4

UCC3830-4/-5/-6

CAM (Current Amplifier Inverting Input): The average

load current feedback from ISOUT is applied through a

resistor to this pin. The current loop compensation

network is also connected to this pin (see CAO/ENBL

below).

CAO/ENBL (Current Amplifier Output/Chip Enable):

The current loop compensation network is connected

between this pin and CAM. The voltage on this pin is the

input to the PWM comparator and regulates the output

voltage of the system.

The GATE output is disabled

(held low) unless the voltage on this pin exceeds 1V,

allowing the PWM to force zero duty cycle when

necessary. The PWM forces maximum duty cycle when

the voltage on CAO/ENBL exceeds the oscillator peak

voltage

(3V).

A 3.2V

clamp

circuit

prevents

the

CAO/ENBL voltage from rising excessively past the

oscillator peak voltage for excellent transient response.

The user can force this pin below 0.8V externally with an

open collector, disabling the GATE drive.

COMMAND

(Digital-to-Analog

Converter

Output

Voltage):

This

pin

is

the

output

of

the

5-bit

digital-to-analog converter (DAC) and the noninverting

input of the voltage amplifier. The voltage on this pin sets

the switching regulator output voltage. This voltage

ranges from 1.8V to 3.5V as programmed by the 5-bit

DAC according to Table 1. The GATE output is disabled

when all 1s or illegal codes are presented at the 5 Bit

DAC. The COMMAND source impedance is typically

1.2k

Ω and must therefore drive only high impedance

inputs

if

accuracy

is

to

be

maintained.

Bypass

COMMAND with a 0.01

µF, low ESR, low ESL capacitor

for best circuit noise immunity.

COMP (Voltage Amplifier Output): The system voltage

compensation network is applied between COMP and

VFB.

D0 - D4 (DAC Digital Input Control Codes): These are

the DAC digital input control codes, with D0 representing

the least significant bit (LSB) and D4, the most significant

bit (MSB) as shown in Table 1. A bit is set low by being

connected to GND. A bit is set high by floating it, or

connecting it to a 5V source. Each control pin is pulled

up to approximately 5V by an internal 70

µA current

source.

GATE (PWM Output, MOSFET Driver): This output

provides a 4

Ω totem pole driver. Use a series resistor

between this pin and the gate of the external MOSFET to

prevent excessive overshoot.

GND (Signal Ground): All voltages are measured with

respect to GND. Bypass capacitors on the VCC and

VREF pins should be connected directly to the ground

plane near the GND pin.

IS– (Current Sense Amplifier Inverting Input): This pin

is the inverting input to the current sense amplifier and is

connected to the low side of the average current sense

resistor.

IS+ (Current Sense Amplifier Noninverting Input):

This pin is the noninverting input to the current sense

amplifier and is connected to the high side of the

average current sense resistor.

ISOUT (Current Sense Amplifier Output): This pin is

the output of the current sense amplifier. The voltage on

is the fixed gain of the current sense amplifier, equal to

15, I is the current through the sense resistor, and

resistor.

PGND (Power Ground): This pin provides a dedicated

ground for the output gate driver. The GND and PGND

pins should be connected externally using a short printed

circuit board trace close to the IC. Decouple VIN to

PGND with a low ESR capacitor

 0.10µF.

PWRGOOD

(Undervoltage/Lower

Overvoltage

Output): This pin is an open drain output which is driven

low to reset the microprocessor when VSENSE rises

above or falls below its nominal value by 8.5%. The on

resistance of the open drain switch will be no higher than

470

Ω. The OV and UV comparators’ hysteresis is fixed

at 20mV independent of the COMMAND voltage.

VIN (Positive Supply Voltage): This pin supplies power

to the chip. Connect VIN to a stable voltage source of at

least 10.8V. The GATE and PWRGOOD outputs will be

held low until VCC exceeds the upper undervoltage

lockout threshold. This pin should be bypassed directly

to the GND pin.

VFB (Voltage Amplifier Inverting Input): This input is

connected to COMP through a feedback network and to

the power supply output through a resistor or a divider

network.

VREF (Voltage Reference Output): This pin provides

an accurate 5V reference and is internally short circuit

current limited. VREF powers the D/A converter and also

provides a threshold voltage for the UVLO comparator.

For best reference stability, bypass VREF directly to

GND with a low ESR, low ESL capacitor of at least

0.01

µF.

PIN DESCRIPTIONS