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LTC2928

2928f

Multichannel Power Supply

Sequencer and Supervisor

The LTC

2928 is a four channel cascadable power

supply sequencer and high accuracy supervisor. Sequenc-

ing thresholds, order and timing are conﬁgured with just a

few external components, negating the need for PC board

layout or software changes during system development.

Multiple LTC2928s may be easily connected to sequence

an unlimited number of power supplies.

Sequence outputs control supply enable pins or

N-channel pass gates. Precision input comparators with

individual outputs monitor power supply voltages to 1.5%

accuracy. Supervisory functions include undervoltage

and overvoltage monitoring and reporting as well as µP

reset generation. RST may be forced high to complement

margin testing.

Application faults, whether internally or externally gener-

ated, can shutdown all controlled supplies. The type and

source of faults are reported for diagnosis. Individual

channel controls are available to independently exercise

enable outputs and supervisory functions.

A high voltage input allows the LTC2928 to be powered

from voltages as high as 16.5V. A buffered reference

output permits single negative power supply sequencing

and monitoring operations.

■

Network/Telecom Infrastructure

■

Sequencing for Multiple I/O and Core Voltages

■

Power Management

■

Easily Conﬁgure Power Management

without Software

■

Controls Up to Four Supplies per Device

■

Cascades for Additional Supplies

■

Staged Supply Sequencing with

Adjustable Time Positions

■

Fault Event Reporting with Diagnostics

■

Selectable System Shutdown on Fault

■

1.5% Undervoltage Monitor Accuracy

■

Overvoltage and/or Fault Indication

■

Conﬁgurable Undervoltage and

Overvoltage Thresholds

■

Charge Pumped Enable Pins Drive N-Channel

MOSFETs

■

Operates from 2.9V to 16.5V

■

5mm × 7mm 38-lead QFN and

36-lead SSOP Packages

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All

other trademarks are the property of their respective owners. Protected by U.S. Patents

including 4843302, 6949965.

RT1

RT2

RT3

RT4

12V

10k

LTC2928

10k 10k 10k 10k

FAULT

SYSTEM

RESET

1.8V

2.5V

1.2V

3.3V

12.1k

23.2k

36.5k

51.1k

95.3k

0.047

F 3300pF

0.1

100

1 F

24.3k

9.53k

1.5k

3.4k

RST

FLT

DONE

2928 TA06

GND MS1 VSEL RTMR PTMR

EN2HV

EN1 EN4 EN3

STMR

OUT

RUN

LTM4600

OUT

RUN

LTC3414

OUT

RUN

LTC1628

OUT

AUSTIN LYNX

AXA010AY93

ALL RESISTORS 1%

Si7894ADP

3.3V

2.5V

1.8V

1.2V

START

SEQUENCE

START

SEQUENCE

DOWN

SEQUENCE UP

COMPLETE

SEQUENCE

DOWN

COMPLETE

DONE

2928 TA07

1V/DIV

Sequencing Up and Down

Summary of content (32 pages)

PAGE 1
LTC2928 Multichannel Power Supply Sequencer and Supervisor DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ U ■ Easily Configure Power Management without Software Controls Up to Four Supplies per Device Cascades for Additional Supplies Staged Supply Sequencing with Adjustable Time Positions Fault Event Reporting with Diagnostics Selectable System Shutdown on Fault 1.
PAGE 2
LTC2928 AXI U RATI GS (Note 1, 2) U W W W ABSOLUTE Supply Voltages HVCC....................................................... –0.3V to 18V VCC......................................................... –0.3V to 6.5V Input Voltages V1, V2, V3, V4........................................ –0.3V to 12V MS1, MS2, RDIS................................... –0.3V to 6.5V SQT1, SQT2, VSEL ................................ –0.3V to 6.5V RT1, RT2, RT3, RT4............................... –0.3V to 6.5V ON, OVA...........
PAGE 3
LTC2928 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V unless otherwise noted.
PAGE 4
LTC2928 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Sequence Time Position Control Inputs: RT1, RT2, RT3, RT4 (see resistor selection Table 3) VRT(LO) Voltage Required to Force Enable Pin Low While Sequencing ● 0.045 • VCC VRT(HI) Voltage Required to Force Enable Pin High Outside of Sequencing ● 0.
PAGE 5
LTC2928 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 1.189 1.189 0.793 0.396 0.119 1.205 1.205 0.806 0.406 0.129 V V V V V 0.15 0.3 V External Voltage Reference Pin: REF VREF Reference Voltage Output 100% Sequence Threshold 67% Sequence Threshold 33% Sequence Threshold 10% Sequence Threshold IREF = 0.
PAGE 6
LTC2928 TYPICAL PERFORMANCE CHARACTERISTICS IHVCC vs HVCC 1 HVCC = GND 85°C 4 Regulated VCC vs Temperature 3.4 IREG = 0 0.95 85°C REGULATED VCC (V) IVCC vs VCC 5 25°C IHVCC (mA) IVCC (mA) 3 –40°C 2 0.9 25°C 0.85 –40°C 1 0 0.8 2.5 3 3.5 4 4.5 VCC (V) 5 5.5 0.75 6 11 13 HVCC (V) 2928 G08 15 3.35 HVCC = 7.2V 3.3 3.4 IREG = 0 HVCC = 16.5V 3.25 HVCC = 12V 3.
PAGE 7
LTC2928 TYPICAL PERFORMANCE CHARACTERISTICS Reference Output Voltage vs Temperature Comparator Under-Voltage Glitch Immunity GLITCH DURATION ( s) 1.196 1.192 1.188 1k GLITCH DURATION ( s) 1k 1.200 VREF (V) Comparator Over-Voltage Glitch Immunity RESET OCCURS ABOVE CURVE 100 COMPARATOR IGNORES GLITCH OV OCCURS ABOVE CURVE 100 COMPARATOR IGNORES GLITCH 1.184 1.180 –50 0 25 50 TEMPERATURE (°C) –25 75 10 100 1 10 COMPARATOR OVERDRIVE (% OF RESET THRESHOLD) 0.1 2928 G05 10 100 0.
PAGE 8
LTC2928 TYPICAL PERFORMANCE CHARACTERISTICS ICAS(UP) vs Temperature (device configured as MASTER) –75 VCAS = GND 85° –57 –45° 1.5 0.5 –45° 0 25 50 TEMPERATURE (°C) 75 0 100 0.5 0 2 2928 G22 2 VOLTAGE OUTPUT LOW (V) 85° 25° –45° 1 20 0 25 0.75 0.25 6 5 10 15 IOL (mA) 20 25 2928 G24 Enable Current Sink Capability vs VCC and VOL VOL = 0.4V 4 1.25 85° 1 25° –45° 0.75 3 VOL = 0.2V 2 0.
PAGE 9
LTC2928 PIN FUNCTIONS CAS: Cascade Input/Output. Connect the cascade pin between a master and one or more slave devices to increase the number of supplies that can be sequenced per time position. See Applications Information for details. Do not add capacitance to the cascade pin. Leave open if unused. CMP1-CMP4: Comparator and/or Fault Status Outputs. The CMP outputs have a weak internal pull-up to VCC and may be pulled above VCC using an external pull-up.
PAGE 10
LTC2928 PIN FUNCTIONS OVA: Over Voltage Adjust Input. After configuring the undervoltage thresholds, bias this input to set the overvoltage threshold for all positive supplies. Leave the pin floating to set an overvoltage threshold approximately 32% above the undervoltage threshold. Tie OVA to VCC to move the overvoltage threshold above 1V. Consult the Applications Information for details on OVA biasing. PTMR: Power Good Timer.
PAGE 11
LTC2928 PIN FUNCTIONS monitored power supply and ground (or REF for negative supplies monitored on V1). See Applications Information for selecting resistors to configure the monitor thresholds. Voltage monitor inputs operate with their respective RT inputs and EN outputs. and one negative adjustable input. Negative supplies are monitored on the V1 input. See Applications Information for configuration table. V1-V4: Voltage Monitor Inputs.
PAGE 12
LTC2928 TIMING DIAGRAMS The LTC2928 monitors four supply thresholds per supply (sequence-up, sequence-down, undervoltage, overvoltage) during a full system cycle. A full cycle comprises a sequence-up phase, monitor phase and sequence-down phase. A sequence timer sets the time delay between supply enables during both the sequence-up and sequencedown phases. The power-good timer is a watchdog for stalled supplies during the sequence-up and sequencedown phases.
PAGE 13
LTC2928 U OPERATIO At the beginning of the sequence-up phase, a current source begins to charge the STMR capacitance. When the sequence timer has expired the CAS pin pulls low. At this time, any enable (EN) scheduled (using the RT inputs) for “time position 1” pulls high, allowing a supply (or supplies) to be turned on. The CAS pin is held low until all monitored inputs in the current time position exceed their selected sequencing-up threshold (25µs minimum).
PAGE 14
LTC2928 U OPERATIO good timer starts with the first enable output pulling low and is cleared when the last supply monitor input crosses its sequence-down threshold. A sequence-down fault pulls FLT and all enable outputs low. Use a single capacitor from PTMR to ground to select the power good time. To disable the power good timer, tie PTMR to ground. supply failed to meet threshold (or other source of fault). Force all supplies down in an un-sequenced manner by pulling FLT low (external fault).
PAGE 15
LTC2928 APPLICATIO S I FOR ATIO U W U U Fault Detection Reset Faults The LTC2928 has sophisticated fault detection circuitry which can detect: Use the MS1 and MS2 configuration pins to select whether or not the system should fault if any monitored input falls below its undervoltage threshold. A reset fault may only occur after the LTC2928 comes out of reset for the first time after sequencing. All enable outputs and FLT are pulled low.
PAGE 16
LTC2928 APPLICATIO S I FOR ATIO U W U U Should multiple channels fault simultaneously, the reported channel is given priority according to the channel number (1,2,3,4). In the event of an external fault, the LTC2928 fault manager reports overvoltage channels to the fault channel outputs (CMP3, CMP4). If no channel is overvoltage, the default report is channel 4 (High, High). As such, in certain applications, a potential reporting ambiguity exists.
PAGE 17
LTC2928 APPLICATIO S I FOR ATIO U U W U process repeats until CAS clocks through time position 8 and DONE pulls low. To sequence down, the ON input is pulled low. Supplies in time position 8 are disabled. After supplies in time position 8 fall below their sequence-down threshold, CAS is released and pulled high. CAS remains high for one STMR period and then pulls low again to disable supplies in time position 7. The process repeats until CAS clocks through time position 1 and DONE pulls high.
PAGE 18
LTC2928 APPLICATIO S I FOR ATIO U U W U Another interesting application combines the usage of both the CAS pin connection and the DONE—ON communications link. Figure 4 shows a two dimensional configuration of four LTC2928s that allows for 16 supplies to be sequenced in up to 16 time positions.
PAGE 19
LTC2928 APPLICATIO S I FOR ATIO U U W U Correcting for IR Drops Discharging Load Capacitance Sense feedback is common in high current applications. Parasitic resistance coupled with high currents causes voltage drops. The sense pin of a power module is designed to help regulate the voltage at a point in the distribution circuitry beyond the voltage drops. The output of the power module is raised until the desired voltage is achieved at the sense point.
PAGE 20
LTC2928 APPLICATIO S I FOR ATIO U U W DC/DC VIN VOUT SHDN U 12V 3.3V N1 3.3V 100 DC/DC VIN VOUT SHDN 2.5V N2 2.5V 100 36.5k 36.5k 52.3k LTC2928 1N4148 D1 C1 V1 EN2 V2 EN3 V3 EN4 V4 10k HVCC 10k MS1 470 F 10k MS2 VCC 1.5k 1 F EN1 3.4k 95.3k 95.3k 52.3k VCC VSEL RT1 GND RT2 RTMR RT3 PTMR RT4 STMR 10k 0.047 F 0.1 F 3300pF SQT2 SQT1 SYSTEM RESET RST OV 97.6k ON 10k FAULT FLT DONE N1, N2: IRL3714S ALL RESISTORS 1% 3.32k 10k 10k 2928 TA04 Figure 10.
PAGE 21
LTC2928 APPLICATIO S I FOR ATIO U U W U Forcing Supplies Off or Disabling Unused Channels Forcing Supplies On Prior to Sequencing The most convenient way to mask an unused channel is to tie its respective RT input to ground. After sequencing begins, any enable output (EN) may be pulled low permanently by driving the respective RT input to ground (asynchronous OFF command). An asynchronously OFF channel cannot be re-enabled until a new sequence-up procedure is started.
PAGE 22
LTC2928 APPLICATIO S I FOR ATIO U W U U VCC RT1 RT2 RT3 RT4 VCC LTC2928 EN1 EN2 EN3 EN4 SUPPLY BANK V4 V3 V2 V1 ON DONE SEQUENCING UP SEQUENCING DOWN 3.3k VCC DONE EN1-4 SEQUENCING UP 2928 F11 Figure 12. Cycle Supply Enables Repeatedly (useful for system burn-in) VCC RT1 RT2 RT3 RT4 LTC2928 V1 V2 V3 V4 VCC VCC 100k 10k ON FLT 1N4148 ON V1-4 SEQUENCING UP SHUTDOWN RESTART FLT 2928 F12 Figure 13.
PAGE 23
LTC2928 APPLICATIO S I FOR ATIO U W VCC RT1 RT2 RT3 RT4 VCC LTC2928 EN1 EN2 EN3 EN4 VCC 3.3k CONTROLLER ON FLT 1N4148 ON FLT EN1-4 SEQUENCING UP SHUTDOWN 2928 F11a Figure 14. Turn-Off Enables Simultaneously (no sequence-down) 5V LTC3704 –5.2V (VMON(TH) = –4.67V) RUN 10k 43.2k LTC2928 V1 11k REF EN1 VCC VSEL VMON(TH) = –VREF (43.2k/11k) 2928 F12a Figure 15.
PAGE 24
LTC2928 APPLICATIO S I FOR ATIO U W U U LTC2928 Design Example The following design example describes a power supply sequencing application using many features of the LTC2928. The example discusses a configuration procedure for the LTC2928 in a system containing a dual-supply DSP and FPGA. The design example schematic is shown in Figure 20. The three main operating phases—sequence-up, supply monitor, and sequence-down are discussed. All resistor, capacitor and configuration settings are reviewed.
PAGE 25
LTC2928 APPLICATIO S I FOR ATIO U W U U g. Undervoltage thresholds The positive supply monitor undervoltage threshold at all of the monitor inputs is 0.5V. Connect a resistive divider from the sensed voltage to ground. Connect the tap point to the respective high impedance monitor input. Specify the required undervoltage threshold (UVTH) and calculate the divider ratio using RnB UVTH( V) = –1 0.5V RnA This application requires –6.5% undervoltage thresholds for all supplies. For the 1.
PAGE 26
LTC2928 APPLICATIO S I FOR ATIO U W U U 2) Sequence-Up Phase Overvoltage Indication Start the sequence-up phase by transitioning the ON input above 1V. At this point, the LTC2928 senses the sequence position resistors on inputs RT1 through RT4. The sequence timer is operating and the CAS pin pulls low at the start of each time position. The CMP outputs are low during sequencing unless a fault has occurred.
PAGE 27
LTC2928 APPLICATIO S I FOR ATIO U U W U tSTMR ON DONE CAS 1 2 3 4 5 6 7 8 EN3 V3 0.67VMON(TH) EN4 V4 0.67VMON(TH) EN1, EN2 V1 V2 0.67VMON(TH) 0.67VMON(TH) VMON(TH) CMP3, CMP4, CMP1 CMP2 tRTMR RST PTMR RTMR 2928 TA02 Figure 18.
PAGE 28
LTC2928 APPLICATIO S I FOR ATIO U W U U tSTMR ON DONE CAS 8 7 6 5 4 3 2 1 EN1, EN2 V1, V2 0.67VMON(TH) EN4 V4 0.67VMON(TH) EN3 V3 0.67VMON(TH) CMP1, CMP2 CMP3, CMP4 RST PTMR 2928 TA03 Figure 19.
PAGE 29
LTC2928 PACKAGE DESCRIPTIO U G Package 36-Lead Plastic SSOP (5.3mm) (Reference LTC DWG # 05-08-1640) 12.50 – 13.10* (.492 – .516) RECOMMENDED SOLDER PAD LAYOUT 1.25 ±0.12 7.8 – 8.2 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 5.3 – 5.7 0.42 ±0.03 7.40 – 8.20 (.291 – .323) 0.65 BSC 5.00 – 5.60** (.197 – .221) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 2.0 (.079) MAX 0° – 8° 0.09 – 0.25 (.0035 – .010) 0.55 – 0.95 (.022 – .037) NOTE: 1.
PAGE 30
LTC2928 UHF Package 38-Lead Plastic QFN (5mm × 7mm) (Reference LTC DWG # 05-08-1701) 3.15 ± 0.10 (2 SIDES) 0.75 ± 0.05 5.00 ± 0.10 (2 SIDES) 0.00 – 0.05 PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 37 38 0.40 ±0.10 PIN 1 TOP MARK (SEE NOTE 6) 1 2 5.15 ± 0.10 (2 SIDES) 7.00 ± 0.10 (2 SIDES) 0.40 ± 0.10 0.200 REF 0.200 REF 0.75 ± 0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC R = 0.115 TYP (UH) QFN 0205 BOTTOM VIEW—EXPOSED PAD 0.70 ± 0.05 5.50 ± 0.05 (2 SIDES) 4.10 ± 0.05 (2 SIDES) 3.15 ± 0.
PAGE 31
LTC2928 TYPICAL APPLICATIO U RP1 10k DC/DC VIN VOUT SHDN VCC 3.3V N4 DC/DC VIN VOUT 3.3V 10k DC/DC VIN VOUT 1.5V 2.5V CORE FPGA I/O SHDN 1.8V N3 CORE SHDN 3.3V R4B 52.3k LTC2928 RT1 3.4k RT2 3.4k RT3 24.3k RT4 15k 1k 1k 1k 1k 0.1 F SYSTEM CONTROLLER EN1 V1 EN2 V2 EN3 V3 EN4 V4 RT1 HVCC RT2 MS1 RT3 MS2 RT4 VSEL CMP1 GND CMP2 RTMR CMP3 PTMR CMP4 STMR VCC REF SQT2 OVA SQT1 RST CAS OV RDIS FLT ON I/O RST SD1 R1B 36.
PAGE 32
LTC2928 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC2920-1 LTC2920-2 Single/Dual Power Supply Margining Controller Symmetric/Asymmetric High and Low Voltage Margining LTC2921/LTC2922 Power Supply Tracker with Input Monitor Monitor up to Five Supplies, Includes Remote Sense Switches LTC2923 Power Supply Tracking Controller Up to 3 Supplies LTC2924 Quad Power Supply Sequencer Cascadable LTC2925 Multiple Power Supply Tracking Controller with Power Good Timeout Controls Three Supplies Wit