NXP Semiconductors
TEA1993TS
GreenChip synchronous rectifier controller
TEA1993TS All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2016. All rights reserved.
Product data sheet Rev. 1.1 — 14 September 2016
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8.4 Synchronous rectification (DRAIN and SOURCE pins)
The IC senses the voltage difference between the drain sense (DRAIN pin) and the
source sense (SOURCE pin) connections. This drain source differential voltage of the SR
MOSFET is used to drive the gate of the SR MOSFET.
In the regulation phase, the IC regulates the difference between the drain and the source
sense inputs to an absolute level of 37 mV. When the absolute difference exceeds 37 mV
(V
reg(drv)
), the gate driver output increases the gate voltage of the external SR MOSFET
until the 37 mV level is reached. The SR MOSFET does not switch off at low current. To
avoid that the device switches off because of ringing, a minimum on-time of 1.5 μs (t
tact(sr)
(min)
) is integrated.
When the absolute difference is < 30 mV, the gate driver output decreases the gate
voltage of the external SR MOSFET. The voltage waveform on the SR MOSFET gate
follows the waveform of the current through the SR MOSFET. When the current through
the SR MOSFET reaches zero, the SR MOSFET is quickly switched off.
After SR MOSFET switch-off, the drain voltage increases. When the drain voltage
exceeds 300 mV, a low ohmic gate pull-down of 7 Ω keeps the gate of the SR MOSFET
switched off.
8.5 Gate driver (GATE pin)
The gate driver circuit charges the gate of the external SR MOSFET during the rising part
of the current. The driver circuit discharges the gate during the falling part of the current.
The gate driver has a source capability of typically 0.50 A and a sink capability of typically
0.65 A, allowing fast turn-on and fast turn-off of the external SR MOSFET.
The maximum output voltage of the driver is limited to 12 V. This high output voltage
drives all MOSFET brands to the minimum on-state resistance. In applications where the
IC is supplied with 5 V, the maximum output voltage of the driver is 4.2 V and logic level
SR MOSFETs can be used (see Figure 3).
The IC is self-supplying in applications with high-side rectification or in battery charging
applications with an output voltage below 4.7 V. When the XV pin is connected to ground
for driving standard SR MOSFETs, the driver is regulated to 9 V. When the XV pin is
connected to the converter output for driving logic-level SR MOSFETs, the driver is
regulated to 4 V if the output voltage is below 4.7 V.
