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LTC2970/LTC2970-1

29701fc

Dual I

C Power

Supply Monitor and

Margining Controller

The LTC

2970 is a dual power supply monitor and

margining controller with an SMBus compatible I

C bus

interface. A low-drift, on-chip reference and 14-bit ΔΣ A/D

converter allow precise measurements of supply voltages,

load currents or internal die temperature. Fault manage-

ment allows

⎯

T to be asserted for conﬁ gurable over

and under voltage fault conditions. Two voltage buffered,

8-bit IDACs allow highly accurate programming of DC/DC

converter output voltages. The IDACs can be conﬁ gured

to automatically servo the power supplies to the desired

voltages using the ADC. The LTC2970-1 adds a tracking

feature that can be used to turn multiple power supplies

on or off in a controlled manner.

The bus address is set to 1 of 9 possible combinations by

pin strapping the ASEL0 and ASEL1 pins. The LTC2970/

LTC2970-1 are packaged in the 24-lead, 4mm × 5mm

QFN package.

■

Dual Power Supply Voltage Servo

■

Monitoring Supply Voltage and Current

■

Programmable Power Supplies

■

Programmable Reference

■

Less Than ±0.5% Total Unadjusted Error 14-Bit ΔΣ

ADC with On-Chip Reference

■

Dual, 8-Bit IDACs with 1x Voltage Buffers

■

Linear, Voltage Servo Adjusts Supply Voltages by

Ramping IDAC Outputs Up/Down

■

C™ Bus Interface (SMBus Compatible)

■

Extensive, User Conﬁ gurable Fault Monitoring

■

On-Chip Temperature Sensor

■

Available in 24-Lead 4mm × 5mm QFN Package

Dual Power Supply Monitor and Controller (One of Two Channels Shown)

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.

8V TO 15V

OUT

0.1μF

I–

I+

C BUS

SMBUS

COMPATIBLE

LOAD

DC/DC

CONVERTER

SGND

29701 TA01

RUN/SS

1/2 LTC2970

ALERT

SCL

SDA

GPIO_0

REF

12V

GND

ASEL0 ASEL1

GPIO_CFG

IN0_BM

IN0_BP

IN0_AP

OUT0

IN0_AM

()

TEMPERATURE (°C)

–50

ERROR (%)

–0.25

0.25

29701 TA01b

–0.50

–25 0 50

0.50

100

ADC V

= 5V

15 PARTS MOUNTED ON PCB

ADC Total Unadjusted Error

vs Temperature

Summary of content (36 pages)

PAGE 1
LTC2970/LTC2970-1 Dual I2C Power Supply Monitor and Margining Controller DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ The LTC®2970 is a dual power supply monitor and margining controller with an SMBus compatible I2C bus interface. A low-drift, on-chip reference and 14-bit ΔΣ A/D converter allow precise measurements of supply voltages, load currents or internal die temperature. Fault management allows ⎯A⎯L⎯E⎯R⎯T to be asserted for conﬁgurable over and under voltage fault conditions.
PAGE 2
LTC2970/LTC2970-1 U W W W ABSOLUTE AXI U RATI GS PIN CONFIGURATION (Notes 1 and 2) GPIO_CFG ASEL1 ASEL0 REF RGND TOP VIEW 24 23 22 21 20 VIN0_AP 1 19 SDA VIN0_AM 2 18 SCL VIN0_BP 3 17 ALERT 25 VIN0_BM 4 16 GPIO_0 VIN1_AP 5 15 GPIO_1 VIN1_AM 6 14 IOUT0 13 IOUT1 VOUT1 VOUT0 9 10 11 12 12VIN 8 VDD VIN1_BP 7 VIN1_BM Supply Voltages: VDD ......................................................... –0.3V to 6V 12VIN .................................................... –0.
PAGE 3
LTC2970/LTC2970-1 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. V12VIN = 12V, VDD and REF pins ﬂoating unless otherwise indicated, CVDD = 100nF and CREF = 100nF. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 4.24 7.5 mA 3.7 5 mA 4.14 4.
PAGE 4
LTC2970/LTC2970-1 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. V12VIN = 12V, VDD and REF pins ﬂoating unless otherwise indicated, CVDD = 100nF and CREF = 100nF.
PAGE 5
LTC2970/LTC2970-1 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 400 kHz I2C Interface Timing Characteristics fSCL Serial Clock Frequency (Note 6) ● 10 tLOW Serial Clock Low Period (Note 6) ● 1.3 μs tHIGH Serial Clock High Period (Note 6) ● 0.6 μs tBUF Bus Free Time Between Stop and Start (Note 6) ● 1.
PAGE 6
LTC2970/LTC2970-1 ELECTRICAL CHARACTERISTICS The ● denotes the speciﬁcations which apply over the full operating temperature range, otherwise speciﬁcations are at TA = 25°C. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS tSETUP_TRACK Tracking IDAC Disconnect Delay LTC2970-1 Only: After the tracking algorithm asserts CPIO_CFG high, the LTC2970-1 will wait this amount of time before starting to decrement Chn_a_ delay_track[9:0]. Used while tracking power supplies off.
PAGE 7
LTC2970/LTC2970-1 U W TYPICAL PERFOR A CE CHARACTERISTICS ADC Total Unadjusted Error vs Temperature ADC INL BASED ON AVERAGE OF 15 PARTS 0.025 ASSEMBLED ON 1/8" THICK PCB 1V 0 ERROR (LSBs) ERROR (%) –0.025 1.8V –0.050 2.5V –0.075 3.3V –0.100 1.00 2.0 0.75 1.5 0.50 1.0 0.5 0 ADC VIN = 5V –0.125 ADC DNL 2.5 ERROR (LSBs) 0.050 –0.
PAGE 8
LTC2970/LTC2970-1 U W TYPICAL PERFOR A CE CHARACTERISTICS IDAC Output Current vs Temperature 257.4 1.620 IDAC CODE = 'hff RIOUT = 13kΩ 257.2 Voltage Buffered IDAC Load Regulation Sourcing 3.500 IDAC CODE = 'h00 25oC 1.615 257.0 256.8 256.6 3.498 OUTPUT VOLTAGE (V) OFFSET VOLTAGE (mV) OUTPUT CURRENT (μA) VOUTn Offset Voltage vs Temperature 1.610 1.605 1.600 1.595 256.2 –50 1.590 –50 75 0 25 50 TEMPERATURE (°C) 100 90oC –25 75 0 25 50 TEMPERATURE (oC) 100 VIOUTn = 3.
PAGE 9
LTC2970/LTC2970-1 U W TYPICAL PERFOR A CE CHARACTERISTICS 400 –100 300 –200 200 –25 NO LOAD ON VDD SHORT-CIRCUIT CURRENT (mA) 0 100 –300 –45°C –400 –500 0 25°C 90°C –700 –45°C –100 –200 –600 –800 VDD Regulator Short-Circuit Current vs Temperature VDD Regulator Line Regulation ΔVDD (ppm) ΔVDD (ppm) VDD Regulator Load Regulation 25°C –300 90°C V12VIN = 12V VDD = 0V –30 –35 –400 V12VIN = 12V 0 –1 –2 –3 CURRENT (mA) –4 –5 –500 8 9 10 29701 G19 10 12 V12VIN (V) 13 14 15
PAGE 10
LTC2970/LTC2970-1 U U U PI FU CTIO S VOUT1 (Pin 12): CH1 Voltage Output. Buffered version of IDAC1 output voltage. IOUT1 (Pin 13): IDAC1 Current Output. Connect a resistor between this pin and the point-of-load ground for channel 1. The IDAC sources between 0 and 255μA. IOUT0 (Pin 14): IDAC0 Current Output. Connect a resistor between this pin and the point-of-load ground for channel 0. The IDAC sources between 0 and 255μA. GPIO_1 (Pin 15): General Purpose Input or Open Drain Digital Output.
PAGE 11
LTC2970/LTC2970-1 W BLOCK DIAGRA 5V REGULATOR VIN VOUT 12VIN 10 2R 0μA TO 255μA IDAC0 8 BITS R 14 IOUT0 VDD VDD 9 + 12VP CMP0 12VM VDDP GND 25 – + VDDM VBUF0 VDD 11 VOUT0 – TEMP SENSOR TSNSP UVLO POR TSNSM VIN0_AP 1 CH0_AP VIN0_AM 2 CH0_AM VIN0_BP 3 CH0_BP VIN0_BM 4 CH0_BM VIN1_AP 5 CH1_AP VIN1_AM 6 CH1_AM 0μA TO 255μA VIN1_BP VIN1_BM 7 8 + – IDAC1 8 BITS 13 IOUT1 14-BIT DELTA-SIGMA A/D + CMP1 ADC CLOCKS CH1_BP + 6.
PAGE 12
LTC2970/LTC2970-1 U U TABLE OF CO TE TS (For Operations Sections) 1. LTC2970 Operation Overview .............................................................................................................................13 2. I2C Serial Digital Interface .................................................................................................................................14 3. Register Command Set..................................................................................................
PAGE 13
LTC2970/LTC2970-1 U OPERATIO 1. LTC2970 Operation Overview The LTC2970 is designed to control and monitor two power supplies. The LTC2970’s superior accuracy allows it to precisely servo each supply’s output voltage over a wide range of operating conditions; increasing accuracy, reducing power requirements and component costs. Margining may be performed with equal ease and precision.
PAGE 14
LTC2970/LTC2970-1 U OPERATIO • Continuously servo one or both supplies to a programmed voltage. • Perform a one-time servo of one or both supplies to a programmed voltage and hold the servo codes in the controlling IDAC. • Perform a one time servo of one or both supplies to a programmed voltage and hold the code(s) in the controlling IDAC(s) until over/under voltage monitoring detects a fault, at which point a control bit may be used to allow the LTC2970 to servo back to the initial voltage target.
PAGE 15
LTC2970/LTC2970-1 U OPERATIO Table 3. Special LTC2970 Addresses Table 2. LTC2970 Address Table ADDRESS[7:0] (R/W = 0) ADDRESS[7:1] ASEL1 ASEL0 8’hB8 7’h5C L L 8’hBA 7’h5D L F 8’hBC 7’h5E L H 8’hBE 7’h5F F L 8’hD6 7’h6B F F 8’hD8 7’h6C F H 8’hDA 7’h6D H L 8’hDC 7’h6E H F 8’hDE 7’h6F H H ADDRESS[7:0] ADDRESS[7:1] FUNCTION (R/W = 0) ARA 8’h18 7’h0C This is the standard Alert Response Address for all SMBus devices.
PAGE 16
LTC2970/LTC2970-1 U OPERATIO 3. Register Command Set (Cont.
PAGE 17
LTC2970/LTC2970-1 U OPERATIO 4. Detailed I2C Command Register Descriptions (Cont.) FAULT_INDEX: Latched Fault Index Register – Read BIT(s) SYMBOL OPERATION b[0] Fault_la_index 0 = All faults indicated by FAULT_LA are clear. IO: Input/Output Data and General Purpose Control Register – Read/Write unless speciﬁed otherwise. BIT(s) SYMBOL OPERATION b[1:0] Io_cfg_0[1:0] Io_cfg_0[1:0] is used to conﬁgure the function of the GPIO_0 pin and IO(Io_gpio_0). 00: Io_gpio_0 = GPIO_0 = Power_good.
PAGE 18
LTC2970/LTC2970-1 U OPERATIO 4. Detailed I2C Command Register Descriptions (Cont.) ADC_MON: ADC Monitoring Mux Control Register – Read/Write VDD_ADC, V12_ADC, CH0_A_ADC, CH0_B_ADC, CH1_A_ADC, CH1_B_ADC, and TEMP_ADC: ADC Conversion Result Registers – Read Only Unless Speciﬁed Otherwise BIT(s) SYMBOL OPERATION b[14:0] Vdd_adc[14:0] Measured data from ADC conversion. 0 = ADC will not convert associated channel. (Default) V12_adc[14:0] 1 = ADC will continuously convert associated channel.
PAGE 19
LTC2970/LTC2970-1 U OPERATIO 4. Detailed I2C Command Register Descriptions (Cont.) b[10] Ch0_a_idac_pol 0 = Use this setting when increasing VOUTn causes (VINn_AP-VINn_AM) to decrease. Inverting conﬁguration common to DC/DC converters with external feedback networks.
PAGE 20
LTC2970/LTC2970-1 U OPERATIO 5. Soft Connecting the LTC2970 to the Power Supply Feedback Node The soft connect feature allows the LTC2970 to connect to the power supply’s feedback node with minimal disturbance to the supply’s output voltage. This is accomplished by comparing the buffered voltage of IOUTn to the voltage at VOUTn and incrementing or decrementing Chn_a_idac[7:0] until the comparator output (COMPn) changes.
PAGE 21
LTC2970/LTC2970-1 U OPERATIO soft connect failed with an IDAC fault (Fault_chn_a_idac = 1). Recall that a new hard connection requires the previous value of Chn_a_idac_en = 0. LTC2970-1 Only: Hard connect requests will be ignored and the user will not be able to change Chn_a_idac_pol, Chn_a_idac_con or Chn_a_idac[7:0] if GPIO_CFG is high and either GPIO_0 or GPIO_1 are high.
PAGE 22
LTC2970/LTC2970-1 U OPERATIO This causes open-drain outputs GPIO_1 and GPIO_0 to automatically pull the power supplies’ run/soft-start pins to ground. CHn_A_IDAC(): Hard connect Chn_a_idac[7:0] with a value that forces the power supplies off when GPIO_CFG = 1. Verify that Chn_a_idac_pol is at the appropriate value.
PAGE 23
LTC2970/LTC2970-1 U OPERATIO LTC2970-1 response: Each tracking enabled channel is soft connected. The GPIO_CFG pin is released allowing it to be pulled high. The LTC2970-1 waits tSETUP_TRACK to allow GPIO_CFG to settle. For each tracking enabled channel, the Chn_a_delay_track counter is decremented at a rate of tDEC_TRACK. As soon as a channel’s tracking counter reaches zero, the LTC2970-1 will begin stepping the value of Chn_a_idac[7:0] by one count until the ﬁnal value of Chn_a_idac_track[7:0] is reached.
PAGE 24
LTC2970/LTC2970-1 U OPERATIO 13. One Time Power Supply Voltage Servo Procedure: The one time voltage servo feature allows the LTC2970 to servo an external power supply to a programmed value and then stop updating the IDAC once the target value has been reached. Follow procedure outlined for “One Time Power Supply Voltage Servo”.
PAGE 25
LTC2970/LTC2970-1 U OPERATIO Table 7.
PAGE 26
LTC2970/LTC2970-1 U OPERATIO Procedure: Update the over-voltage limit register with the value above which the ADC result should generate an over-voltage fault. Instantaneous over-voltage faults are updated after each ADC conversion. They are asserted high when the ADC result is greater than the over-voltage limit. They are cleared if the ADC result is less than or equal to the over-voltage limit. Setting the over-voltage limit to 14’h3fff inhibits instantaneous faults for the associated channel.
PAGE 27
LTC2970/LTC2970-1 U OPERATIO Rules: Rules: See “Generating and Monitoring Instantaneous Faults”. The power on reset conﬁgurations for GPIO_0 and GPIO_1 are output pins with a value equal to the complement of the GPIO_CFG level. 18.
PAGE 28
LTC2970/LTC2970-1 U U W U APPLICATIO S I FOR ATIO ⎛ R20 ⎞ VDC0,NOM = VFB • ⎜ 1+ + I • R20 ⎝ R10 ⎟⎠ FB 4-Step Resistor Selection Procedure for DC/DC Converters with External Feedback Resistors The following 4-step procedure should be used to quickly calculate the resistor values shown for the Typical Application Circuit shown in Figure 1. R20 • R30 (R40 • 236μA − VFB0 − 10mV ) VDC0,MIN ≤ VDC0,NOM − 1.
PAGE 29
LTC2970/LTC2970-1 U W U U APPLICATIO S I FOR ATIO the LTC2970 will automatically ﬁnd the IDAC code that most closely approximates the TRIM pin's open-circuit voltage before enabling VOUT0. Note: The relationship between VTRIM and the converter's output is typically non-inverting, so be sure to set the LTC2970's CH0_a_idac_pol bit to 1 in order to allow the voltage servo feature to function properly.
PAGE 30
LTC2970/LTC2970-1 U U W U APPLICATIO S I FOR ATIO 7-Step Procedure for Calculating Tracking Application Circuit Resistor Values, Counter Delay Values, and Terminal IDAC Codes The following 7-step procedure should be used to calculate the resistor values, tracking counter delays, and terminal IDAC codes for the Tracking Application Circuit shown in Figure 3. 1. Assume a value for R20 and solve for R21.
PAGE 31
LTC2970/LTC2970-1 U W U U APPLICATIO S I FOR ATIO 6. Solve for Channel 1’s tracking counter delay relative to Channel 0, CH1_A_DELAY_TRACK(). CH1_ A _ DELAY _ TRACK() = R31B VDC1,NOM′ − VDC0,NOM′ • R21 (counts) 1μA / count • R41 ( ) (19) From Equation 2: R30 ≤ Note: VDCn,NOMʹ is based on the ﬁnal values of R2n and R1n. If the result for CH1_A_DELAY_TRACK() is less than 0, apply the unsigned result to the CH0_A_DELAY_TRACK() register. 7.
PAGE 32
LTC2970/LTC2970-1 U W U U APPLICATIO S I FOR ATIO VDC0,MAX > VDC0,NOM + R20 • ( VFB0 − 10mV ) R30 10kΩ • 7.68kΩ (0.8V − 10mV ) = 3.660V → VDC0,MAX > 2.631V + From Equation 7, the margining resolution will be less than: R20 • R40 • 276μA R 30 VRES < = 256 10kΩ • 6.65kΩ • 276μA 7.68kΩ = 9.33mV/LSB 256 Margining DC/DC Converter with TRIM Pin Design Example The output voltage of the DC/DC converter in Figure 2 needs to be margined ±10% about its nominal value. Assume that RTRIM = 10.22kΩ and VREF = 1.
PAGE 33
LTC2970/LTC2970-1 U W U U APPLICATIO S I FOR ATIO 4. Solve for R30B and R31B. (R40 • 236μA − VFB0 − 0.8V − 10mV ) = R30B ≤ 1 ⎞ ⎛ 1 + VFB0 • ⎜ ⎝ R10 R20 ⎟⎠ (10.5kΩ • 236μA − 0.8 V − 0.8 V − 10mV) = 2, 870Ω 1 1 ⎞ ⎛ + 0.8 V • ⎜ ⎝ 4, 750Ω 5, 970Ω ⎟⎠ R31B ≤ (R41• 236μA − VFB1 − 0.8V − 10mV ) = 1 ⎞ ⎛ 1 VFB1 • ⎜ + ⎝ R11 R21⎟⎠ (10.5kΩ • 236μA − 0.8 V − 0.8 V − 10mV) = 2, 863Ω 1 1 ⎞ ⎛ + 0.
PAGE 34
LTC2970/LTC2970-1 U U W U APPLICATIO S I FOR ATIO drop across resistor RSENSE. Since the VDD pin voltage is monitored by the LTC2970, its tolerance can be accounted for when calculating the point of load voltage. Transistor Q1 allows the IOUT0 pin to force current into the converter’s feedback node without forward biasing the LTC2970’s IOUT0 body diode. Note that IOUT0’s output current defaults to 128μA after the LTC2970 comes out of power-on reset. 2.7 2.4 VDC1 2.1 VOLTS 1.8 VDC0 1.5 1.2 0.9 0.
PAGE 35
LTC2970/LTC2970-1 U PACKAGE DESCRIPTIO UFD Package 24-Lead Plastic QFN (4mm × 5mm) (Reference LTC DWG # 05-08-1696) 2.65 ± 0.10 (2 SIDES) R = 0.115 TYP 23 24 0.75 ± 0.05 4.00 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.30 TYP 0.70 ±0.05 0.40 ± 0.05 PIN 1 TOP MARK (NOTE 6) 4.50 ± 0.05 1 3.10 ± 0.05 2 2.65 ± 0.05 (2 SIDES) 5.00 ± 0.10 (2 SIDES) 0.25 ±0.05 0.50 BSC 3.65 ± 0.05 (2 SIDES) 4.10 ± 0.05 5.50 ± 0.05 3.65 ± 0.10 (2 SIDES) (UFD24) QFN 0505 0.200 REF PACKAGE OUTLINE 0.00 – 0.05 0.25 ± 0.
PAGE 36
LTC2970/LTC2970-1 U TYPICAL APPLICATIO 8V TO 15V 10 R50 VIN IN 0.1μF 12VIN VDD OUT 9 10k 4 I+ 3 I– DC/DC CONVERTER 0 11 1 R30 GPIO_CFG VIN0_BM 0.1μF 20 VIN0_BP VOUT0 VIN0_AP R20 RUN/SS FB LOAD R10 14 IOUT0 R40 PGND SGND 2 VIN0_AM ALERT SCL 16 SDA GPIO_0 17 18 19 I2C BUS SMBUS COMPATIBLE ( ) LTC2970 R51 VIN IN OUT 8 I+ 7 I– 12 DC/DC CONVERTER 1 5 R31 VIN1_BM VIN1_BP VOUT1 VIN1_AP R21 RUN/SS FB LOAD R11 PGND SGND 13 IOUT1 R41 6 VIN1_AM REF 23 0.