TD62708 查看數據表（PDF） - Toshiba

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TD62708

8CH HIGH CURRENT SOURCE DRIVER

Toshiba 

TD62708N

Thermal calculation

Where, power dissipation = (VCC1 × ICC1) + (VCC2 × ICC2 × ch × Duty) + (VOH × IOH × ch × Duty)

and the transient thermal resistance of DIP24N (R + h) = 70°C / W, the junction temperature (Tj) is :

Tj (MAX) ≥ (PD × R + h) + Ta (MAX) ··············· expression (A)

Conditions:VCC1 = 5 V (ICC1 = approx. 8 mA), VCC2 = 30 V (ICC2 = approx. 5 mA), 1ch on

VOH = approx. 2.0 V, IOH = 1.44 A,

Tj (MAX) = 120°C, ambient temperature (MAX) : Ta = 70°C

(1) When VCC2 and VC are connected:

Due to expression (a), for designs without cooling fins, duty = approx. 20% is required, as the following

calculation shows :

PD = (5 V × 8 mA) + (30 V × 5 mA × 1ch × 0.2) + (2.0 V × 1.44 A × 1ch × 0.2)

= 40 mW + 30 mW + 576 mW

= 646 mW

Tj (MAX) ≥ (646 mW × 70°C / W) + 70°C = approx. 115°C ··············· OK

(2) When an external resistor (REXT = 0.9 Ω) is connected between VCC2 and VC :

Change the above condition :

VOH = 2.0 V − (0.9 Ω × 1.44 A)

= 0.7 V

PD when substituted in expression (a) :

PD = (5 V × 8 mA) + (30 V × 5 mA × 1 × 0.2) + (0.7 V × 1.44 A × 1 × 0.2)

= 40 mW + 30 mW + 202 mW

= 272 mW

Tj (MAX) ≥ (272 mW × 70°C / W) + 70°C = approx. 89°C

when Tj (MAX) = 120°C

·

·

·

(calculation omitted)

Duty can be approx. 58%.

6

2003-06-04

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