Texas Instruments UC3914N, UC3914DWTR, UC3914DW, UC2914DWTR, UC2914J Datasheet

UC1914
UC2914
UC3914

SLUS425A - AUGUST 1999

FEATURES

•

5V to 35V Operation

•

Precision Maximum Current Control

•

Precision Fault Threshold

•

Programmable Average Power
Limiting

•

Programmable Overcurrent Limit

•

Shutdown Control

•

Charge Pump for Low R

DS(on)

High-Side Drive

•

Latch Reset Function Available

•

Output Drive V

GS

Clamping

•

Fault Output Indication

• 18 Pin DIL and SOIC Packages

5V to 35V Hot Swap Power Manager

BLOCK DIAGRAM

UDG-95134-2

DESCRIPTION

The UC3914 family of Hot Swap Power Managers provides complete
power management, hot swap and fault handling capability. Integrating this
part and a few external components, allows a board to be swapped in or
out upon failure or system modification without removing power to the hard

-

ware, while maintaining the integrity of the powered system. Complemen

­tary output drivers and diodes have been integrated for use with external
capacitors as a charge pump to ensure sufficient gate drive to the external
NMOS transistor for low R

DS(on)

. All control and housekeeping functions
are integrated and externally programmable and include the fault current
level, maximum output sourcing current, maximum fault time and average
power limiting of the external FET. The UC3914 features a duty ratio cur

­rent limiting technique, which provides peak load capability while limiting
the average power dissipation of the external pass transistor during fault
conditions. The fault level is fixed at 50mV with respect to VCC to minimize
total dropout. The fault current level is set with an external current sense re

­sistor. The maximum allowable sourcing current is programmed by using a
resistor divider from VCC to REF to set the voltage on IMAX. The maximum
current level, when the output appears as a current source is
(VCC – V

IMAX

)/R

SENSE

.

(continued)

2

UC1914
UC2914
UC3914

CONNECTION DIAGRAM

ELECTRICAL CHARACTERISTICS:

Unless otherwise specified, TA= 0°C to 70°C for the UC3914, –40°C to 85°C for

the UC2914, and –55°C to 125°C for the UC1914. VCC = 12V, V

PUMP=VPUMP

(max), SD = 5V, CP1 = CP2 = C

PUMP

= 0.01µF.

T

A=TJ

.

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

VCC Section

I

CC

(Note 2) 8 15 mA

VCC = 35V, (Note 2) 12 20 mA

Shutdown I

CC

SD = 0V 500 900 µA

UVLO Turn on threshold 4.0 4.4 V

UVLO Hysteresis 100 200 350 mV

Fault Timing Section

Overcurrent Threshold T

J

= 25°C, with respect to VCC –55 –50 –45 mV

Over operating temperature, with respect to VCC –57 –50 –42 mV

IMAX Input Bias 13µA
CT Charge Current CT = 1V –140 –100 –60 µA
CT Discharge Current CT = 1V 2.0 3.0 4.5 µA

CT Charge Current CT = 1V, Overload condition –6.0 –3.0 –1.5 mA

CT Fault Threshold 2.25 2.50 2.75 V

CT Reset Threshold 0.45 0.50 0.55 V

Output Duty Cycle Fault condition, I

PL

= 0 1.5 3.0 4.5 %

Input Supply Voltage, VCC . . . . . . . . . . . . . . . . . . . . . . . . . 40V

Maximum Forced Voltage

SD

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12V

IMAX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VCC

LR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12V

Maximum Current

FAULT

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA

PLIM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA

Maximum Voltage, FAULT

. . . . . . . . . . . . . . . . . . . . . . . . . 40V

Reference Output Current . . . . . . . . . . . . . . . Internally Limited

Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C

Junction Temperature. . . . . . . . . . . . . . . . . . . –55°C to +150°C

Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C

Unless otherwise indicated, voltages are referenced to ground.
Currents are positive into, negative out of specified terminal.
Consult Packaging Section of Databook for thermal limitations
and considerations of package.

ABSOLUTE MAXIMUM RATINGS

When the output current is less than the fault level, the
external output transistor remains switched on. When the
output current exceeds the fault level, but is less than the
maximum sourcing level programmed by IMAX, the out­put remains switched on, and the fault timer starts to
charge C

T

, a timing capacitor. Once CTcharges to 2.5V,

the output device is turned off and C

T

is slowly dis-

charged. Once C

T

is discharged to 0.5V, the IC performs
a retry and the output transistor is switched on again.
The UC3914 offers two distinct reset modes. In one

mode with LR left floating or held low, the IC will repeat­edly try to reset itself if a fault occurs as described
above. In the second mode with LR held high, once a
fault occurs, the output is latched off until either LR is
toggled low, the part is shutdown then re-enabled using
SD,

or the power to the part is turned off and then on

again.

This part is offered in both 18 pin DW Wide-Body (SOIC)
and Dual-In-Line (DIL) packages.

DESCRIPTION (cont.)

DIL-18, SOIC-18 (Top View)
N or J Package, DW Package

3

UC1914
UC2914
UC3914

ELECTRICAL CHARACTERISTICS:

Unless otherwise specified, TA= 0°C to 70°C for the UC3914, –40°C to 85°C for the

UC2914, and –55°C to 125°C for the UC1914. VCC = 12V, V

PUMP=VPUMP

(max), SD = 5V, CP1 = CP2 = C

PUMP

= 0.01µF.

T

A=TJ

.

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

Output Section

OUT High Voltage VOUTS = VCC, VPUMP = VPUMP max, with respect to

VPUMP

–1.5 –1.0 V

OUT High Voltage VOUTS = VCC, VPUMP = VPUMP max, IOUT = –2mA,

with respect to VPUMP

–2.0 –1.5 V

OUT Low Voltage I

OUT

= 0 0.8 1.3 V

I

OUT

= 5mA 1 2 V

I

OUT

= 25mA, Overload Condition, VOUTS = 0V 1.2 1.8 V

OUT Clamp Voltage VOUTS = 0V 11.5 13.0 14.5 V

Rise Time C

OUT

= 1nF (Note 1) 750 1250 ns

Fall Time C

OUT

= 1nF (Note 1) 250 500 ns

Charge Pump Section

OSC, OSCB Frequency 60 150 250 kHz

OSC, OSCB Output High I

OSC

= –5mA 10.0 11.0 11.6 V

OSC, OSCB Output Low I

OSC

= 5mA 0.2 0.5 V

OSC, OSCB Output Clamp Voltage VCC = 25 18.5 20.5 22.5 V

OSC, OSCB Output Current Limit High Side Only –20 –10 –3 mA

Pump Diode Voltage Drop I

DIODE

= 10mA, Measured from PMP to PMPB, PMPB to

VPUMP

0.5 0.9 1.3 V

PMP Clamp Voltage VCC = 25 18.5 20.5 22.5 V

VPUMP Maximum Voltage VCC = 12, VOUTS = VCC, Voltage Where Charge Pump

Disabled

20 22 24 V

VCC = 35V, VOUTS = VCC, Voltage Where Charge
Pump Disabled

42 45 48 V

VPUMP Hysteresis VCC = 12, VOUTS = VCC, Voltage Where Charge Pump

Re-enabled

0.3 0.7 1.4 V

VCC = 35V, VOUTS = VCC, Charge Pump Re-enabled 0.25 0.7 1.4 V

Linear Current Section

Input Offset Voltage –15 0 15 mV

Voltage Gain 60 80 dB

IMAX Control Voltage IMAX = OUT, SENSE = VCC, with respect to VCC –20 0 20 mV

IMAX = OUT, SENSE = REF, with respect to REF –20 0 20 mV

SENSE Input Bias 1.5 3.5 µA

Reference Section

REF Output Voltage With respect to VCC –2.25 –2.00 –1.75 V

REF Current Limit 12.5 20.0 50.0 mA

Load Regulation I

VREF

= 1mA to 5mA 25 60 mV

Line Regulation VCC = 5V to 35V 25 100 mV

Shutdown Section

Shutdown Threshold 0.6 1.5 2.0 V

Input Current SD

= 5V 150 300 µA

Delay to Output (Note 1) 0.5 2.0 µs

Fault Section

Fault Output Low I

FAULT

= 1mA 100 200 mV

Fault Output Leakage V

FAULT

= 35V 10 500 nA

4

UC1914
UC2914
UC3914

PIN DESCRIPTIONS

CT: A capacitor is connected to this pin in order to set

the maximum fault time. The minimum fault time must be
more than the time to charge external load capacitance.
The fault time is defined as:

T

CT

I

FAULT

CH

=

•2

where I

CH

= 100µA+IPL, where IPLis the current into the

power limit pin. Once the fault time is reached the output
will shutdown for a time given by:

T

CT

I

SD

DIS

=

•2

where I

DIS

is nominally 3µA.

FAULT:

Open collector output which pulls low upon any
of the following conditions: Timer fault, Shutdown, UVLO.
This pin MUST be pulled up to VCC or another supply
through a suitable impedance.

GND: Ground reference for the IC.

IMAX: This pin programs the maximum allowable

sourcing current. Since REF is a –2V reference (with re

­spect to VCC), a voltage divider can be derived from
VCC to REF in order to generate the program level for
the IMAX pin. The current level at which the output ap

­pears as a current source is equal to the voltage on the
IMAX pin, with respect to VCC, divided by the current
sense resistor. If desired, a controlled current startup can
be programmed with a capacitor on IMAX to VCC.

LR: If this pin is held high and a fault occurs, the timer
will be prevented from resetting the fault latch when CT is
discharged below the reset comparator threshold. The
part will not retry until this pin is brought to a logic low or

a power-on-reset occurs. Pulling this pin low before the
reset time is reached will not clear the fault until the reset
time is reached. Floating or holding this pin low will result
in the part repeatedly trying to reset itself if a fault oc­curs.

OUT: Output drive to the MOSFET pass element. Inter­nal clamping ensures that the maximum V

GS drive is

15V.

OSC, OSCB: Complementary output drivers for interme­diate charge pump stages. A 0.01µF capacitor should be
placed between OSC and PMP, and OSCB and PMPB.

PLIM: This feature ensures that the average MOSFET
power dissipation is controlled. A resistor is connected
from this pin to VCC. Current will flow into PLIM which
adds to the fault timer charge current, reducing the duty
cycle from the typical 3% level. When I

PL >> 100µA then

the average MOSFET power dissipation is given by:
P

FET_AVG = IMAX • 3 • 10

–6

•RPL.

PMP, PMPB: Complementary pins which couple charge
pump capacitors to internal diodes and are used to pro

-

vide charge to the reservoir capacitor tied to VPUMP.
Typical capacitor values used are 0.01µF.

REF: –2V reference with respect to VCC used to pro

-

gram the IMAX pin voltage. A 0.1µF ceramic or tantalum
capacitor MUST be tied between this pin and VCC to en

-

sure proper operation of the chip.

SD:

When this TTL compatible input is brought to a logic
low, the output of the linear amplifier is driven low,
FAULT

is pulled low and the IC is put into a low power
mode. The ABSOLUTE maximum voltage that can be
placed on this pin is 12V.

ELECTRICAL CHARACTERISTICS: Unless otherwise specified, T

A

= 0°C to 70°C for the UC3914, –40°C to 85°C for the

UC2914, and –55°C to 125°C for the UC1914. VCC = 12V, V

PUMP=VPUMP

(max), SD = 5V, CP1 = CP2 = C

PUMP

= 0.01µF.

T

A=TJ

.

PARAMETER TEST CONDITIONS MIN TYP MAX UNITS

Latch Section

LR Threshold High to Low 0.6 1.4 2.0 V
Input Current LR = 5V 500 750 µA

Power Limiting Section

Duty Cycle Control In Fault, I

PLIM

= 200µA 0.6 1.3 2.0 %

In Fault, I

PLIM

= 3mA 0.05 0.12 0.20 %

Overload Section

Delay to Output (Note 1) 500 1250 ns

Threshold Respect to IMAX –250 –200 –150 mV

Note 1: Guaranteed by design. Not 100% tested in production.
Note 2: A mathematical averaging is used to determine this value. See Application Section for more information.

5

UC1914
UC2914
UC3914

SENSE: Input voltage from current sense resistor. When

there is greater than 50mV across this pin with respect to
VCC, a fault is sensed and C

T

begins to charge.

VCC: Input voltage to the IC. Typical voltages are 4.5V to
35V. The minimum input voltage required for operation is

4.5V.

VOUTS: Source connection of external N-channel MOS

-

FET and sensed output voltage of load.

VPUMP: Charge pump output voltage. A capacitor
should be tied between this pin and VOUTS with a typi

-

cal value being 0.01µF.

PIN DESCRIPTIONS (cont.)

0

0.5

1

1.5

2

2.5

3

3.5

-55 -40 0 25 70 85 125
TEMPERATURE (°C)

V

IO

(mV)

Linear Amp VIOvs. Temperature

-52

-51.5

-51

-50.5

-50

-49.5

-49

-48.5

-48

-55 -40 0 25 70 85 125
TEMPERATURE (°C)

FAULT THRESHOLD (mV)

Fault Threshold vs. Temperature

CT I

CHARGE

vs. Temperature VCC - REF vs Temperature

I

MAX

& SENSE Input Bias vs. Temperature

CT I

DISCHARGE

vs. Temperature

Figure 1. Typical characteristic curves.

TYPICAL CHARACTERISTIC CURVES