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Gate Drive Pin (GD) and Isolation Switch Selection

Vin

6 V

I (GD)

Switch

R (GD)

High Voltage Stress Test (HVS)

HVS

FB1

R1 + R2||R 3

R1 + R2||R3

= V

= 1.24V

R2||R3

(7)

H VS

HV S

R3 =

1.24V

(8)

Overvoltage Protection

TPS65166

SLVS976 – SEPTEMBER 2009.......................................................................................................................................................................................... www.ti.com

The external isolation switch disconnects the boost converter once the device is turned off. If the boost converter

is enabled by EN2 and the delay time set by DLY1 passed by, the gate pin GD is pulled low by an internal 10

µA

current sink to minimize inrush current until the Gate-Source voltage is clamped at about VIN -6 V. An internal 10

Ω pull up resistor to VIN is connected to GD to open the isolation switch if the Gate Drive is disabled. Using a

gate drain capacitor of typically 1 nF allows to increase the turn on time of the MOSFET for further inrush current

minimization. If the boost feedback voltage falls below 100mV for more than 1.4 ms, GD is pulled high and the

boost converter shuts down. The device does not recover automatically from shut down but Enable or

unvervoltage lockout must be toggled. Using this configuration allows to optimize the solution to specific

application requirement and different MOSFETs can be used. A standard P-Channel MOSFET with a current

rating close to the maximal used switch current of the boost converter is sufficient. The worst case power

dissipation of the isolation switch is the maximal used switch current x RDS(on) of the MOSFET. A standard

SOT23 package or similar is able to provide sufficient power dissipation.

Table 1. Isolation Switch Selection

COMPONENT SUPPLIER

CURRENT RATING

Vishay Siliconix Si3443CDV

4.7 A / 60 m

Ω

Vishay Siliconix Si3433DS

6 A / 38 m

Ω

International Rectifier IRLML6402

3.7 A / 65 m

Ω

Figure 25. GD Drive

The device has a high voltage stress test. This allows programming the boost converter output voltage VS higher

by the resistor connected to RHVS once HVS is pulled high. With HVS = high the RHVS pin is switched to GND.

The resistors R2 and R3 are connected parallel and therefore the overall resistance is reduced. This changes the

output voltage during the High Voltage Stress Test to a higher value:

With:

VsHVS = Boost converter output voltage with HVS high

The boost converter has two overvoltage protection mechanisms for the switch. Vs is monitored with an

overvoltage protection comparator on the OS pin and as soon as 19.5V typical is reached, the boost converter

stops switching. The converter also detects overvoltage if the feedback voltage at the feedback pin FB1 is 3%

above the typical regulation voltage of 1.24V, which stops switching. The converter starts switching again if the

output voltage falls below the overvoltage thresholds.

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