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

UC1914 UC2914 UC3914

5V to 35V Hot Swap Power Manager

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 RDS(on) High-Side Drive

•Latch Reset Function Available

•Output Drive VGS Clamping

•Fault Output Indication

•18 Pin DIL and SOIC Packages

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 hardware, while maintaining the integrity of the powered system. Complementary 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 RDS(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 current 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 resistor. 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 – VIMAX)/RSENSE.

(continued)

BLOCK DIAGRAM

UDG-95134-2

SLUS425A - AUGUST 1999

ABSOLUTE MAXIMUM RATINGS

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.

UC1914

UC2914

UC3914

CONNECTION DIAGRAM

DIL-18, SOIC-18 (Top View)

N or J Package, DW Package

DESCRIPTION (cont.)

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 CT, a timing capacitor. Once CT charges to 2.5V, the output device is turned off and CT is slowly discharged. Once CT 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.

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, VPUMP = VPUMP(max), SD = 5V, CP1 = CP2 = CPUMP = 0.01 F. TA = TJ.

PARAMETER			TEST CONDITIONS	MIN	TYP	MAX	UNITS
VCC Section
ICC		(Note 2)			8	15	mA
		VCC = 35V, (Note 2)			12	20	mA
							A
Shutdown ICC		SD = 0V			500	900
UVLO		Turn on threshold			4.0	4.4	V
UVLO Hysteresis				100	200	350	mV
Fault Timing Section
Overcurrent Threshold		TJ = 25°C, with respect to VCC		–55	–50	–45	mV
		Over operating temperature, with respect to VCC		–57	–50	–42	mV
IMAX Input Bias					1	3	A
CT Charge Current		CT = 1V		–140	–100	–60	A
CT Discharge Current		CT = 1V		2.0	3.0	4.5	A
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, IPL = 0		1.5	3.0	4.5	%

2

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, VPUMP = VPUMP(max), SD = 5V, CP1 = CP2 = CPUMP = 0.01 F. TA = TJ.

PARAMETER			TEST CONDITIONS	MIN	TYP	MAX	UNITS
Output Section
OUT High Voltage		VOUTS = VCC, VPUMP = VPUMP max, with respect to		–1.5	–1.0		V
		VPUMP
OUT High Voltage		VOUTS = VCC, VPUMP = VPUMP max, IOUT = –2mA,		–2.0	–1.5		V
		with respect to VPUMP
OUT Low Voltage		IOUT = 0			0.8	1.3	V
		IOUT = 5mA			1	2	V
		IOUT = 25mA, Overload Condition, VOUTS = 0V			1.2	1.8	V
OUT Clamp Voltage		VOUTS = 0V		11.5	13.0	14.5	V
Rise Time		COUT = 1nF (Note 1)			750	1250	ns
Fall Time		COUT = 1nF (Note 1)			250	500	ns
Charge Pump Section
OSC, OSCB Frequency				60	150	250	kHz
OSC, OSCB Output High		IOSC = –5mA		10.0	11.0	11.6	V
OSC, OSCB Output Low		IOSC = 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		IDIODE = 10mA, Measured from PMP to PMPB, PMPB to		0.5	0.9	1.3	V
		VPUMP
PMP Clamp Voltage		VCC = 25		18.5	20.5	22.5	V
VPUMP Maximum Voltage		VCC = 12, VOUTS = VCC, Voltage Where Charge Pump		20	22	24	V
		Disabled
		VCC = 35V, VOUTS = VCC, Voltage Where Charge		42	45	48	V
		Pump Disabled
VPUMP Hysteresis		VCC = 12, VOUTS = VCC, Voltage Where Charge Pump		0.3	0.7	1.4	V
		Re-enabled
		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	A
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		IVREF = 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
							A
Input Current		SD = 5V			150	300
Delay to Output		(Note 1)			0.5	2.0	s
Fault Section
Fault Output Low		IFAULT = 1mA			100	200	mV
Fault Output Leakage		VFAULT = 35V			10	500	nA

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, VPUMP = VPUMP(max), SD = 5V, CP1 = CP2 = CPUMP = 0.01 F. TA = 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	A
Power Limiting Section
Duty Cycle Control	In Fault, IPLIM = 200 A	0.6	1.3	2.0	%
	In Fault, IPLIM = 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.

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:

TFAULT = 2 • CT

ICH

where ICH = 100 A + IPL, where IPL is the current into the power limit pin. Once the fault time is reached the output will shutdown for a time given by:

TSD = 2 • CT

IDIS

where IDIS is nominally 3 A.

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 respect 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 appears 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 VGS drive is 15V.

OSC, OSCB: Complementary output drivers for intermediate charge pump stages. A 0.01 F 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 IPL >> 100 A then

the average MOSFET power dissipation is given by: PFET_AVG = IMAX • 3 • 10–6 •RPL.

PMP, PMPB: Complementary pins which couple charge pump capacitors to internal diodes and are used to provide charge to the reservoir capacitor tied to VPUMP. Typical capacitor values used are 0.01 F.

REF: –2V reference with respect to VCC used to program the IMAX pin voltage. A 0.1 F ceramic or tantalum capacitor MUST be tied between this pin and VCC to ensure 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.

4

UC1914

UC2914

UC3914

PIN DESCRIPTIONS (cont.)

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 CT 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.

TYPICAL CHARACTERISTIC CURVES

VOUTS: Source connection of external N-channel MOSFET and sensed output voltage of load.

VPUMP: Charge pump output voltage. A capacitor should be tied between this pin and VOUTS with a typical value being 0.01 F.

Linear Amp VIO vs. Temperature

Fault Threshold vs. Temperature

	3.5
	3
IO (mV)	2.5
	2
	1.5
V
	1
	0.5
	0
	-55	-40	0	25	70	85	125
		TEMPERATURE (°C)

(mV)	-48
	-48.5
	-49
THRESHOLD
	-49.5
	-50
	-50.5
	-51
FAULT
	-51.5
	-52
	-55	-40	0	25	70	85	125
		TEMPERATURE (°C)

CT ICHARGE vs. Temperature

VCC - REF vs Temperature

IMAX & SENSE Input Bias vs. Temperature

CT IDISCHARGE vs. Temperature

Figure 1. Typical characteristic curves.

5