SP6121 datasheet(3/42 Pages) SIPEX

3 / 42 page

Date: 11/29/04

SP6121 Low Voltage, Synchronous Step Down PWM Controller

PIN DESCRIPTION

PIN NO.

PIN NAME DESCRIPTION

1VCC

Positive input supply for the control circuitry and gate drivers. Properly bypass this pin

to GND with a low ESL/ESR ceramic capacitor.

GND

Ground pin. Both power and control circuitry of the IC is referenced to this pin.

3VFB

Feedback Voltage Pin. It is the inverting input of the Error Amplifier and serves as the

output voltage feedback point for the buck converter. The output voltage is sensed and

can be adjusted through an external resistor divider.

COMP

Output of the Error Amplifier. It is internally connected to the non-inverting input of the

PWM comparator. A lead-lag network is typically connected to the COMP pin to

compensate the feedback loop in order to optimize the dynamic performance of the

voltage mode control loop. Sleep mode can be invoked by pulling the COMP pin below

0.2V with an external open-drain or open-collector transistor. Supply current is reduced

to 25µA (typical) in shutdown. An internal 5µA pull-up ensures start-up.

5ISENSE

Current Limit Sense pin. Connect this pin to the switching node at the junction between

the two external power MOSFET transistors. This pin monitors the voltage dropped

across the RDS(ON) of the high side P-channel MOSFET while it is conducting. When

this drop exceeds the sum of the voltage programmed through the ISET pin plus the

internal 160mV threshold, the overcurrent comparator sets the fault latch and termi-

nates the output pulses. The controller stops switching and goes through a hiccup

sequence. This prevents excessive power dissipation in the external power MOSFETs

during an overload condition. An internal delay circuit prevents that very short and mild

overload conditions, that could occur during a load transient, activate the current limit

circuit.

6ISET

Current Limit Threshold pin. An external resistor connected between this pin and the

source of the high side P-channel MOSFET adds to the internal current limit threshold

of 160mV. If a current limit threshold in excess of 160mV is required, the external

programming resistor can properly be chosen based on the internal 30µA pull down

current available on the ISET pin. Both this 30µA current source and the 160mV built-in

current limit threshold have a positive temperature coefficient to provide first order

correction for the temperature coefficient of the external P-channel MOSFET’s RDS(ON).

NDRV

High current driver output for the low side MOSFET switch. It is always low if PDRV is

low or during a fault.

PDRV

High current driver output for the high side MOSFET switch. It is always high if NDRV

is high or during a fault.

ELECTRICAL CHARACTERISTICS

Unless otherwise specified: 0°C < TA < 70°C, 3.0V < VCC < 5.5V, CCOMP = 22nF, CPDRV = CNDRV = 3.3nF, VFB = 1.25V, ISET = ISENSE = VCC, GND=0V

PARAMETER

MIN

TYP

MAX

UNITS CONDITIONS

SOFT START, SHUTDOWN, UVLO: continued

Shutdown Threshold Voltage

0.2

0.3

0.4

Measured at COMP Pin

Shutdown Input Pull-up Current

µA

COMP = 0.2V, Measured at COMP pin

CC Start Threshold

2.69

2.79

2.89

CC Stop Threshold

2.59

2.69

2.79

CC Hysteresis

100

GATE DRIVERS

PDRV Rise Time

110

CC > 4.5V

PDRV Fall Time

110

CC > 4.5V

NDRV Rise Time

110

CC > 4.5V

PDRV Fall Time

110

CC > 4.5V

PDRV to NDRV Non-Overlap Time

CC > 4.5V

NDRV to PDRV Non-Overlap Time

CC > 4.5V

SP6121 Datasheet(PDF) 3 Page - Sipex Corporation

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