Date: 5/25/04

SP6121 Low Voltage, Synchronous Step Down PWM Controller

© Copyright 2004 Sipex Corporation

3

PIN DESCRIPTION

PIN NO.

PIN NAME DESCRIPTION

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

to GND with a low ESL/ESR ceramic capacitor.

2

GND

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

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.

4

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.

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

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.

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 limit threshold have a positive temperature coefficient to provide first order

7

NDRV

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

low or during a fault.

8

PDRV

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

is high or during a fault.

ELECTRICAL SPECIFICATIONS: Continued

PARAMETER

MIN

TYP

MAX

UNITS CONDITIONS

SOFT START, SHUTDOWN, UVLO: continued

Shutdown Threshold Voltage

0.2

0.3

0.4

V

Measured at COMP Pin

Shutdown Input Pull-up Current

5

µA

COMP = 0.2V, Measured at COMP pin

V

2.69

2.79

2.89

V

V

2.59

2.69

2.79

V

V

-

100

-

mV

GATE DRIVERS

PDRV Rise Time

-

40

110

ns

V

PDRV Fall Time

-

40

110

ns

V

NDRV Rise Time

-

40

110

ns

V

PDRV Fall Time

-

40

110

ns

V

PDRV to NDRV Non-Overlap Time

80

ns

V

NDRV to PDRV Non-Overlap Time

50

ns

V