DRV8701

www.ti.com

SLVSCX5B – MARCH 2015 – REVISED JULY 2015

7.4.1 Operating DRV8701 and H-Bridge on Separate Supplies

The DRV8701 can operate with a different supply voltage (VM) than the system H-bridge supply (VBAT). Case 1

describes normal operation when VM and VBAT are roughly the same. Special considerations must be taken into

account for Cases 2, 3, and 4.

•

Case 1: VM

≈ VBAT. Recommended operation

•

Case 2: VM > VBAT. IDRIVE must be shorted to AVDD to disable the high-side OCP. The IDRIVE current is

fixed at 25-mA source and 50-mA sink. This case can allow the driver to better enhance the external FETs for

VBAT < 11.5 V, or operate down to a lower supply voltage below 5.9 V.

•

Case 3: VM > VBAT (higher than Case 2). IDRIVE must be shorted to AVDD to disable the high-side OCP.

This case can also allow the driver to better enhance the external FETs, or operate down to a lower supply

voltage below 5.9 V. The IDRIVE current is fixed at 25-mA source and 50-mA sink. Excess gate drive current

may be driven through the DRV8701 gate clamps causing additional power dissipation in the DRV8701.

•

Case 4: VM < VBAT. The high-side FETs may not be in saturation. There may be a significant voltage drop

across the high-side FET when driving current. This causes high power dissipation in the external FET. When

operating in Case 4, the external FET threshold voltage must be greater than 2 V. Otherwise the DRV8701

will report a pre-driver fault whenever the FET is out of saturation.

Table 9. VM Operational Range based on VBAT

VBAT Range

Case 3

Case 2

Case 1

Case 4

VM

≥ 5.9 V

1 V

≤ VBAT < 5.9 V

N/A

N/A

VM < 0.5 × VBAT + 5.75 V

VM

≥ 0.5 × VBAT + 5.75 V

VM

≥ 5.9 V

5.9 V

≤ VBAT < 6.4 V

VM

≤ 45 V

VM = VBAT

VM > VBAT

VM < VBAT

VM < 0.5 × VBAT + 5.75 V

6.4 V

≤ VBAT < 11.5 V

VM > 0.6 × VBAT + 2.5 V

VM

≥ 5.9 V

VM

≤ VBAT

VM

≤ 0.6 × VBAT + 2.5 V

11.5 V

≤ VBAT < 14 V

VM > VBAT

N/A

VM > VBAT – 4 V

VM

≥ 5.9 V

VM

≤ 45 V

14 V

≤ VBAT ≤ 45 V

VM

≤ VBAT

VM

≤ VBAT – 4 V

Figure 33. VM Operating Range Based on Motor Supply Voltage

When nSLEEP is low, VM may be reduced down to 0 V with up to 45 V present at VBAT. However, nSLEEP

should not be brought high until VM is supplied with a voltage aligning with one of the cases outlined above.

Copyright © 2015, Texas Instruments Incorporated

Submit Documentation Feedback

27

Product Folder Links: DRV8701