SP6132HCUSLASHTR datasheet(5/10 Pages) SIPEX

5 / 10 page

Date:2/14/06

SP6132H High Voltage, Synchronous PWM Controller

tection features include thermal shutdown and

short-circuit detection. In the event that either a

thermal, short-circuit, or UVLO fault is de-

tected, the SP6132H is forced into an idle state

where the output drivers are held off for a finite

period before a re-start is attempted.

Soft Start

“Soft Start” is achieved when a power converter

ramps up the output voltage while controlling

the magnitude of the input supply source cur-

rent. In a modern step down converter, ramping

up the positive terminal of the error amplifier

controls soft start. As a result, excess source

current can be defined as the current required to

charge the output capacitor.

IVIN = COUT * ∆VOUT / ∆TSoft-start

The SP6132H provides the user with the option

to program the soft start rate by tying a capacitor

from the SS pin to GND. The selection of this

capacitor is based on the 10uA pull up current

present at the SS pin and the 0.8V reference

voltage. Therefore, the excess source can be

redefined as:

IVIN = COUT * ∆VOUT *10µA / (CSS * 0.8V)

Under Voltage Lock Out (UVLO)

The SP6132H contains two separate UVLO

comparators to monitor the bias (VCC) and con-

version (VIN) voltages independently. The VCC

UVLO threshold is internally set to 4.25V,

whereas the VIN UVLO threshold is program-

mable through the UVIN pin. When the UVIN

pin is greater than 2.5V, the SP6132H is permit-

ted to start up pending the removal of all other

faults. Both the VCC and VIN UVLO compara-

tors have been designed with hysteresis to pre-

vent noise from resetting a fault.

Thermal and Short-Circuit

Protection

Because the SP6132H is designed to drive large

NFETs running at high current, there is a chance

that either the controller or power converter will

become too hot. Therefore, an internal thermal

shutdown (145

°C) has been included to prevent

the IC from malfunctioning at extreme tempera-

tures.

A short-circuit detection comparator has also

been included in the SP6132H to protect against

the accidental short or severe build up of current

at the output of the power converter. This com-

parator constantly monitors the positive and

negative terminals of the error amplifier, and if

the VFB pin ever falls more than 250mV (typi-

cal) below the positive reference, a short-circuit

fault is set. Because the SS pin overrides the

internal 0.8V reference during soft start, the

SP6132H is capable of detecting short-circuit

faults throughout the duration of soft start as

well as in regular operation.

Handling of Faults:

Upon the detection of power (UVLO), thermal,

or short-circuit faults, the SP6132H is forced

into an idle state where the SS and COMP pins

are pulled low and the gate drivers are held off.

In the event of UVLO fault, the SP6132H re-

mains in this idle state until after the UVLO fault

is removed. Upon the detection of thermal or

short-circuit faults, an internal 200ms (typical)

timer is activated. In the event of a short-circuit

fault, a re-start is attempted immediately after

the 200ms timeout expires. Whereas, when a

thermal fault is detected the 200ms delay con-

tinuously recycles and a re-start cannot be at-

tempted until the thermal fault is removed and

the timer expires.

THEORY OF OPERATION: Continued

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