Datasheet

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LTC4425

4425fa

For more information www.linear.com/LTC4425

Typical applicaTion

FeaTures DescripTion

Linear SuperCap Charger

with Current-Limited Ideal

Diode and V/I Monitor

The LT C

4425 is a constant-current/constant-voltage linear

charger designed to charge a 2-cell supercap stack from

either a Li-Ion/Polymer battery, a USB port, or a 2.7V to

5.5V current-limited supply. The part operates as an ideal

diode with an extremely low 50mΩ on-resistance making

it suitable for high peak-power/low average power ap

plications. The LTC4425 charges the output capacitors to

an externally programmed output voltage in LDO mode at

a constant charge current, or to V

in normal mode with

a smart charge current proﬁle to limit the inrush current

until the V

to V

OUT

differential is less than 250mV. In ad-

dition the LTC4425 can be set to clamp the output voltage

to 4.9V or 5.4V.

Charge current (V

OUT

current limit) is programmed by

connecting a resistor between PROG and GND. The volt-

age on the PROG pin represents the current ﬂowing from

to V

OUT

for current monitoring. An internal active

balancing circuit maintains equal voltages across each

supercapacitor and clamps the peak voltage across each

cell to a pin-selectable maximum value. The LTC4425

operates at a very low 20µA quiescent current (shutdown

current <3µA) and is available in a low proﬁle 12-pin

3mm × 3mm DFN or a 12-lead MSOP package.

Charging 2-Cell Series Supercapacitor from Li-Ion Source

applicaTions

50mΩ Ideal Diode from V

to V

OUT

Smart Charge Current Proﬁle Limits Inrush Current

Internal Cell Balancer (No External Resistors)

Programmable Output Voltage (LDO Mode)

Programmable V

to V

OUT

Current Limit

Continuous Monitoring of V

to V

OUT

Current via

PROG Pin

Low Quiescent Current: 20μA

Power Fail, PGOOD Indicator

2.45V/2.7V Cell Protection Shunts

(4.9V/5.4V SuperCap Max Top-Off Voltage)

3A Peak Current Limit, Thermal Limiting

Tiny Application Circuit, 3mm × 3mm × 0.75mm DFN

and 12-Lead MSOP Packages

High Peak Power Battery/USB Powered Equipment

Industrial PDAs

Portable Instruments/Monitoring Equipment

Power Meters, SuperCap Backup Circuits

PC Card/USB Modems

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

LTC4425

GND

–

Li-Ion

OUT

≅

MONITOR

1.5M

1.2M

2.2µF

PFI

PFI_RET

SEL

FROM

µC

2.45V/2.7V

PROG

PFO

470k

TO HIGH PEAK

POWER LOAD

MID

4425 TA01

– V

OUT

(V)

CHARGE CURRENT (A)

0.6

0.5

4425 TA02

0.1

0.2

0.3

0.4

0 0.2 0.4 0.6 0.8

1/10 CHARGE

CURRENT

CURRENT LIMITED

BY PMOS RDSON

IDEAL DIODE

FORWARD VOLTAGE = 15mV

FULL CHARGE CURRENT

= V

PROG

= 2k

Charge Current vs V

to V

OUT

Differential

Downloaded from Arrow.com.

Summary of content (22 pages)

PAGE 1
LTC4425 Linear SuperCap Charger with Current-Limited Ideal Diode and V/I Monitor Description Features n n n n n n n n n n n 50mΩ Ideal Diode from VIN to VOUT Smart Charge Current Profile Limits Inrush Current Internal Cell Balancer (No External Resistors) Programmable Output Voltage (LDO Mode) Programmable VIN to VOUT Current Limit Continuous Monitoring of VIN to VOUT Current via PROG Pin Low Quiescent Current: 20μA VIN Power Fail, PGOOD Indicator 2.45V/2.7V Cell Protection Shunts (4.9V/5.
PAGE 2
LTC4425 Absolute Maximum Ratings (Notes 1, 2) VIN , VOUT, VMID , FB, PFI_RET, PFO Voltage..– 0.3V to 6V EN, SEL, PFI Voltage.....–0.3V to MAX(VIN, VOUT ) + 0.3V Operating Junction Temperature.............– 40°C to 125°C Storage Temperature Range...................– 65°C to 150°C Lead Temperature, MSOP Only (Soldering, 10 sec).................................................
PAGE 3
LTC4425 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C, VIN = 3.8V. (Note 4) SYMBOL PARAMETER VIN Operating Supply Range IQ(IN) Quiescent Current from VIN IQ(OUT) ISD CONDITIONS MIN l TYP 2.7 MAX 5.
PAGE 4
LTC4425 Electrical Characteristics The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C, VIN = 3.8V. (Note 4) SYMBOL PARAMETER CONDITIONS MIN TYP MAX 1.8 1.84 UNITS VMID Output Voltage VOUT = 3.6V 1.76 VMID Maximum Current Sourcing Capability VMID < VOUT/2 , VMID < VCLAMP 0.7 mA VMID Maximum Current Sinking Capability VMID > VOUT/2 , VMID < VCLAMP 1.
PAGE 5
LTC4425 Typical Performance Characteristics LDO Regulation Voltage vs Charge Current LDO Regulation Voltage vs Temperature 3.295 80 VIN = 3.8V 3.285 VOUT SET FOR 3.3V 70 ON-RESISTANCE (mΩ) 3.284 3.285 3.283 3.280 VOUT (V) 3.282 3.275 3.281 3.270 3.280 3.265 3.279 VIN = 3.8V 3.260 RPROG = 1k VOUT SET FOR 3.3V 3.255 200 400 600 800 0 ICHG (mA) 1000 3.
PAGE 6
LTC4425 Typical Performance Characteristics Open Drain Outputs (PFI_RET and PFO) FET On-Resistance vs Temperature 16 0.7 14 0.6 12 RESISTANCE (Ω) VOLTAGE (V) 0.8 18 VIN = 3.8V 0.5 0.4 0.3 6 4 2 –5 15 35 55 TEMPERATURE (°C) 75 –25 –5 15 35 55 TEMPERATURE (°C) 4425 G10 3500 2.85 2.80 75 2.
PAGE 7
LTC4425 Pin Functions VOUT (Pin 1, 2): Output Pin of the Charger. Typically connects to the top of the 2-cell supercap stack. PROG (Pin 3): Charge Current Program and Charge Current Monitor Pin. A resistor connected from PROG to ground programs the charge current. In LDO mode, this pin always servos to 1V. However, if the charge current profile is turned on, this pin servos to a voltage between 1V and 0.1V depending on the input-to-output differential.
PAGE 8
LTC4425 Block Diagram VIN 1.2V BANDGAP 1.11V REFERENCE 0.1V VOUT VIN – 15mV + – MPSNS ×1 MPSW ×1000 VOUT IDEAL DIODE CONTROLLER PSHUNT CONSTANT-VOLTAGE/ CONSTANT-CURRENT/ CONSTANT-TEMPERATURE CHARGER CIRCUITRY 10X VOLTAGE CLAMP CIRCUITRY NSHUNT 1X 250mV 750mV R VIN – VOUT COMPARATOR RPF1 VIN VOUT + 250mV PFI 1.2V RPF2 PFI_RET + – OSCILLATOR CBIG LBA + – 2.7V 2.45V 1.
PAGE 9
LTC4425 Operation LDO Mode In LDO mode, the output voltage VOUT is programmed by an external resistor divider network consisting of RFB1 and RFB2 via the FB pin and the charge current is programmed by an external resistor RPROG via the PROG pin. Please refer to the Block Diagram shown in Figure 1. The charger control circuitry consists of a constantcurrent amplifier and a constant-voltage amplifier.
PAGE 10
LTC4425 Operation Thermal Regulation In either mode, if the die temperature starts to approach 105°C due to internal power dissipation, a thermal regulator limits the die temperature to approximately 105°C by reducing the charge current. Even in thermal regulation, the PROG pin continues to give an indication of the charge current.
PAGE 11
LTC4425 Operation Output Status Monitor Shutdown Mode The LTC4425 has an internal comparator to always monitor the output voltage VOUT . At any time, if VOUT falls below 7.5% of its final programmed value in LDO mode or more than 250mV below the input voltage VIN in charge current profile mode, the comparator reports the power-fail condition by pulling the same open-drain output PFO low.
PAGE 12
LTC4425 Applications Information Programming the Output Voltage Programming the Charge Current In LDO mode, the LTC4425 output voltage can be programmed for any voltage between 2.7V and VIN by using a resistor divider from VOUT pin to GND via the FB pin such that: The LTC4425 charge current is programmed using a single resistor from the PROG pin to ground. The charge current out of the VOUT pin is 1000 times the current out of the PROG pin.
PAGE 13
LTC4425 Applications Information Board Layout Considerations To be able to deliver maximum charge current under all conditions, it is critical that the exposed metal pad on the backside of the LTC4425’s two packages have a good thermal contact to the PC board ground. Correctly soldered to a 2500mm2 double-sided 1 oz. copper board, the DFN package has a thermal resistance of approximately 43°C/W.
PAGE 14
LTC4425 Applications Information Charging a Single Supercapacitor Table 1. Supercapacitor Manufacturers The LTC4425 can also be used to charge a single supercapacitor by connecting two series-connected matched ceramic capacitors (minimum 100µF), or two matched series resistors (~470k), in parallel with the supercapacitor as shown in Figure 5. Refer to Table 1 for supercapacitor manufacturers. LTC4425 VOUT CAP-XX www.cap-xx.com NESS CAP www.nesscap.com Maxwell www.maxwell.com Bussmann www.
PAGE 15
LTC4425 Typical Applications USB to High Peak Power 3.3V Charging USB 5V, 500mA 2.2µF VOUT VIN 3.3V 1F 1.5M 2.1M VMID PFI 1.2M 1F LTC4425 PFI_RET SEL µC TO LOAD FB PFO PROG EN VIO 1.2M 470k 2k 4425 TA03 3 × AA Alkaline to High Peak Power 3.3V Charging 4.5V TO 3.6V 3× AA 2.2µF VOUT VIN 1F 1.5M PFI 1.2M 1F LTC4425 SEL FB PFO EN TO LOAD 2.1M VMID PFI_RET µC 3.3V, 2A VIO 470k 1.
PAGE 16
LTC4425 Typical Applications High Current USB Charging with Power Path Control L1 3.3µH USB INSTANT-ON 5V VIN SW VBUS R1 100k VOUT D0 LDO3V3 D1 µC D2 C1 10µF 0805 C3 10µF 0805 GATE LTC4088 M1 GND C/X R5 8.2Ω R2 100k C2 0.1µF 0603 + R3 2.94k VMID CSC 0.55F HS203F R8 1.2M VIN FB PFI_RET PROG LOAD PFI BAT CLPROG VOUT LTC4425 R7 1.
PAGE 17
LTC4425 Typical Applications 12V to 5V/3.3V High Peak Power Supply 12V D1 VIN VOUT (5V) BOOST 5V 0.1µF 10µH LT3505 61.1k R7 1.5M 68pF VMID GND VC 75k D2 R8 1.2M 10µF 69.8k 1µF CSP2 1F PFI FB PFO 70pF PROG SEL µC EN D1: 1N4148 D2: MBRM140 CSP1, CSP2: CAP-XX HS203F 2.1M FB PFI_RET 11.3k HIGH PEAKPOWER LOAD CSP1 1F LTC4425 SHDN RT 3.3V VOUT VIN SW R6 2k GND 1.2M 4425 TA06 12V Input to 5V Outputs with Input Voltage Monitoring 12V BOOST VIN 2.2µF ON OFF 0.
PAGE 18
LTC4425 Typical Applications Redundant High Peak Power Battery Supplies USB VIN 2.2µF 1.5M VOUT FB TO LOAD 1F VMID PFI LTC4425 1.2M 1F PFI_RET SEL µC EN USB POWER OK 3×AA 2.2µF 1.5M PROG PFO 2k VIN VOUT FB PFI VMID VIO LTC4425 1.2M PFI_RET SEL EN 470k BAT POWER OK PFO PROG 500Ω 4425 TA08 4425fa 18 Downloaded from Arrow.com. For more information www.linear.
PAGE 19
LTC4425 Package Description Please refer to http://www.linear.com/product/LTC4425#packaging for the most recent package drawings. DD Package 12-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1725 Rev A) 0.70 ±0.05 3.50 ±0.05 2.10 ±0.05 2.38 ±0.05 1.65 ±0.05 PACKAGE OUTLINE 0.25 ±0.05 0.45 BSC 2.25 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 ±0.10 (4 SIDES) R = 0.115 TYP 7 0.40 ±0.10 12 2.38 ±0.10 1.65 ±0.10 PIN 1 NOTCH R = 0.
PAGE 20
LTC4425 Package Description Please refer to http://www.linear.com/product/LTC4425#packaging for the most recent package drawings. MSE Package 12-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1666 Rev G) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ±0.102 (.112 ±.004) 5.10 (.201) MIN 2.845 ±0.102 (.112 ±.004) 0.889 ±0.127 (.035 ±.005) 6 1 1.651 ±0.102 (.065 ±.004) 1.651 ±0.102 3.20 – 3.45 (.065 ±.004) (.126 – .136) 12 0.65 0.42 ±0.038 (.0256) (.0165 ±.
PAGE 21
LTC4425 Revision History REV DATE DESCRIPTION A 02/16 Enhanced Charging a Single Supercapacitor section PAGE NUMBER 14 4425fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representaFor more information www.linear.com/LTC4425 tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. Downloaded from Arrow.com.
PAGE 22
LTC4425 Typical Application Embedded Automotive Backup Controller 6V to 36V VIN 2.2µF CAR BATTERY ON OFF BOOST RUN VC LT3684 11, 12 VOUT (5V) BD 9 D1 RT 28.7k 7 8 200k GND 10µF µC CSP1 1F 10 CSP2 1F PFI LTC4425 590k FB PG VMID R8 1.2M BIAS 330pF 5V, 2A FB SW 20k 1, 2 5 R7 1.5M L1 0.1µF 2.2µH VOUT VIN 4 6 PROG PFI_RET 3 R6 500Ω PFO SEL EN GND 13 4425 TA09 22µF SVIN PVIN, 1, 2, 3 SW1 L2 2.2µH 3.3V 20pF EN1 FB1 EN2 EN3 L3 2.