4

UC1638

UC2638

UC3638

Note 1: Oscillator triangle amplitude = 2.5 • PV

±AREF.

Note 2: Deadband =

±(REF − DB), referenced to COMP.

Note 3: Offset = AREFIN

− AREF.

AOUT1, BOUT1: AOUT1 and BOUT1 are open collector

output drivers capable of sinking 50mA. These outputs

can be pulled up to 60V maximum. With a few external

components, these outputs can drive the opposite high

side switches in a full bridge arrangement.

AOUT2, BOUT2: AOUT2 and BOUT2 are totem pole

output drivers capable of driving external power MOS-

FETs directly. The peak current ratings are

±500mA. An

integrated zener clamp limits the drive output amplitude

to approximately 14V to prevent MOSFET gate oxide

overstress. These outputs are configured to drive the

opposite low side switches in a full bridge arrangement.

AREF: The voltage on AREF is simply a buffered ver-

sion of the voltage on AREFIN. In single supply applica-

tions, AREF should be bypassed to VEE with a 0.1

µF

ceramic capacitor to provide a stable reference level for

the internal circuitry.

AREFIN: The voltage on AREFIN is generated inter-

nally by a 50% voltage divider tied between VCC and

VEE. As such, it provides the mid supply reference

needed for the oscillator, voltage amplifier, current am-

plifier and current limit comparators when operating in

single supply mode. A buffer amplifier is connected be-

tween AREFIN and AREF. In bipolar supply applications

AREFIN is usually connected to VEE, which disables

the buffer amplifier, and AREF is connected to 0V.

COMP: This is the output of the high slew rate error am-

plifier. The level on COMP modulates the controller duty

cycle via the PWM comparators and the oscillator ramp.

Compensation and DC gain setting resistors are con-

nected between COMP and INV.

CS-: This is the inverting input to the X5 current sense

amplifier. The common mode input range for this pin ex-

tends from VEE

−1V to VCC−4V. A low value resistor in

PIN DESCRIPTIONS

ELECTRICAL CHARACTERISTICS

Unless otherwise specified; VCC = 15V, VEE =–15V, CT = 680pF, RT = 3k,

−55°C to 125°C for the UC1638, −25°C to 85°C for the UC2638,

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNITS

X5 Amplifier

Gain

4.75

5

5.25

V/V

Common Mode Rejection

±5V

50

65

dB

−3dB Bandwidth

300

400

kHz

Slew Rate Rising

.75

1.5

V/

µs

Slew Rate Falling

.75

1.5

V/

µs

Shutdown

Threshold

Ref. to VCC

− 1.9

− 2.25

− 2.5

V

Input Bias Current

−0.5

−10

µA

Current Limit

Threshold Positive

Measured Between CS+ and CS-

400

500

600

mV

Threshold Negative

Measured Between CS+ and CS-

– 600

− 500

– 400

mV

Propagation Delay to Outputs

Overdrive = 200mV

150

250

ns

Deadband Adjust

Maximum Deadband

±5V

Zero Deadband

0

V

Deadband Adjustment Gain

± 0.9

± 1

± 1.2

V/V

Input Bias Current

3

15

µA

AREF Buffer

Gain

AREF / VCC

− VEE

0.49

0.5

0.51

V/V

Offset

(Note 3)

30

100

mV

(continued)