I'm having difficulty getting the TI TPS53353 switching regulator working. I designed the circuit to produce a 5V output from a 15V input. Here are pictures of the schematic and layout (0804.TPS53353.pdf). The layout shows the top and bottom layers, there are also an internal ground plane and an internal layer for +5V_Fused (connected to vias on output of fuse F3) that are not shown. Values of the passive components were calculated using the table below.
When I supplied the 15V the regulator's output was fluctuating when observed on a voltmeter and there was audible clicking coming fromt the chip. After about 30 sec of being powered, a bit of fire and then smoke came out of the chip and I quickly shut off the 15V supply.
The ceramic caps are all X5R/X7R. Could the problem be that the capacitor values are too far off? Should I be using C0G/NP0 caps?
The outout electrolytic caps used have an ESR of 13 mOhm (6.5 mOhm in ||), but the design originally specified using caps with an ESR of 17 mOhm (8.5 mOhm in ||), as listed in the excel file). Could a too low ESR cause stability issues?
After the chip popped, it was removed and pins 19 (VDD) and 20 (MODE) were seen to be blown off the chip and their pads where blown off the board. With the board as it is now, pins 19 and 20 are shorted, but that may have happened when the chip blew. If they were shorted to start with, could that have caused the chip to blow?
Any other thoughts on what might be wrong with my design?
Thank you.
| TPS53355 Component Values | ||||
| Parameter | Value | Description | Datasheet Location | Notes |
| Vin (V) | 15 | Input voltage | ||
| Vout (V) | 5 | |||
| Imax (A) | 20 | Maximum load current | ||
| Iocp (A) | 25 | Over-current protection threshold | ||
| Fsw (Hz) | 500000 | Switching frequency | Table 2 (p.16) | |
| Rrf (Ohms) | Open | Fsw select resistor | Table 2 (p.16) | |
| R2 (Ohms) | 10000 | Output voltage set resistor 2 | ||
| Rmode (Ohms) | 39000 | Mode set resistor | Table 1 (p. 15) | Connect to ground |
| Rds (Ohms) | 0.0016 | Internal switch resistance @ Iocp | Step 6 (p. 21) | |
| Itrip (A) | 0.00001 | Current through Rtrip @ Iocp | Step 6 (p. 21) | |
| Ideal Values | Formula | |||
| Iripple (A) | 6.666666667 | Inductor ripple current | Step 3 (p. 20) | Iripple = Imax/3 |
| L (H) | 1.00E-06 | Inductor value | Eq. 6 (p. 20) | L = (3/(Imax*Fsw))*((Vin - Vout)*Vout/Vin) |
| Vtrip (V) | 1.109333333 | Voltage on Rtrip @ Iocp | Eq. 3 (p. 18) | Vtrip = 16*Rds*(2*Iocp - Iripple) |
| Rtrip (Ohms) | 110933.3333 | Rtrip value | Eq. 2 (p. 18) | Rtrip = Vtrip/Itrip |
| Ipk (A) | 28.33333333 | Peak inductor current | Eq. 7 (p. 20) | Ipk = Vtrip/(32*Rds) + (1/(L*Fsw))*((Vin - Vout)*Vout/Vin) |
| ESR (Ohms) | 0.008333333 | Ouput capacitor ESR | Eq. 8 (p. 20) | ESR = L*Fsw/60 |
| R1 (Ohms) | 72870.37037 | Output voltage set resistor 1 | Eq. 9 (p. 20) | R1 = (Vout - (Iripple*ESR/2) - 0.6)*R2/0.6 |
| Real Values - Calculated using component values | ||||
| L (H) | 9.60E-07 | Inductor value | Vishay Dale | IHLP5050FDER1R0M01 |
| ESR (Ohms) | 0.0085 | Ouput capacitor ESR (2 in parallel) | Nichicon | RHT1A331MDN1 |
| Rtrip (Ohms) | 110000 | Rtrip value | ||
| R1 (Ohms) | 73200 | Output voltage set resistor 1 | ||
| R2 (Ohms) | 10000 | Output voltage set resistor 2 | ||
| Rrf (Ohms) | Open | Fsw select resistor | ||
| Vout (V) | 5.020333333 | Output voltage | Eq. 9 (p. 20) | Vout = (R1*0.6/R2) + (Iripple*ESR/2) + 0.6 |
| Vtrip (V) | 1.1 | Vtrip value | Eq. 2 (p. 18) | Vtrip = Itrip*Rtrip |
| Ipk (A) | 28.42881944 | Peak inductor current | ||