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LTC1645

1645fa

Dual-Channel Hot Swap

Controller/Power Sequencer

The LTC

1645 is a 2-channel Hot Swap

controller that

allows a board to be safely inserted and removed from a

live backplane. Using external N-channel pass transistors,

the supply voltages can be ramped at a programmable

rate. Two high side switch drivers control the N-channel

gates for supply voltages ranging from 1.2V to 12V. The

two channels can be set to ramp up and down separately,

or they can be programmed to rise and fall simultaneously,

ensuring power supply tracking at the two outputs.

Programmable electronic circuit breakers protect against

shorts at either output. The RESET output can be used to

generate a system reset when a supply voltage falls below

a user-programmed voltage. An additional spare com-

parator is available for monitoring a second supply

voltage.

The LTC1645 is available in the 8- and 14-pin SO packages.

■

Hot Board Insertion

■

Power Supply Sequencing

■

Electronic Circuit Breaker

■

Allows Safe Board Insertion and Removal from a

Live Backplane

■

Programmable Power Supply Sequencing

■

Programmable Electronic Circuit Breaker

■

User-Programmable Supply Voltage Power-Up and

Power-Down Rate

■

High Side Drivers for External N-Channel FETs

■

Controls Supply Voltages from 1.2V to 12V

■

Ensures Proper Power-Up Behavior

■

Undervoltage Lockout

■

Glitch Filter Protects Against Spurious RESET Signals

■

8- and 14-Pin SO Packages

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

Hot Swap is a trademark of Linear Technology Corporation.

5V and 3.3V Hot Swap

5V and 3.3V Hot Swap Waveforms

5V/DIV

GATE

10V/DIV

OUT2

5V/DIV

OUT1

5V/DIV

0.005Ω*

IRF7413

0.005Ω*

10Ω

10k

LOAD2

LOAD1

OUT1

OUT2

3.3V

1645 TA01

0.01µF

25V

0.01µF

25V

IN2

IN1

GND

PLUG-IN CARDBACKPLANE

SENSE1 V

CC2

GATE1 SENSE2

GATE2

LTC1645

(8-LEAD)

CONNECTOR 1

CONNECTOR 2

CC1

*LRF1206-01-R005-J (IRC)

FEATURES

DESCRIPTIO

APPLICATIO S

TYPICAL APPLICATIO

Summary of content (24 pages)

PAGE 1
LTC1645 Dual-Channel Hot Swap Controller/Power Sequencer U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Allows Safe Board Insertion and Removal from a Live Backplane Programmable Power Supply Sequencing Programmable Electronic Circuit Breaker User-Programmable Supply Voltage Power-Up and Power-Down Rate High Side Drivers for External N-Channel FETs Controls Supply Voltages from 1.
PAGE 2
LTC1645 W W W AXI U U ABSOLUTE RATI GS (Note 1) Supply Voltage (VCC1, VCC2) ................................. 13.2V Input Voltage FB, ON, COMP + ..................... – 0.3V to (VCC1 + 0.3V) TIMER ................................................. – 0.3V to 2.5V SENSE1 ..................... (VCC1 – 0.7V) to (VCC1 + 0.3V) SENSE2 ...................... (VCC1 – 0.7V) to (VCC2 + 0.3V) Output Voltage RESET, COMPOUT, FAULT .....................– 0.3V to 16V GATE1, GATE2 .................
PAGE 3
LTC1645 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. 2.375V ≤ VCC1 ≤ 12V, 1.2V ≤ VCC2 ≤ 12V unless otherwise noted (Note 2). SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 1.212 1.230 1.255 1 9 mV VTM TIMER Pin Voltage Threshold ∆VTM TIMER Pin Threshold Line Regulation VCC1 = 2.375V to 12V ● ITM TIMER Pin Current Timer On, VTIMER = 0.6V, VCC1 = 5V Timer Off, VTIMER = 1.
PAGE 4
LTC1645 U W TYPICAL PERFOR A CE CHARACTERISTICS GATE Voltage vs Supply Voltage Glitch Filter Time vs Feedback Transient GATE Voltage vs Temperature 16.0 25 100 VCC1 = 5V 15.8 VCC2 = 3.3V TA = 25°C GLITCH FILTER TIME (µs) 15.6 20 GATEn (V) GATEn (V) 15.4 15 10 15.2 15.0 14.8 14.6 70 60 50 40 30 14.4 20 14.2 10 0 14.0 –40 – 20 4 3 5 6 7 8 9 HIGHEST VCC (V) 10 11 12 0 40 20 0 60 TEMPERATURE (°C) 800 VCC1 = 5V 400 OUTPUT VOLTAGE (mV) 250 200 150 SINK CURRENT = 1.
PAGE 5
LTC1645 U U U PI FU CTIO S (14-Lead Package/8-Lead Package) VCC2 (Pin 1/Pin 1): Positive Supply Input. VCC2 can range from 1.2V to 12V for normal operation. ICC2 is typically 0.2mA. An undervoltage lockout circuit disables the LTC1645 whenever the voltage at VCC2 is less than 1.12V. SENSE2 (Pin 2/Pin 2): VCC2 Circuit Breaker Set Pin. With a sense resistor placed in the supply path between VCC2 and SENSE2, the circuit breaker trips when the voltage across the resistor exceeds 50mV for more than 1.5µs.
PAGE 6
LTC1645 U U U PI FU CTIO S (14-Lead Package/8-Lead Package) the circuit breaker trips or the undervoltage lockout circuit trips, the GATE1 pin is immediately pulled to ground with a 12mA (typ) current source. Whenever the timer is inactive, an internal N-channel FET shorts the TIMER pin to ground. Activating the timer connects a 2µA current source from VCC1 to the TIMER pin and the voltage starts to ramp up with a slope dv/dt = 2µA/ CTIMER. When the voltage reaches the trip point (1.
PAGE 7
LTC1645 U W U U APPLICATIO S I FOR ATIO Hot Circuit Insertion Power Supply Tracking and Sequencing When a circuit board is inserted into a live backplane, the supply bypass capacitors on the board can draw huge transient currents from the backplane power bus as they charge. These transient currents can cause permanent damage to the connector pins and produce glitches on the system supply, resetting other boards in the system.
PAGE 8
LTC1645 U W U U APPLICATIO S I FOR ATIO Power Supply Ramping The power supplies on a board are controlled by placing external N-channel pass transistors in the power paths as shown in Figure 2. Consult Table 1 for a selection of N-channel FETs suitable for use with the LTC1645. RSENSE1 and RSENSE2 provide current fault detection and R1 and R2 prevent high frequency oscillation.
PAGE 9
LTC1645 U W U U APPLICATIO S I FOR ATIO No bulk capacitance is present to slow the rate of rise and heavily damp the parasitic resonance. Instead, the fast edge shock excites a resonant circuit formed by a combination of wiring harness, backplane and circuit board parasitic inductances and FET capacitance. In theory, the peak voltage should rise to 2X the input supply, but in practice the peak can reach 2.5X, owing to the effects of voltage dependent FET capacitance.
PAGE 10
LTC1645 U W U U APPLICATIO S I FOR ATIO R1 0.01Ω IRF7413 VOUT 12V CLOAD 10Ω D1* 2V/DIV + – PCB EDGE CONNECTOR 12V POWER LEADS BACKPLANE CONNECTOR + 0.1µF LTC1645 0V 1645 F06 1µs/DIV ON SEMICONDUCTOR * 1SMA12CAT3 1645 F06a VCC Waveform Clamped by a Transient Suppressor Figure 6. Transient Suppressor Clamp R1 0.01Ω IRF7413 + – PCB EDGE CONNECTOR 12V POWER LEADS BACKPLANE CONNECTOR + 10Ω VOUT CLOAD 10Ω 0.1µF 0.
PAGE 11
LTC1645 U W U U APPLICATIO S I FOR ATIO SUPPLY GLITCH 12V + – R1 0.01Ω If a dead short occurs after a supply connection is made (Figure 8), the sense resistor R1 and the RDS(ON) of the fully enhanced FET provide a low impedance path for IRF7413 2µH 10Ω + 100µF 0.1µF LTC1645 BOARD WITH POSSIBLE SHORT-CIRCUIT FAULT LTC1645 Hot Swap circuits on the backplane are generally used to provide power-up/down sequence at insertion/ removal as well as overload/short-circuit protection.
PAGE 12
LTC1645 U W U U APPLICATIO S I FOR ATIO nearly unlimited current flow. The LTC1645 discharges the GATE pin in a few microseconds, but during this discharge time current on the order of 150 amperes flows from the VCC power supply. This current spike glitches the power supply, causing VCC to dip (Figure 8a and 8b). On recovery from overload, some supplies may overshoot. Other devices attached to this supply may reset or malfunction and the overshoot may also damage some components.
PAGE 13
LTC1645 U W U U APPLICATIO S I FOR ATIO voltage on the external capacitor CTIMER starts to ramp up with a slope dv/dt = 2µA/CTIMER. When the voltage reaches the trip point (1.23V), the timer is reset by pulling the TIMER pin back to ground. The timer period is t = (1.23V • CTIMER)/2µA. For a 200ms delay, use a 0.33µF capacitor. Electronic Circuit Breaker The LTC1645 features an electronic circuit breaker function that protects against short circuits or excessive output currents.
PAGE 14
LTC1645 U W U U APPLICATIO S I FOR ATIO An external hard reset is initiated at time point 6. The ON pin is forced below 0.8V but above 0.4V, and the GATEn pin voltages start to ramp down. VOUTn also starts to ramp down, and RESET goes low when VOUT2 drops below the power-good trip level at time point 7.
PAGE 15
LTC1645 U W U U APPLICATIO S I FOR ATIO VIN2 5V/DIV VIN1 5V/DIV VOUT2 5V/DIV VOUT1 5V/DIV TIMER 2V/DIV RESET 5V/DIV Figure 16. Ramping 3.3V and 2.5V Up and Down Together This circuit guarantees that: (1) VOUT1 never exceeds VOUT2 by more than 1.2V, and (2) VOUT2 is never greater than VOUT1 by more than 0.4V. On power-up, VOUT1 and VOUT2 ramp up together. On power-down, the LTC1645 turns off Q1 and Q2 simultaneously.
PAGE 16
LTC1645 U W U U APPLICATIO S I FOR ATIO 0.005Ω* BOTH CURRENT LIMITS: 10A VIN2 3.3V IRF7413 + CLOAD2 0.005Ω* VIN1 5V IRF7413 + CLOAD1 D1 1N4148 10Ω 13k 1% 10k R1 47.5k 1% 13 0.01µF 25V 12 1 VCC1 SENSE1 GATE1 10 3 2 VCC2 SENSE2 GATE2 COMP+ ON R2 10k 1% LTC1645 (14-LEAD) COMPOUT 4 RESET FAULT TIMER 10k 10k 28k 1% 8 14.7k 1% RHYST 681k FB FAULT VOUT1 5V 5A 10Ω 0.01µF 25V 14 VOUT2 3.3V 5A 10k 1% 9 µP RESET2 6 10k 1% 5 GND 11 µP RESET 7 1645 F17 0.
PAGE 17
LTC1645 U W U U APPLICATIO S I FOR ATIO goes high which turns on Q3. This lowers the voltage on the gate of Q2. This feedback loop is compensated by capacitors C1 and C2 and resistor R1. When power is first applied, the FB pin is low and RESET holds one side of C2 low, slowing the ramp-up of VOUT2. As VOUT2 exceeds 2.75V, RESET releases to allow improved loop transient response. Figure 20 shows the load transient response and voltage ripple of the generated supply.
PAGE 18
LTC1645 U W U U APPLICATIO S I FOR ATIO Switching Regulator Supply Sequencing Switching Regulator Hot Swapping Figure 21 shows the LTC1645 sequencing two power supplies, the lower of which is generated by the LTC1430A switching regulator. Connecting the regulator’s FB pin resistor divider (R1 and R2) to the other side of the pass FET (Q1) allows the LTC1430A to compensate for the voltage drop across RSENSE1 and Q1, assuring an accurate voltage output.
PAGE 19
FAULT ON/OFF 10k 1µF 270pF 15µF 10V + 4700pF 22k 1500µF 6.3V ×3 6 5 8 7 0.1µF 51Ω COMP SHDN G2 PVCC2 GND FB G1 PVCC1 LTC1430ACS8 3 4 1 2 0.1µF + 130k 1% 162k 1% 1500µF 6.3V ×2 VREGOUT 1µF 1µF R2 16.9k 1% *LRF1206-01-R010-J (IRC) 4700pF 1Ω 2.4µH CDRH1272R4 R1 16.5k 1% 4 10 13 12 FAULT ON 7 GND LTC1645 (14-LEAD) 10Ω RESET FB COMPOUT COMP+ 3 1 2 VCC2 SENSE2 GATE2 0.047µF 25V 11 0.33µF TIMER VCC1 SENSE1 GATE1 14 10Ω RSENSE1* Q1 0.
PAGE 20
FAULT 10k + 0.33µF 100k 0.1µF 0.1µF 14 0.1µF 1.82k 1% 4 FAULT 4.99k VCC1 1% 10 ON 0.33µF MBR0530LT1 1500µF 6.3V ×6 VREGIN D2 MBR0530T1 10µF *LRF2010-01-R003-J (IRC) **MBRS340T (ON SEMICONDUCTOR) †ETQP6F1R2HFA (PANASONIC) GND 10Ω + 12 C– VIN SS 3 7 GND COMPOUT COMP+ RESET FB 9 8 5 6 + 18k 0.047µF 25V 100µF 0.1µF 10k 33k 0.015µF 1.87k 1% 2.67k 1% 220pF IRF7801 IRF7801 Figure 23. Switching Regulator Hot Swap 0.
PAGE 21
LTC1645 U W U U APPLICATIO S I FOR ATIO Table 1. N-Channel Selection Guide ON 2V/DIV CURRENT LEVEL PART NUMBER MANUFACTURER DESCRIPTION 1A to 2A NDH8503N Fairchild Dual N-Channel RDS(ON) = 0.033 SuperSOT-8 1A to 2A Si6928DQ Vishay/Siliconix Dual N-Channel RDS(ON) = 0.035 TSSOP-8 2A to 5A Si4920DY Vishay/Siliconix Dual N-Channel RDS(ON) = 0.025 SO-8 2A to 5A IRF7313 International Rectifier Dual N-Channel RDS(ON) = 0.
PAGE 22
LTC1645 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .053 – .069 (1.346 – 1.752) .014 – .019 (0.355 – 0.
PAGE 23
LTC1645 U PACKAGE DESCRIPTIO S Package 14-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) .337 – .344 (8.560 – 8.738) NOTE 3 .045 ±.005 .050 BSC 14 N 12 11 10 9 8 N .245 MIN .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) 1 .030 ±.005 TYP 13 2 3 N/2 N/2 RECOMMENDED SOLDER PAD LAYOUT 1 .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 2 3 4 5 6 .053 – .069 (1.346 – 1.752) .004 – .010 (0.101 – 0.254) 0° – 8° TYP .016 – .
PAGE 24
LTC1645 U TYPICAL APPLICATIO Dual Supply Hot Swap with Tracking Outputs BOTH CURRENT LIMITS: 5A Q1 1/2 Si4920DY 0.01Ω* VIN1 3.3V D1 1N4002 VIN2 2.5V D2 1N4002 10Ω Q2 0.01Ω* 1/2 Si4920DY + CLOAD1 D3 MBR0530T1 VOUT1 3.3V 2.5A VOUT2 2.5V 2.5A + CLOAD2 10k 10Ω 14 4.99k 1% TRIP POINT: 3V 13 12 VCC1 SENSE1 GATE1 10 1 VCC2 SENSE2 GATE2 COMP+ ON 1.82k 1% COMPOUT LTC1645 (14-LEAD) 4 1.18k 1% FB 8 9 1.18k 1% 6 5 FAULT TIMER 11 0.33µF 1.37k 1% GND 10k 0.1µF 25V 3 2 1.