Datasheet

Vybrid Power Consumption and Options, Rev. 0
18 Freescale Semiconductor
Ballast transistor selection
9.1 Ballast transistor examples
There exist many suitable transistors which can be used as the reference. Two examples were tested and
measured. The first of them was on Semiconductor NJD2873T4 transistor, the default transistor on
TWR-VF65GS10. The second transistor is much smaller. NXP PBSS4021NT is suitable for smaller
currents and power dissipation.
On Semiconductor NJD2873T4 datasheet data (Currently used on TWR-VF65GS10):
• 50V, 2A, NPN
•h
FE
= 120-360/500mA
•U
CE sat
for 500mA 100C: 90mV; for 1000mA 100C: 160mV
• 15W on DPAC
NXP PBSS4021NT datasheet data:
• 20 V, 4.3A, NPN, low VCEsat
•h
FE
= 550/500mA (typical)
•U
CE sat
for 500mA 100C: 28mV; for 1000mA 100C: 50mV
• 390 mW, 660 mW, 1100 mW on SOT23 (depends on PCB)
9.2 Measured data
Both transistors were measured at three different collector currents and three power supply voltages levels.
Table 11. I
C
= 260mA (Linux use case with Video play were used)
Transistor NJD2873T4 PBSS4021NT
V
C
[V] 3.32 1.50 1.35 3.32 1.50 1.35
V
E
[V] 1.21 1.21 1.21 1.21 1.21 1.21
V
B
[V] 1.83 1.91 1.93 1.73 1.85 1.85
I
B
[mA] 1.16 1.28 2.00 0.3 0.36 0.49
Table 12. I
C
= 620mA (additional 3.3 load on 1.2V, external power supply)
Transistor NJD2873T4 PBSS4021NT
V
C
[V] 1.5 1.35 1.5 1.35
I
B
[mA] 4.3 13.8 0.97 1.31
Table 13. I
C
= 810mA (additional 2.2 load on 1.2V, external power supply)
Transistor NJD2873T4 PBSS4021NT