Texas Instruments LM34904EVM Evaluation Module LM34904EVM/NOPB LM34904EVM/NOPB Datenbogen
Produktcode
LM34904EVM/NOPB
Evaluation Module Component Selection
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Evaluation Module Component Selection
Ceramic input and output capacitors are positioned close to the load switch. Specifically, two 22 µF
bypass capacitors from VCC to GND minimize input voltage drop during a high current startup event or
momentary output short circuit condition. A 1 µF capacitor is usually adequate even though larger
capacitance will further reduce the voltage drop. A 4.7 µF decoupling capacitor from ACC_PWR to GND
alleviates any negative swing of ACC_PWR induced by parasitic inductance in the load lines as the load
current ramps to zero during a turn-off event. Of course, all traces short be kept as short as possible with
VCC, ACC_PWR and GND power bus traces kept wide to minimize conduction drop and assist with
thermal spreading.
bypass capacitors from VCC to GND minimize input voltage drop during a high current startup event or
momentary output short circuit condition. A 1 µF capacitor is usually adequate even though larger
capacitance will further reduce the voltage drop. A 4.7 µF decoupling capacitor from ACC_PWR to GND
alleviates any negative swing of ACC_PWR induced by parasitic inductance in the load lines as the load
current ramps to zero during a turn-off event. Of course, all traces short be kept as short as possible with
VCC, ACC_PWR and GND power bus traces kept wide to minimize conduction drop and assist with
thermal spreading.
When the output is short-circuited, the input voltage appears across the switch, and the instantaneous
power dissipation can be quite high. If the fault condition is not removed, the die temperature may
increase to the level where the thermal shutdown protection activates. If the faulted short-circuit condition
persists and the device engages thermal shutdown, it latches off. ENABLE can be cycled to initiate a re-
start.
power dissipation can be quite high. If the fault condition is not removed, the die temperature may
increase to the level where the thermal shutdown protection activates. If the faulted short-circuit condition
persists and the device engages thermal shutdown, it latches off. ENABLE can be cycled to initiate a re-
start.
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Evaluation Module Power Up Procedure
Step 1: Apply an input voltage between 2.8V and 5.3V (VCC to GND).
Step 2: Connect ACC_DET to GND.
Step 3: Connect ENABLE to VCC. The load switch turns on – measure voltage from ACC_PWR to GND.
Step 4: Apply a load current up to the rated current of the device – check voltage from ACC_PWR to
GND.
GND.
Step 5: Apply and remove an overload or short circuit – confirm recovery from this condition.
Step 6: Cycle ENABLE high and low to assess turn on and turn off wavefroms, respectively.
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Evaluation Module Performance Characteristics
Using the LM34904 with ACC_DET and POK pullup resistors connected to a pullup voltage source of
1.8V, various performance characteristics of the evaluation module are presented in
1.8V, various performance characteristics of the evaluation module are presented in
through
Figure 3. ENABLE Turn On, VCC = 2.8V, IOUT = 0.5A
Figure 4. ENABLE Turn On, VCC = 5.3V, IOUT = 0.5A
(Resistive Load)
(Resistive Load)
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AN-2266 LM34902/4 Current Limited Power Switch Evaluation Module
SNVU156A – July 2012 – Revised May 2013
Copyright © 2012–2013, Texas Instruments Incorporated