TP2150B Datasheet, PDF (11/18 Pages) Tripath Technology Inc. – DUAL HIGH SIDE AND LOW SIDE MOSFET DRIVER

Tripath Technology, Inc. - Technical Information
Application Information
Overcurrent Protection
The TP2150B has over-current protection circuitry to protect itself and the output MOSFETs from
short-circuit conditions. The TP2150B uses the voltage across a resistor R_S (measured via
OCS1HP, OCS1HN, OCS1LP and OCS1LN for channel 1 of the TP2150B) that is in series with
each output MOSFET to detect an over-current condition. R_S and R_OCR are used to set the over-
current threshold. The OCS pins must be Kelvin connected for proper operation.
The TP2150B has overcurrent sense pins for both the high side output MOSFETs and the low side
output MOSFETs. The OCSXHP and OCSXHN pins (pins 33 and 34, pins 50 and 51) sense the
amount of current flowing out of the high side MOSFET. The OCSXLP and OCSXLN pins (pins 30
and 31, pins 53 and 54) sense the amount of current flowing into the low side MOSFET. These
pins sense the voltage across a low resistance value resistor (R_S) and this voltage is gained up
and reflected at OCD1 (pin7) for channel 1. The OCD pins can be used to trigger an overcurrent
condition at the output MOSFETs and then turn off the processor.
Setting Over-current Threshold
R_S and R_OCR determine the value of the over-current threshold, I_SC:
I_SC = 3580 x (V_TOC – I_BIAS * R_OCR)/(R _OCR * R_S)
R_OCR = (3580 x V_TOC)/(I_SC * R_S+3580 * I_BIAS)
where:
R_S and R_OCR are in Ω
V_TOC = Over-current sense threshold voltage for the processor
= 1.0V (typically for the Tripath TC2000 and TC2001)
I_BIAS = 20uA
For example, to set an I_SC of 4.73A, R_OCR = 30.1kΩ and R_S will be 10mΩ.
As high-wattage resistors are usually only available in a few low-resistance values (10mΩ, 25mΩ
and 50mΩ), R_OCR can be used to adjust for a particular over-current threshold using one of these
values for R_S.
It should be noted that the addition of the bulk C_HBR capacitor shown in the Application / Test
Diagram will increase the I_SC level. Thus, it will be larger than the theoretical value shown above.
With C_HBR as shown in the typical application circuit, and with R_OCR = 30.1kΩ and R_S 10mΩ, the
typical current trip point is 7A. Once the designer has settled on a layout and specific C_HBR value,
the system I_SC trip point can be adjusted by increasing the R_OCR value. The R_OCR should be
increased to a level that allows expected range of loads to be driven well into clipping without
current limiting while still protecting the output MOSFETs in case of a short circuit condition.
VN10 Supply and Switch Mode Power Supply Controller
VN10 is an additional supply voltage required by the TP2150B. VN10 must be 10 volts more
positive than the nominal VNN. VN10 must track VNN. Generating the VN10 supply requires
some care.
The proper way to generate the voltage for VN10 is to use a 10V-postive supply voltage
referenced to the VNN supply. The TP2150B has an internal switch mode power supply controller
which generates the necessary floating power supply for the MOSFET driver stage in the
TP2150B (nominally 10V with the external components shown in Application / Test Circuit). The
SMPSO pin (pin 60) provides a switching output waveform to drive the gate of a P channel
MOSFET. The source of the P channel MOSFET should be tied to power ground and the drain of
the MOSFET should be tied to the VN10 through a 100uH inductor. Tripath recommends using
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TP2150B - MC/ 1.7/06.04