BQ2057CSN BENCHMARQ, BQ2057CSN Datasheet - Page 16

• Manufacturer Part Number: BQ2057CSN
• Description: PROG BATTERY CHARGER, 2057, SOIC8
• Manufacturer: BENCHMARQ

Specifications of BQ2057CSN

• Battery Type: Li-Ion / Li-Polymer
• Input Voltage: 15V
• Battery Charge Voltage: 4.2V
• Charge Current Max: 2A
• Battery Ic Case Style: SOIC
• No. Of Pins: 8
• No. Of Series Cells: 1
• Operating Temperature: RoHS Compliant

16
SLUS025F − MAY 2001 − REVISED JULY 2002
selecting an external pass-transistor (continued)
P-channel MOSFET:
Selection steps for a P-channel MOSFET: Example: V
(bq2057C). V
1. Determine the maximum power dissipation, P
2. Determine the package size needed in order to keep the junction temperature below the manufacturer’s
3. Select a drain-source voltage, V
4. Select a device that has at least 50% higher drain current (I
5. Verify that the available drive is large enough to supply the desired charge current.
Now choose a P-channel MOSFET transistor that is rated for VDS ≤ −15 V, θ
V
(GSth)
The worst case power dissipation happens when the cell voltage, V
the beginning of current regulation phase) and V
Where V
voltage drop across the current sense resistor.
recommended value, T
Now choose a device package with a theta at least 10% below this value to account for additional thetas
other than the device. A TSSOP-8 package, for instance, has typically a theta of 70°C/W.
adequate in this example.
Where V
(if one is used), and V
output low voltage specification for the bq2057.
Select a MOSFET with gate threshold voltage, V
P
P
P
θ
θ
θ
≥ −3.5 V and in a TSSOP package.
V
V
V
JC
JC
JC
D
D
D
(GS)
(GS)
(GS)
= (V
= (5.5 – 0.4 – 0.1 −3) × 0.5 A
= 1 W
(GS)
+
+
+ 110°C W
D
I
is the input voltage to the charger and I
is the forward voltage drop across the reverse-blocking diode (if one is used), and V
= (V
= (0.4 + 0.1 + 1.5) – 5.5
= −3.5
( 150–40 )
I
T
– V
is the gate-to-source voltage, V
max(J)
1
D
D
+V
− V
P
(CS)
–T
CS
(CS)
D
JMAX
A(max)
+ V
is the voltage drop across the current sense resistor, and V
– V
. Calculate the total theta, θ(°C/W), needed.
OL(CC)
APPLICATION INFORMATION
(BAT)
(DS)
) × I
) − V
, rating greater than the maximum input voltage. A 12 V device will be
(REG)
I
www.ti.com
D
D
is the forward voltage drop across the reverse-blocking diode
, in the transistor.
I
(GSth)
is at its maximum.
(REG)
I
= 5.5 V, I
, rating less than the calculated V
is the desired charge current. (See Figure 4.)
D
) rating than the desired charge current I
(REG)
(BAT)
= 500 mA, 4.2-V single-cell Li−Ion
, is at its lowest (typically 3 V at
JC
≤ 110°C/W, I
OL(CC)
(GS)
is the CC pin
.
D
CS
≥ 1 A,
(REG)
is the
(10)
(12)
(11)
.