SP6137HV Datasheet, PDF(5/13 Page) Sipex Corporation – Dual Supply Synchronous Buck Controller

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SP6137HV Datasheet, PDF (5/13 Pages) Sipex Corporation – Dual Supply Synchronous Buck Controller

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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 SP6137HV is forced into an idle state

where the output drivers are held off for a finite

period before a re-start is attempted.

Under Voltage Lock Out (UVLO)

The SP6137HV 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 SP6137HV is per-

mitted to start up pending the removal of all

other faults. Both the VCC and VIN UVLO com-

parators have been designed with hysteresis to

prevent noise from resetting a fault.

Soft Start

âSoft Startâ 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 * DVOUT / DTSoft-start

The SP6137HV provides the user with the op-

tion 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 * DVOUT *10ÂµA / (CSS * 0.8V)

THEORY OF OPERATION: Continued

Hiccup

Upon the detection of a power, thermal, or short-

circuit fault, the SP6137HV is forced into an

idle state for 100mS (typical). The SS and COMP

pins are immediately pulled low, and the gate

drivers are held off for the duration of the

timeout period. Power and thermal faults have

to be removed before a restart may be attempted,

whereas, a short-circuit fault is internally cleared

shortly after the fault latch is set. Therefore, a

restart attempt is guaranteed every 100mS (typi-

cal) as long as the short-circuit condition per-

sists.

Thermal and Short-Circuit

Protection

Because the SP6137HV is designed to drive

large NFETs running at high current, there is a

chance that either the controller or power con-

verter will become too hot. Therefore, an inter-

nal thermal shutdown (145Â°C) has been in-

cluded to prevent the IC from malfunctioning at

extreme temperatures.

A short-circuit detection comparator has also

been included in the SP6137HV to protect against

the accidental short or sever 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

SP6137HV is capable of detecting short-circuit

faults throughout the duration of soft start as

well as in regular operation.

Error Amplifier and Voltage Loop

As stated before, the heart of the SP6137HV

voltage error loop is a high performance, wide

bandwidth transconductance amplifier. Because

of the amplifierâs current limited (+/-150ÂµA)

transconductance, there are many ways to com-

pensate the voltage loop or to control the COMP

pin externally. If a simple, single pole, single

Date: 5/25/04

SP6137HV Dual Supply, Synchronous Buck Controller

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