TPL7407L Duty cycle

Alpha,

The chart applies between roughly 500 Hz and 50 kHz. At higher frequency switch losses must be considered. At lower frequencies there will be some heating and cooling at the switching frequency.

In the example is cycle '36mS of two channels on then 36mS of just one channel on' repeated continuously?

Hi Ron

Thank you for your reply.
We got their use case as follow.

        |-> Start up            |-> Normal Operation
ch1     ON      ON      ON      OFF     OFF     OFF     OFF
ch2     ON      ON      ON      ON      ON      OFF     OFF
ch3     OFF     OFF     OFF     OFF     ON      ON      ON
ch4     OFF     OFF     OFF     OFF     OFF     OFF     ON

    (1mass 12ms , 400mA/ch)

Condition
1. They assume using TPL7407L as stepping motor driver.

2. In start up,36ms of 2ch is on state and drive current is 400mA/ch.

3. In normal operation , cycle is 12ms of 2ch on then 12ms of just 1ch on repeated continuously.

Question
1. Is TPL7407L be able to use in their condition?
2. If not , are there any proposal?

Best regards.

Alpha,

Yes, TPL7407 can be used. Figure shows 400mA * 2 channels is good up to TA = 55C. Because sometimes it's only one channel being used Ta can be higher.

For even better performance use two drivers per phase on 3 phases and the one driver on the fourth motor phase (use all 7 channels).

Hi Ron

Thank you for your reply.

Our customer is considering your following proposal.

～your proposal～
--------
For even better performance use two drivers per phase on 3 phases and the one driver on the fourth motor phase (use all 7 channels).
--------

In your proposal,they think hardest condition of thermal is driving current to 2phase coil using 2ch+1ch.

How should they consider thermal condition using Fig5～8?

For example

1. Should they evaluate 1ch drive current?
-> In this case,they evaluate as 400mA.

2. Should they evaluate 2ch+1ch current per phase?
-> In this case,since loss is 3/4 against 1ch+1ch,they can evaluate as current is 3/4?

Additional condition is Ta=70℃

Best regards.

Alpha,

Let's try a worst case scenario.
Data sheet show maximum VOL for 200mA as 650mV.
There is no 400mA limit, so I extrapolate as 400mA as 1320mV maximum.

Worst load case (1CH@400mA + 2CH@200mA)
Power dissipation is 1* 400mA * 1320mV + 2 * 200mA * 650mV = 788mW
Junction temperature = 70C + 788mW * 92C/W = 142.5C
This is close to absolute maximum temperature.
However, this is worst case for just 1 of 8 stepping patterns.

For 1CH@400mA
Power dissipation is 1* 400mA * 1320mV = 528mW
Junction temperature = 70C + 528mW * 92C/W = 118.6C

For 2CH@200mA
Power dissipation is 2* 200mA * 650mV = 260mW
Junction temperature = 70C + 260mW * 92C/W = 94C

For 2CH@200mA + 2CH@200mA
Power dissipation is 2* 200mA * 650mV * 2 = 520mW
Junction temperature = 70C + 520mW * 92C/W = 118C

Averaging the temperatures for alll steps gives (2*142.5C + 118.6C + 3 * 194C + 2 * 118C) / 8 = 115.2C

A worst case motor running temperature of 115.2C is acceptable.