TFS7705H datasheet(5/42 Pages) POWERINT

5 / 42 page

Rev. B 04/15

TFS7701-7708

www.power.com

Pin Functional Description

MAIN DRAIN (D) Pin

Drain of the low-side MOSFET transistor forward converter.

STANDBY DRAIN (DSB) Pin

Drain of the MOSFET of standby power supply.

GROUND (G) Pin

This pin gives a signal current path to the substrate of the

low-side controller. This pin is provided to allow a separate

Kelvin connection to the substrate of the low-side controller to

eliminate inductive voltages that might be developed by high

switching currents in the SOURCE pin. The GROUND pin is

not intended to carry high currents, it is intended as a voltage-

reference connection only.

SOURCE (S) Pin

SOURCE pin that is common to both the standby and main

supplies.

RESET (R) Pin

This pin provides information to limit the maximum duty cycle as a

function of the current fed into the LINE-SENSE and RESET pins

to prevent cycle-by-cycle saturation of main transformer. This pin

can also be pulled up to bypass to signal remote-on/off of the

main converter only.

ENABLE (EN) Pin

This is the ENABLE and CURRENT LIMIT SELECTION pin for

the standby controller. Prior to start-up the resistor value

connected from ENABLE to BYPASS, is detected to select one

of several internal standby current limit values.

LINE-SENSE (L) Pin

This pin provides input bulk voltage line-sense function. This

information is used by the undervoltage and overvoltage

detection circuits for both main and standby. The pin can also

be pulled up to BYPASS or be pulled down to SOURCE to

implement a remote-on/off of both standby and main supplies

simultaneously. The LINE-SENSE pin works in conjunction with

the RESET pin to implement a duty cycle limit function. The

LINE-SENSE pin compensates the value of standby current

limit so as to flatten the output overload power characteristic as

a function of input voltage.

FEEDBACK (FB) Pin

This pin provides feedback for the main two transistor forward

converter. An increase in sink current from the FEEDBACK pin to

ground, reduces the operating duty cycle. This pin also selects

the main device current limit at start-up (in a similar manner to

ENABLE pin).

BYPASS (BP) Pin

This is the decoupled operating voltage pin for the low-side

controller. At start-up the capacitor connected to this pin is

charged from an internal current source. During normal operation

the capacitor voltage is maintained by drawing current from the

low-side bias winding on the standby power supply. This pin is

also used to implement remote-on/off for the main controller.

This is done by driving extra current into the BYPASS pin when

we want to turn-on the main controller. The BYPASS pin also

implements a latch-off function to disable standby and main

when the BYPASS pin current exceeds a threshold. The latch is

reset when LINE-SENSE pin falls below UV (off) standby

threshold. The BYPASS pin capacitor value selects for either

66 kHz (1

mF) or 132 kHz (10 mF) main switching frequency.

HIGH-SIDE OPERATING VOLTAGE (VDDH) Pin

This is the high-side bias (VDD) of approximately 11.5 V. This

voltage is maintained with current from an internal high-voltage

current source and/or from a bootstrap diode from the low-side

standby bias supply.

HIGH-SIDE SOURCE (HS) Pin

SOURCE pin of the high-side MOSFET.

HIGH-SIDE DRAIN (HD) Pin

DRAIN pin of the high-side MOSFET. This MOSFET is floating

with respect to low-side source and ground.

Figure 2.

Pin Configuration.

PI-6774-030713

10 11

5 6 7 8

H Package (eSIP-16F)

Exposed Pad

(Backside) Internally

Connected to SOURCE

Pin (see eSIP-16F

Package Drawing)

Exposed Metal

(On Edge)

Internally

Connected

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