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PDF DS2703 Data sheet ( Hoja de datos )
| Número de pieza | DS2703 | |
| Descripción | SHA-1 Battery Pack Authentication IC | |
| Fabricantes | Dallas Semiconductor | |
| Logotipo |  |
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www.maxim-ic.com
GENERAL DESCRIPTION
The DS2703 provides a robust cryptographic solution
to ensure the authenticity of Li-Ion battery packs for
cell phone, PDA, and portable computing devices.
The DS2703 employs the Secure Hash Algorithm
(SHA-1) specified in the Federal Information
publication 180-1 and 180-2, and ISO/IEC 10118-3.
SHA-1 is designed for authentication¾just what is
required for identifying battery packs manufactured
by authorized sources.
The device’s SHA-1 engine processes a host
transmitted challenge using its stored 64-bit secret
key and unique 64-bit ROM ID to produce a 160-bit
response word for transmission back to the host. The
secret key is securely stored on-chip and never
transmitted between the battery and the host. A
DS2703-based system produces a high degree of
authentication security between a host system and its
removable battery or other peripheral devices.
The Thermistor Multiplexer feature allows a three
contact battery pack configuration to support data
and thermistor functions. When activated through
1-Wire command, the THM pin presents the
thermistor impedance on the data contact and
disconnects internal loading from the node.
TYPICAL OPERATING CIRCUIT
PACK +
BATTERY PACK
DATA 150W
DS2703
DQ VB
PACK -
THM
VSS
0.22 mF
Li-Ion
Protection
DS2703
SHA-1 Battery Pack
Authentication IC
FEATURES
§ Secure Challenge and Response Authentication
Using the SHA-1 Algorithm
§ Directly Powered by the Dallas 1-Wire® Interface
with 16kpbs Standard and 143kpbs Overdrive
Communication Modes
§ Unique 64-Bit Serial Number
§ Thermistor Multiplexer
§ Operates with VPULLUP as Low as 2.7V
§ mMax-8 Package (Lead-Free)
ORDERING INFORMATION
PART
TEMP RANGE PIN-PACKAGE
DS2703U
DS2703U/T&R
-20°C to +70°C
-20°C to +70°C
mMax-8
DS2703U on
Tape-and-Reel
DS2703U+
-20°C to +70°C
DS2703U+T&R -20°C to +70°C
+ Denotes lead-free package.
mMax-8
DS2703U+ on
Tape-and-Reel
APPLICATIONS
2.5G/3G Wireless Handsets
PDAs
Handheld or Notebook Computers and Terminals
Digital Still and Video Cameras
PIN CONFIGURATION
TOP VIEW
THM
VSS
DQ
VB
18
27
36
45
mMAX
DS2703U+
NC
NC
NC
NC
1-Wire is a registered trademark of Dallas Semiconductor.
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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REV: 071805
1 page  
DS2703 SHA-1 Battery Pack Authentication IC
DETAILED DESCRIPTION
The DS2703 is comprised of a SHA-1 Authentication function and thermistor mux control that are accessed via a 1-
Wire interface. The high voltage (HV) detection circuit routes the externally supplied programming voltage to the
EEPROM array and enables the internal regulator to isolate portions of the chip from the programming voltage. The
1-Wire interface controls access by a host system to the 64-bit Net Address (ROM ID) and SHA-1 Authentication.
The DS2703 operates in one of four operating modes: communication, computation, programming and thermistor
access. Most operations are performed in communication mode, with the host system addressing the DS2703
using Net Address commands and then setting up an authentication exchange and retrieving the results. In
communication mode, the DQ load current averages 5mA maximum, and the DS2703 can be “parasite” powered
via the DQ pin through a high impedance pullup resistor during a communication transaction. Power available while
the 1-Wire bus is at a logic high is rectified by the on chip diode and stored in an off chip capacitor connected to the
VB pin. The voltage regulator operates in a low impedance drop-out mode in the communication mode.
In computation mode, when a SHA-1 verification is performed, the DQ load current increases up to 1mA,
necessitating a lower impedance pullup resistor. The computation mode load current occurs after the host supplies
the required challenge data and requests the computation using the proper function commands in communication
mode. In this mode, the pullup supply and low impedance pullup resistor must be capable of keeping the DQ pin
above VPULLUP-MIN. The voltage regulator operates in a low impedance drop-out mode.
The third operating mode is required when programming the non-volatile memory portions of the DS2703. The
programming mode is defined by the application of a high voltage programming pulse to the DQ pin at the
appropriate point during a Compute Secret command, Load/Lock Secret or Clear/Set Overdrive Timing command.
The internal voltage regulator limits the internal voltage (VDD_INT) to isolate low voltage portions of the chip from the
HV programming pulse. Typically, programming mode is used during module or pack manufacture to configure the
DS2703 and program the 64-bit secret.
Finally, thermistor mode allows the voltage on an external thermistor to be measured from the DQ line. The
command sequence causes the DS2703 to internally disconnect its DQ interface and drive the THM pin to VSS
allowing the measurement to be made. The IC remains in this mode until the VB pin capacitor is drained causing
the DS2703 to power cycle back to communication mode.
AUTHENTICATION
Authentication is performed using a FIPS-180 compliant SHA-1 one way hash algorithm on a 512 bit message
block. The message block consists of a 64-bit secret, a 64-bit challenge and 384 bits of constant data. Optionally,
the 64-bit net address replaces 64 of the 384 bits of constant data used in the hash operation. An authentication
attempt is initiated by the host system providing a 64-bit random challenge then sending one of two compute
command sequences. The host and the DS2703 both calculate the result based on the mutually known secret. The
result data, known as the Message Authentication Code (MAC) or Message Digest, is returned by the DS2703 for
comparison to the host’s result. Note that the secret is never transmitted on the bus and thus cannot be captured
by observing bus traffic. SHA-1 based authentication is a cryptographically strong method in wide use for digitally
signing encrypted files and secure transactions such as electronic cash and password exchange protocols.
The FIPS 180 Compliant Input Block, the 512-bit message block is organized as sixteen 32-bit words, W0-W15.
The message block is initialized when a command is received to compute the MAC. Upon initialization, the 64-bit
secret is loaded, and it is important to note that the SHA-1 algorithm has access to this data, but not the serial
interface. The challenge data is received with the command just prior to the compute MAC command. The
challenge data is cleared during computation of the MAC, so the host must write new challenge data prior to
issuing each Compute MAC or Compute Next Secret command. Additionally, the A, B, C, D and E variables used
in the hash computation are initialized per FIPS 180 as shown in Table 1. Variable Initiation.
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5 Page 
DS2703 SHA-1 Battery Pack Authentication IC
HARDWARE CONFIGURATION
The DS2703 uses an open-drain output driver as part of the bidirectional interface circuitry shown in Figure 5. If a
bidirectional pin is not available on the bus master, separate output and input pins can be connected together. For
normal communication the 1-Wire bus must have a pullup resistor at the bus-master end of the bus. For short line
lengths and/or VPULLUP ≥ 3.0V, a value of approximately 4.7kW is recommended. For long line lengths and/or
VPULLUP < 3.0V, a value of approximately 2kW is recommended. The idle state for the 1-Wire bus is high. If, for any
reason, a bus transaction must be suspended, the bus must be left in the idle state to properly resume the
transaction later. Note that if the bus is left low for more than tLOW0, slave devices on the bus begin to interpret the
low period as a reset pulse, effectively terminating the transaction.
When performing SHA-1 computations, the DS2703 requires a stronger pullup than 4.7k. A P-FET in parallel with
the standard pullup can be switched on during computation and then disabled to read the result. When measuring
the thermistor RTHM, both the strong pullup and standard pullup should be disabled to allow a weak pullup to form a
voltage divider with the thermistor. A voltage A/D connected directly to the 1-Wire bus can then read the voltage
drop of the thermistor.
Figure 5. 1-Wire Bus Interface Circuitry
VPULLUP
COMP
COMM
Voltage A/D
Rx
Tx
Bus Master
4.7K 50K
150
DQ
~1µA
RTHM
~100Ω
MOSFET
Rx
Tx
PACK-
DS2703
Activate
THM
TRANSACTION SEQUENCE
The protocol for accessing the DS2703 through the 1-Wire port is as follows:
§ Initialization
§ Net Address Command
§ Function Command(s)
§ Data Transfer (not all commands have data transfer)
All transactions of the 1-Wire bus begin with an initialization sequence consisting of a reset pulse transmitted by the
bus master, followed by a presence pulse simultaneously transmitted by the DS2703 and any other slaves on the
bus. The presence pulse tells the bus master that one or more devices are on the bus and ready to operate. For
more details, see the 1-Wire Signaling section below.
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11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet DS2703.PDF ] | |
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