’s perspective, the slow turn-on of the pass elements has the effect shown in Figure 6.
Figure 6 shows the GATE1 and output voltage response to the typical IMAX1 ramp shown in Figure 5. In this
example, the FET is driving an RC-type load. At time t₁, the IMAX1 input is turned on at a magnitude of ≅I_SNK/20.
The GATE1 output begins to drive the FET gate. However, the FET remains OFF initially, and no current is
allowed to flow. At t₂ the gate voltage exceeds the V_GS(on) threshold of the FET. Between t₂ and t₃ the output
current is limited to the slow turn-on level established by the TPS2306. Accordingly, only slight charging of the
output is obtained during this period. At t₃, the slow ramp time period expires (the current at IMAX1 steps to the
programmed level) and the output now charges at a rate of IMAX/C_LOAD1. As the output voltage approaches
the input supply level around time t₄, the charging current begins to taper toward the steady-state load level.
The GATE1 output then drives towards the charge pump voltage, thus fully enhancing the external pass FET.
By time t₅, the output has charged up to 95% of the input dc potential.
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